Patent Publication Number: US-10788037-B2

Title: Scroll compressor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is entitled to the benefit of and incorporates by reference subject matter disclosed in the International Patent Application No. PCT/IB2014/064550 filed on Sep. 16, 2014 and French Patent Application No. 13/59729 filed on Oct. 8, 2013. 
     TECHNICAL FIELD 
     The present invention relates to a scroll compressor, and in particular to a scroll refrigeration compressor. 
     BACKGROUND 
     U.S. Pat. No. 5,775,893 discloses a scroll compressor including:
         a closed container,   a scroll compression unit including:
           a first fixed scroll and a second fixed scroll defining an inner volume, the first fixed scroll comprising a first fixed spiral wrap, the second fixed scroll comprising a second fixed spiral wrap,   an orbiting scroll arrangement disposed in the inner volume, the orbiting scroll arrangement including a first orbiting spiral wrap and a second orbiting spiral wrap, the first fixed spiral wrap and the first orbiting spiral wrap forming a plurality of first compression chambers, the second fixed spiral wrap and the second orbiting spiral wrap forming a plurality of second compression chambers,   
           a refrigerant suction pipe for supplying the inner volume with refrigerant to be compressed,   a refrigerant discharge pipe arranged for discharging the compressed refrigerant outside the scroll compressor,   a drive shaft including a driving portion adapted for driving the orbiting scroll arrangement in an orbital movement, and   a driving motor arranged for driving in rotation the drive shaft about a rotation axis, the driving motor being located nearby the first fixed scroll and including a rotor coupled to the drive shaft and a stator.       

     According to such a scroll compressor, the central compression chambers of the first and second compression chambers are fluidly connected with each other such that the refrigerant compressed in the first and second compression chambers is discharged in a common upper discharge space fluidly connected the refrigerant discharge pipe, the compressed refrigerant being then guided outside of the closed container through the refrigerant discharge pipe. 
     Such a configuration of the scroll compressor prevents a satisfactory cooling of the driving motor with the compressed refrigerant, and thus reduces the efficiency of the scroll compressor. 
     SUMMARY 
     It is an object of the present invention to provide an improved scroll compressor which can overcome the drawbacks encountered in conventional scroll compressors. 
     Another object of the present invention is to provide a scroll compressor which is reliable and has an improved efficiency compared to the conventional scroll compressors. 
     According to the invention such a scroll compressor includes:
         a closed container,   a scroll compression unit including:
           a first fixed scroll and a second fixed scroll defining an inner volume, the first fixed scroll comprising a first fixed base plate and a first fixed spiral wrap, the second fixed scroll comprising a second fixed base plate and a second fixed spiral wrap,   an orbiting scroll arrangement disposed in the inner volume, the orbiting scroll arrangement including a first orbiting spiral wrap and a second orbiting spiral wrap, the first fixed spiral wrap and the first orbiting spiral wrap forming a plurality of first compression chambers, the second fixed spiral wrap and the second orbiting spiral wrap forming a plurality of second compression chambers,   
           a drive shaft including a driving portion adapted for driving the orbiting scroll arrangement in an orbital movement,   a driving motor arranged for driving in rotation the drive shaft about a rotation axis, the driving motor including a rotor coupled to the drive shaft and a stator, the first fixed base plate having a first face directed towards the driving motor and a second face opposite to the first face and directed towards the second fixed scroll,   wherein the first fixed scroll includes at least one first discharge passage arranged to conduct, in use, the refrigerant compressed in the first compression chambers towards the driving motor, and particularly in direction of the driving motor, and   wherein the orbiting scroll arrangement includes at least one communicating hole arranged to fluidly connect a central first compression chamber and a central second compression chamber.       

     The configuration of the at least one first discharge passage allows to force the refrigerant compressed in the first compression chambers to flow along a large part of the driving motor before being discharged outside the scroll compressor, which improve the cooling of the driving motor, and thus the efficiency of the scroll compressor. 
     According to an embodiment of the invention, the at least one first discharge passage emerges in the first face of the first fixed base plate. 
     According to an embodiment of the invention, the driving motor is arranged nearby the first fixed scroll. 
