Abstract:
In order to improve a compressor comprising a scroll compressor with a first compressor member and a second compressor member, a drive with a drive motor and an entraining unit which has an entraining member moving on an entraining path and an entraining member receiving means arranged on the second compressor member, wherein the compressor member receiving means is movable in a radial direction in relation to the central axis with a radial degree of freedom in relation to the entraining member, in such a manner that this can be produced as simply as possible and operates as reliably as possible it is suggested that the entraining member have an entraining member surface curved convexly in a direction transverse to the central axis in a direction of rotation, that the entraining member receiving means be non-rotatably arranged in relation to the second compressor member and have an entraining surface which surrounds the entraining member in a ring shape and on which the entraining member surface bears by always acting upon it with a force only in an orbiting subsection and that a space exist between the entraining member and the entraining surface outside the subsection acted upon with a force.

Description:
The present disclosure relates to the subject matter disclosed in International Application No. PCT/EP00/01451 of Feb. 23, 2000, the entire specification of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a compressor comprising a scroll compressor with a first compressor member and a second compressor member, first and second scroll ribs, respectively, of which are designed in the form of a circular involute and engage in one another such that the second compressor member can be moved in relation to the first compressor member on an orbital path about a central axis, a drive for the scroll compressor with a drive motor and an entraining unit which has an entraining member driven by the drive motor and moving on an entraining path about the central axis and an entraining member receiving means arranged on the second compressor member, wherein the entraining member receiving means can be moved in a radial direction in relation to the central axis with a radial degree of freedom in relation to the entraining member such that the second compressor member can be moved so as to abut sealingly with the second scroll rib on the first scroll rib of the first compressor member on account of the radial degree of freedom and the centrifugal forces acting on the second compressor member. 
     A scroll compressor of this type is known, for example, from U.S. Pat. No. 5,295,813. 
     The problem with these scroll compressors is that this solution is complicated to produce and, on the other hand, undesired, high, local area pressures can occur due to the flat entraining member surfaces. 
     SUMMARY OF THE INVENTION 
     The object underlying the invention is therefore to improve a compressor of the generic type in such a manner that this can be produced as simply as possible and operates as reliably as possible. 
     This object is accomplished in accordance with the invention, in a compressor of the type described at the outset, in that the entraining member has an entraining member surface curved convexly in a direction transverse to the central axis in a direction of rotation, that the entraining member receiving means is non-rotatably arranged in relation to the second compressor member and has an entraining surface which surrounds the entraining member in a ring shape and on which the entraining member surface bears by always acting upon it with a force only in a subsection, that during movement of the second compressor member on the orbital path the subsection acted upon with a force likewise moves on the entraining surface and that a space allowing the radial degree of freedom of the entraining member receiving means in relation to the entraining member exists between the entraining member and the entraining surface outside the subsection acted upon with a force. 
     The advantage of the inventive solution lies in its constructional simplicity which allows the entraining member receiving means, on the one hand, to be arranged on the second compressor member so as to no longer be rotatable but rather non-rotatable so that the rotary bearing required for this can be omitted since in the inventive solution the relative rotation is accomplished by the movement of the subsection on the entraining surface. 
     In addition, the inventive solution has the great advantage that it requires less parts and, in particular, only parts which are easy to machine. 
     A particularly simple solution from a constructional point of view provides for the entraining member receiving means to be securely arranged on the second compressor member. 
     In the constructionally simplest case, this is a bushing which is preferably integrally formed on the compressor member, the entraining member engaging in its inner recess. 
     With respect to the dimensioning of the possible radial degree of freedom it would also be conceivable to design this to be smaller than the maximum possible movements of the compressor member in a radial direction. It is, however, particularly favorable when the possible radial degree of freedom corresponds at least to the maximum deviation of the orbital path