     According to an embodiment of the invention, the stator includes a first winding head directed towards the first fixed scroll and a second winding head opposite to the first winding head, the scroll compressor further including an intermediate casing surrounding the stator and in which the driving motor is at least partially mounted, the intermediate casing and the driving motor at least partially defining a proximal chamber containing the first winding head of the stator. 
     According to an embodiment of the invention, the at least one first discharge passage emerges nearby the driving motor, notably nearby the stator, and for example nearby the first winding head of the stator. 
     According to an embodiment of the invention, the at least one first discharge passage is oriented towards the driving motor, and for example towards the first winding head of the stator. 
     According to an embodiment of the invention, the at least one first discharge passage emerges in the proximal chamber. This arrangement of the at least one first discharge passage allows to force the refrigerant compressed in the first compression chambers to flow along the first winding head of the stator, the air gaps between the stator and the rotor and the possible refrigerant flow passages defined between the intermediate casing and the stator. Such provisions further improve the cooling of the driving motor, and thus the efficiency of the scroll compressor. 
     According to an embodiment of the invention, the at least one first discharge passage is fluidly connected to the central first compression chamber, and is arranged to conduct the refrigerant compressed in the central first compression chamber towards the driving motor. 
     According to an embodiment of the invention, the first fixed scroll and the drive shaft define a first annular chamber fluidly connected to the central first compression chamber, the at least one first discharge passage being fluidly connected to the first annular chamber, and advantageously emerging in the first annular chamber. 
     According to an embodiment of the invention, the intermediate casing and the driving motor define a distal chamber containing the second winding head of the stator, the intermediate casing being provided with at least one refrigerant discharge aperture emerging in the distal chamber. These provisions ensure a more efficient cooling of the second winding head and limit the oil circulating rate, i.e. the amount of oil going out of the scroll compressor. 
     According to an embodiment of the invention, the driving motor is entirely mounted in the intermediate casing. Preferably, the intermediate casing includes a side part surrounding the driving motor and a closing part arranged for closing an end portion of the side part. 
     According to an embodiment of the invention, the intermediate casing and the stator define at least one refrigerant passage arranged to fluidly connect the proximal chamber to the distal chamber. 
     According to an embodiment of the invention, the rotor and the stator define at least one refrigerant passage arranged to fluidly connect the proximal chamber to the distal chamber. 
     According to an embodiment of the invention, the at least one first discharge passage is inclined relative to the rotation axis of the drive shaft. 
     According to an embodiment of the invention, the first fixed scroll includes a plurality of first discharge passages. The first discharge passages may be for example angularly offset from each other in relation to the rotation axis of the drive shaft. 
     According to an embodiment of the invention, the intermediate casing and the closed container define an annular volume. 
     According to an embodiment of the invention, the at least one refrigerant discharge aperture is arranged to fluidly connect the annular volume and the distal chamber. 
     According to an embodiment of the invention, the drive shaft extends across the orbiting scroll arrangement and further includes a first guided portion and second guided portion located on either side of the driving portion, the scroll compressor further including guide elements for guiding in rotation the drive shaft, the guide elements comprising at least one first guide bearing and at least one second guide bearing located on either side of the orbiting scroll arrangement and arranged to respectively guide the first and second guided portions of the drive shaft. 
     In other words, the orbiting scroll arrangement comprises a first side facing toward the first guided portion of the drive shaft and the at least one first guide bearing, and a second side opposite to the first side and facing toward the second guided portion of the drive shaft and the at least one second guide bearing. 
     Such a location of the first and second guide bearings reduces the drive shaft deflection. The reduction of the drive shaft deflection at the guide bearings locations improves the guide bearings reliability. Moreover, the reduction of the drive shaft deflection at the rotor location avoids on one hand the rotor-stator contacts in the driving motor and thus improves the driving motor reliability, and reduces on the other hand the mechanical loads applied on the guide bearings and thus further improves the guide bearings reliability. Furthermore the reduction of the drive shaft deflection at the rotor location allows reducing the motor air gap and so improves the driving motor performances. 
     All these improvements allow to operate the scroll compressor safely in the whole operating speed range and notably at high rotational speeds (that is at a rotation speed much higher than 9000 rpm), and improve compressor reliability and performance. 
     According to an embodiment of the invention, the drive shaft further includes a rotor support portion on which is mounted the rotor, the guide elements being located on a same side of the drive shaft in relation to the rotor support portion. 
     According to an embodiment of the invention, the rotor support portion forms a first end portion of the drive shaft. The rotor support portion may for example be set back from the second winding head of the stator. 
     According to an embodiment of the invention, the rotor includes a first rotor end portion directed towards the first fixed scroll and a second rotor end portion opposite to the first rotor end portion, the rotor support portion being set back from the second rotor end portion. 
     According to an embodiment of the invention, the scroll compressor further includes a first counterweight and a second counterweight connected to the drive shaft, the first and second counterweights being located respectively on either side of the orbiting scroll arrangement. In other words, the first and second sides of the orbiting scroll arrangement face toward respectively the first and second counterweights. This arrangement of the first and second counterweights allows to balance the mass of the orbiting scroll arrangement with a limited tilting of the drive shaft. Such a limited tilting of the drive shaft, as the reduction of the deflection of the drive shaft, improves the guide bearings reliability and the driving motor reliability, and therefore the compressor reliability and performance. 
     According to an embodiment of the invention, the drive shaft and at least one of the first and second counterweights are formed as a one-piece element. 
     According to an embodiment of the invention, the scroll compressor further includes:
         a first Oldham coupling provided between the orbiting scroll arrangement and the first fixed scroll, and configured to prevent rotation of the orbiting scroll arrangement with respect to the first fixed scroll, the first Oldham coupling being slidable with respect to the first fixed scroll along a first displacement direction,   a second Oldham coupling provided between the orbiting scroll arrangement and the second fixed scroll, and configured to prevent rotation of the orbiting scroll arrangement with respect to the second fixed scroll, the second Oldham coupling being slidable with respect to the second fixed scroll along a second displacement direction which is transverse with respect to the first displacement direction.       

     Due to the transverse movements of the first and second Oldham couplings, the centers of gravity of the first and second Oldham couplings can be assimilated to a rotating mass, which can be easily balanced by a rotating counterweight attached to the drive shaft. Therefore, compressor vibrations generated by the translation movements of the first and second Oldham couplings can be greatly reduced. Such a limitation of the compressor vibrations leads to an improvement of the compressor reliability and efficiency. 
     According to an embodiment of the invention, the second displacement direction is substantially orthogonal to the first displacement direction. For example, the first and second displacement directions of said first and second Oldham couplings may be orthogonal with respect to each other, or may be inclined by an angle comprised between 80 and 100°, and preferably between 85 and 95°. 
     According to an embodiment of the invention, the first and second displacement directions are substantially perpendicular to the rotation axis of the drive shaft. 
     According to an embodiment of the invention, each of the first and second Oldham couplings undergoes a reciprocating motion respectively along the first and second displacement directions. 
     According to an embodiment of the invention, the first and second Oldham couplings respectively include first and second annular bodies that are substantially parallel to each other. 
     According to an embodiment of the invention, the first Oldham coupling includes:
         a first annular body,   a first pair of first guiding grooves provided on the first annular body, the first guiding grooves of the first Oldham coupling slidably receiving a first pair of first engaging projections provided on the first fixed scroll, said first guiding grooves being offset and extending substantially parallel to the first displacement direction, and   a second pair of second guiding grooves provided on the first annular body, the second guiding grooves of the first Oldham coupling slidably receiving a second pair of second engaging projections provided on the orbiting scroll arrangement, said second guiding grooves being offset and extending substantially perpendicularly to the first displacement direction.       

     According to an embodiment of the invention, the first annular body is disposed around the first fixed spiral wrap and the first orbiting spiral wrap. 
     According to another embodiment of the invention, the first pair of first engaging projections may be provided on the first annular body, and the first pair of first guiding grooves may be provided on the first fixed scroll. 
     According to another embodiment of the invention, the second pair of second engaging projections may be provided on the first annular body, and the second pair of second guiding grooves may be provided on the orbiting scroll arrangement. 
     According to an embodiment of the invention, the second Oldham coupling includes:
         a second annular body,   a first pair of first guiding grooves provided on the second annular body, the first guiding grooves of the second Oldham coupling slidably receiving a first pair of first engaging projections provided on the second fixed scroll, said first guiding grooves being offset and extending substantially parallel to the second displacement direction, and   a second pair of second guiding grooves provided on the second annular body, the second guiding grooves of the second Oldham coupling slidably receiving a second pair of second engaging projections provided on the orbiting scroll arrangement, said second guiding grooves being offset and extending substantially perpendicularly to the second displacement direction.       

     According to another embodiment of the invention, the first pair of first engaging projections may be provided on the second annular body, and the first pair of first guiding grooves may be provided on the second fixed scroll. 
     According to another embodiment of the invention, the second pair of second engaging projections may be provided on the second annular body, and the second pair of second guiding grooves may be provided on the orbiting scroll arrangement. 
     According to an embodiment of the invention, the scroll compressor is a vertical scroll compressor and the drive shaft extends substantially vertically. The driving motor may be located above the scroll compression unit. 
     According to an embodiment of the invention, the scroll compressor further includes a refrigerant suction element for supplying the inner volume with refrigerant to be compressed. 
     According to an embodiment of the invention, the refrigerant suction element is sealingly connected to the inner volume. The refrigerant suction element may for example include an end portion emerging in the inner volume. Therefore, the refrigerant enters the inner volume without cooling down beforehand the driving motor and thus without being heated by the driving motor, which also improves the driving motor efficiency. 
     According to an embodiment of the invention, the scroll compression unit comprises a connecting portion delimited at least in part by at least one of the first and second fixed scrolls, the connecting portion emerging in the inner volume, the end portion of the refrigerant suction element being sealingly mounted into the connecting portion. 
     According to an embodiment of the invention, the scroll compressor further includes a refrigerant discharge element arranged for discharging the compressed refrigerant outside the scroll compressor. 
     According to an embodiment of the invention, the first and second orbiting spiral wraps are respectively provided on first and second faces of a common base plate, the second face being opposite to the first face. 
     According to an embodiment of the invention, the drive shaft comprises at least one lubrication channel connected to an oil sump of the scroll compressor and extending over at least a part of the length of the drive shaft. 
     According to an embodiment of the invention, the drive shaft further comprises at least a first lubrication hole and a second lubrication hole each fluidly connected to a respective lubrication channel, the first and second lubrication holes opening respectively into an outer wall of the first and second guided portions of the drive shaft. 
     According to an embodiment of the invention, the closed container defines a high pressure discharge volume containing the driving motor. Advantageously, refrigerant suction element is fluidly isolated from the high pressure discharge volume. The scroll compression unit may also be contained in the high pressure discharge volume. 
     The refrigerant discharge element may for example emerge in the high pressure discharge volume defined by the closed container. 
     According to an embodiment of the invention, the second fixed scroll includes at least one second discharge passage arranged to conduct, in use, at least a part of the refrigerant compressed in the second compression chambers outside the inner volume. 
     According to an embodiment of the invention, the at least one second discharge passage is fluidly connected to the high pressure discharge volume and is arranged to conduct, in use, the refrigerant compressed in the second compression chambers towards the high pressure discharge volume. 
     According to an embodiment of the invention, the second fixed base plate has a first face directed towards the first fixed scroll and a second face opposite to the first face, the at least one second discharge passage emerging in the second face of the second fixed base plate. 
     According to an embodiment of the invention, the at least one second discharge passage is inclined relative to the rotation axis of the drive shaft. 
     According to an embodiment of the invention, the at least one second discharge passage is fluidly connected to the central second compression chamber, and is arranged to conduct the refrigerant compressed in the central second compression chamber outside the inner volume. 
     According to an embodiment of the invention, the second fixed scroll and the drive shaft define a second annular chamber fluidly connected to the central second compression chamber, the at least one second discharge passage being fluidly connected to the second annular chamber, and advantageously emerging in the second annular chamber. 
     According to an embodiment of the invention, the second fixed scroll includes a plurality of second discharge passages. The second discharge passages may be for example angularly offset from each other in relation to the rotation axis of the drive shaft. 
     According to an embodiment of the invention, the scroll compressor is a variable-speed scroll compressor. 
     According to an embodiment of the invention, the first and second fixed scrolls are fixed in relation to the closed container. 
     According to an embodiment of the invention, the orbiting scroll arrangement is made in light material, such as aluminum alloy. 
     The communicating hole may for example emerge respectively in the central first and second compression chambers. 
     According to an embodiment of the invention, the scroll compressor is arranged such that at least a part of the refrigerant compressed in the central second compression chamber is conducted to the at least one first discharge passage via the communicating hole. These provisions improve the cooling of the driving motor. 
     These and other advantages will become apparent upon reading the following description in view of the drawing attached hereto representing, as non-limiting examples, embodiments of a scroll compressor according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of one embodiment of the invention is better understood when read in conjunction with the appended drawings being understood, however, that the invention is not limited to the specific embodiment disclosed. 
         FIGS. 1 and 2  are longitudinal section views of a scroll compressor according to the invention. 
         FIG. 3  is a longitudinal section view of the drive shaft of the scroll compressor of  FIG. 1 . 
         FIGS. 4 and 5  are exploded perspective views of two Oldham couplings and of an orbiting scroll arrangement of the scroll compressor of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a vertical scroll compressor  1  including a closed container  2  defining a high pressure discharge volume, and a scroll compression unit  3  disposed inside the closed container  2 . 
     The scroll compression unit  3  includes first and second fixed scrolls  4 ,  5  defining an inner volume  6 . In particular the first and second fixed scrolls  4 ,  5  are fixed in relation to the closed container  2 . The first fixed scroll  4  may for example be secured to the second fixed scroll  5 . The scroll compression unit  3  further includes an orbiting scroll arrangement  7  disposed in the inner volume  6 . 
     The first fixed scroll  4  includes a base plate  8  and a spiral wrap  9  projecting from the base plate  8  towards the second fixed scroll  5 , and the second fixed scroll  5  includes a base plate  11  and a spiral wrap  12  projecting from the base plate  11  towards the first fixed scroll  4 . 
     The orbiting scroll arrangement  7  includes a base plate  13 , a first spiral wrap  14  projecting from a first face of the base plate  13  towards the first fixed scroll  4 , and a second spiral wrap  15  projecting from a second face of the base plate  13  towards the second fixed scroll  5 , the second face being opposite to the first face such that the first and second spiral wraps  14 ,  15  project in opposite directions. The first and second fixed scrolls  4 ,  5  are respectively located above and below the orbiting scroll arrangement  7 . 
     The first spiral wrap  14  of the orbiting scroll arrangement  7  meshes with the spiral wrap  9  of the first fixed scroll  4  to form a plurality of compression chambers  16  between them, and the second spiral wrap  15  of the orbiting scroll arrangement  7  meshes with the spiral wrap  12  of the second fixed scroll  5  to form a plurality of compression chambers  17  between them. Each of the compression chambers  16 ,  17  has a variable volume which decreases from the outside towards the inside, when the orbiting scroll arrangement  7  is driven to orbit relative to the first and second fixed scrolls  4 ,  5 . 
     The orbiting scroll arrangement  7  includes at least one communicating hole  18  arranged to fluidly connect the central compression chamber  16  and the central compression chamber  17 . The communicating hole  18  may for example emerge respectively in the central first and second compression chambers  16 ,  17 . 
     The scroll compressor  1  also includes a refrigerant suction pipe  19  communicating with the inner chamber  6  to achieve the supply of refrigerant to the scroll compression unit  3 , and a refrigerant discharge pipe  20  for discharging the compressed refrigerant outside the scroll compressor  1 . The refrigerant suction pipe  19  may for example be sealingly connected to the inner volume  6 . The refrigerant discharge pipe  20  may for example emerge in the high pressure discharge volume. 
     The first fixed scroll  4  includes a plurality of discharge passages  21  fluidly connected to the high pressure discharge volume and arranged to conduct the refrigerant compressed in the compression chambers  16  outside the inner volume  6 . 
     The second fixed scroll  5  also includes a plurality of discharge passage  22  fluidly connected to the high pressure discharge volume and arranged to conduct the refrigerant compressed in the compression chambers  17  outside the inner volume  6 . 
     Furthermore the scroll compressor  1  includes a stepped drive shaft  23  adapted for driving the orbiting scroll arrangement  7  in orbital movements, an electric driving motor  24  coupled to the drive shaft  23  and arranged for driving in rotation the drive shaft  23  about a rotation axis, and an intermediate casing  25  fixed on the first fixed scroll  4  and in which the driving motor  24  is entirely mounted. 
     Each discharge passage  21  is provided in the base plate  8  of the first fixed scroll  4 , and includes a first end portion emerging in an annular chamber C 1  defined by the first fixed scroll  4  and the drive shaft  23  and fluidly connected to the central compression chamber  16 , and a second end portion emerging outside the inner volume  6 . Each discharge passage  22  is provided in the base plate  11  of the second fixed scroll  5 , and includes a first end portion emerging in an annular chamber C 2  defined by the second fixed scroll  5  and the drive shaft  23  and fluidly connected to the central compression chamber  17 , and a second end portion emerging outside the inner volume  6  towards an oil sump defined by the closed container  2 . 
     The driving motor  24 , which may be a variable-speed electric motor, is located above the first fixed scroll  4 . The driving motor  24  has a rotor  26  fitted on the drive shaft  23 , and a stator  27  disposed around the rotor  26 . The stator  27  includes a stator stack or stator core  28 , and stator windings wound on the stator core  28 . The stator windings define a first winding head  29   a  which is formed by the portions of the stator windings extending towards outside from the end face  28   a  of the stator core  28  oriented towards the scroll compression unit  3 , and a second winding head  29   b  which is formed by the portions of the stator windings extending towards outside from the end face  28   b  of the stator core  28  opposite to the scroll compression unit  3 . 
     As shown in  FIG. 1 , the intermediate casing  25  and the closed container  2  define an annular outer volume  31  fluidly connected to the discharge pipe  20 . Further the intermediate casing  25  and the driving motor  24  define a proximal chamber  32  containing the first winding head  29   a  of the stator  27 , and a distal chamber  33  containing the second winding head  29   b  of the stator  27 . 
     The intermediate casing  25  is provided with a plurality of refrigerant discharge apertures  34  emerging in the distal chamber  33  and arranged to fluidly connect the distal chamber  33  and the annular outer volume  31 . According to the embodiment shown on the figures, the intermediate casing  25  includes a side part  25   a  surrounding the stator  27  and a closing part  25   b  closing an end portion of the side part  25   a  opposite to the first fixed scroll  4 . 
     According to the embodiment shown on the figures, the second end portion of each discharge passages  21  emerges in the proximal chamber  32  nearby the driving motor  24 , and particularly nearby the first winding head  29   a  of the stator  27 . Advantageously, each of the discharge passages  21 ,  22  is inclined relative to the rotation axis of the drive shaft  23 . 
     The drive shaft  23  extends vertically across the base plate  13  of the orbiting scroll arrangement  7 . The drive shaft  23  comprises a first end portion  35  located above the first fixed scroll  4  and on which is fitted the rotor  26 , and a second end portion  36  opposite to the first end portion  35  and located below the second fixed scroll  5 . The first end portion  35  has an external diameter larger than the external diameter of the second end portion  36 . The first end portion  35  includes a central recess  37  emerging in the end face of the drive shaft  23  opposite to the second end portion  36 . 
     The drive shaft  23  further comprises a first guided portion  38  and a second guided portion  39  located between the first and second end portion  35 ,  36 , and an eccentric driving portion  41  located between the first and second guided portions  38 ,  39  and being off-centered from the center axis of the drive shaft  23 . The eccentric driving portion  41  is arranged to cooperate with the orbiting scroll arrangement  7  so as to cause the latter to be driven in an orbital movement relative to the first and second fixed scrolls  4 ,  5  when the driving motor  24  is operated. 
     The scroll compressor  1  further comprises guide elements for guiding in rotation the drive shaft  23  about its rotation axis. The guide elements comprise at least one first guide bearing  42  provided on the first fixed scroll  4  and arranged for guiding the first guided portion  38  of the drive shaft  23 , and one second guide bearing  43  provided on the second fixed scroll  5  and arranged for guiding the second guided portion  39  of the drive shaft  23 . According to the embodiment shown on the figures, the guide elements comprise two first guide bearings  42  provided on the first fixed scroll  4  and arranged for guiding the first guided portion  38  of the drive shaft  23 . 
     It should be noted that the guide bearings  42 ,  43  are located on a same side of the drive shaft  23  in relation to the first end portion  35 . 
     The scroll compressor  1  further comprises at least one bearing  44  provided on the orbiting scroll arrangement  7  and arranged for cooperating with the eccentric driving portion  41  of the drive shaft  23 . According to the embodiment shown on the figures, the scroll compressor  1  comprises two bearings  44  provided on the orbiting scroll arrangement  7  and arranged for cooperating with the eccentric driving portion  41  of the drive shaft  23 . 
     The drive shaft  23  further comprises a first and a second lubrication channels  45 ,  46  extending over a part of the length of the drive shaft  23  and arranged to be supplied with oil from the oil sump defined by the closed container  2 , by an oil pump  47  driven by the second end portion  36  of the drive shaft  23 . 
     According to the embodiment shown on the figures, the first and second lubrication channels  45 ,  46  are substantially parallel to the center axis of the drive shaft  23  and off-centered from the center axis of the drive shaft  23 . However, according to another embodiment of the invention, the first and second lubrication channels  45 ,  46  may be inclined relative to the center axis of the drive shaft  23 . 
     According to the embodiment shown on the figures, the oil pump  47  is made of a pump element having a substantially cylindrical connecting portion connected to the second end portion  36  of the drive shaft  23  and an end portion having a curved shape and provided with an oil opening. However, according to another embodiment of the invention, the oil pump  47  may be made of the second end portion  36  of the drive shaft  23 . 
     The drive shaft  23  also comprises at least one first lubrication hole  48  fluidly connected to the first lubrication channel  45  and opening into an outer wall of the first guided portion  38  of the drive shaft  23 , at least one second lubrication hole  49  fluidly connected to the second lubrication channel  46  and opening into an outer wall of the second guided portion  39  of the drive shaft  23 , and at least one third lubrication hole  51  fluidly connected to the first lubrication channel  45  and opening into an outer wall of the eccentric driving portion  41  of the drive shaft  23 . Advantageously, each of the first, second and third lubrication holes extends substantially radially relative to the drive shaft  23 . 
     According to the embodiment shown on the figures, the drive shaft  23  comprises two first lubrication holes  48 , one second lubrication hole  49  and two third lubrication holes  51 , each first lubrication hole  48  facing one guide bearing  42 , and each third lubrication hole  51  facing one bearing  44 . According to an embodiment not shown on the figures, the drive shaft  23  may comprise only one third lubrication hole  51  located between the bearings  44 . 
     The drive shaft  23  may further comprise a vent hole  52  fluidly connected on the one hand to the first lubrication channel  45  and on the other hand to the central recess  37  of the first end portion  35  of the drive shaft  23 . The vent hole  52  may for example extend substantially radially relative to the drive shaft  23 . 
     The drive shaft  23  may further comprise a communicating channel  53  arranged to fluidly connect the first and second lubrication channels  45 ,  46 . The communicating channel  53  ensures the degassing of the oil circulating in the second lubrication duct  46 , and the flow of the refrigerant originating from the degassing into the first lubrication duct  45  towards the vent hole  52 . 
     The scroll compressor  1  also comprises a first Oldham coupling  54  which is slidably mounted with respect to the first fixed scroll  4  along a first displacement direction D 1 , and a second Oldham coupling  55  which is slidably mounted with respect to the second fixed scroll  5  along a second displacement direction D 2  which is substantially orthogonal to the first displacement direction D 1 . The first and second displacement directions D 1 , D 2  are substantially perpendicular to the rotation axis of the drive shaft  23 . The first and second Oldham couplings  54 ,  55  are configured to prevent rotation of the orbiting scroll arrangement  7  with respect to the first and second fixed scrolls  4 ,  5 . Each of the first and second Oldham couplings  54 ,  55  undergoes a reciprocating motion respectively along the first and second displacement directions D 1 , D 2 . 
     The first Oldham coupling  54  includes an annular body  56  disposed between the base plates  8 ,  13  of the first fixed scroll  4  and the orbiting scroll arrangement  7 , and around the spiral wraps  9 ,  14 . The first Oldham coupling  54  further includes a pair of first guiding grooves  57  provided on a first side of the annular body  56 , and a pair of second guiding grooves  58  provided on a second side of the annular body  56 . The first guiding grooves  57  of the first Oldham coupling  54  slidably receive a pair of first engaging projections  59  provided on the base plate  8  of the first fixed scroll  4 , the first guiding grooves  57  being offset and extending parallel to the first displacement direction D 1 . The second guiding grooves  58  of the first Oldham coupling  54  slidably receive a pair of second engaging projections  61  provided on the base plate  13  of the orbiting scroll arrangement  7 , the second guiding grooves  58  being offset and extending parallel to the second displacement direction D 2 , i.e. perpendicularly to the first displacement direction D 1 . 
     The second Oldham coupling  55  includes an annular body  62  disposed between the base plates  11 ,  13  of the second fixed scroll  5  and the orbiting scroll arrangement  7 . The annular body  62  of the second Oldham coupling  55  extends substantially parallel to the annular body  56  of the first Oldham coupling  54 . 
     The second Oldham coupling  55  further includes a pair of first guiding grooves  63  provided on a first side of the annular body  62 , and a pair of second guiding grooves  64  provided on a second side of the annular body  62 . The first guiding grooves  63  of the second Oldham coupling  55  slidably receive a pair of first engaging projections  65  provided on the second fixed scroll  5 , the first guiding grooves  63  being offset and extending parallel to the second displacement direction D 2 . The second guiding grooves  64  of the second Oldham coupling  55  slidably receive a pair of second engaging projections  66  provided on the base plate  13  of the orbiting scroll arrangement  7 , the second guiding grooves  64  being offset and extending parallel to the first displacement direction D 1 , i.e. perpendicularly to the second displacement direction D 2 . 
     The scroll compressor  1  further includes a first counterweight  67  and a second counterweight  68  connected to the drive shaft  23 , and arranged to balance the mass of the orbiting scroll arrangement  7 . The first counterweight  67  is located above the first fixed scroll  4 , and the second counterweight  68  is located below the second fixed scroll  5 . 
     According to the embodiment shown on the figures, the first counterweight  67  and the drive shaft  23  are formed as a one-piece element, and the second counterweight  68  is distinct from the drive shaft  23  and is attached to the latter. For example, the first counterweight  67  may be formed by removing material from the drive shaft  23 . 
     In operation, a first part of the refrigerant entering in the inner volume  6  through the refrigerant suction pipe  19  is compressed into the compression chambers  16  and escapes from the centre of the first fixed scroll  4  and of the orbiting scroll arrangement  7  through the discharge passages  21  leading to the proximal chamber  32 . The compressed refrigerant entering in the proximal chamber  32  then flows upwardly towards the distal chamber  33  by passing through refrigerant flow passages delimited by the stator  27  and the intermediate casing  25  and through gaps delimited between the stator  27  and the rotor  26 . Next, the compressed refrigerant travels through the refrigerant discharge apertures  34  leading to the annular outer volume  31 , from which the compressed refrigerant is discharged by the discharge pipe  20 . 
     Thus the compressed refrigerant coming out of the discharge passages  21  cools down the first winding head  29   a , the compressed refrigerant passing through the refrigerant flow passages cools down the stator core  28 , the refrigerant passing through the gaps cools down the stator core  28 , the stator windings and the rotor  26 , while the compressed refrigerant coming out of the refrigerant flow passages and of the gaps cools down the second winding head  29   b . Such a cooling down of the driving motor  24  protects the stator  27  and the rotor  26  against damage and improves the efficiency of the scroll compressor  1 . 
     In operation, a second part of the refrigerant entering in the inner volume  6  through the refrigerant suction pipe  19  is compressed into the compression chambers  17  and escapes from the centre of the second fixed scroll  5  and of the orbiting scroll arrangement  7  partially through the communicating hole  18  and the discharge passages  21 , and partially through the discharge passages  22  leading to the high pressure discharge volume. Therefore, a first part of the refrigerant compressed in the compression chambers  17  is discharged by the refrigerant discharge pipe  20  without cooling down the driving motor  24 , and a second part of the refrigerant compressed in the compression chambers  17  is discharged by the refrigerant discharge pipe  20  after having cooling down the driving motor. 
     It should be noted that the configuration of the discharge passages  21 ,  22  allow to balance the pressure in the oil sump on the one hand, and the pressure in the space in which emerges the refrigerant discharge pipe  20  on the other hand. Such a pressure balance avoids the “oil cleaning” of the several bearings by the refrigerant. 
     Of course, the invention is not restricted to the embodiments described above by way of non-limiting examples, but on the contrary it encompasses all embodiments thereof.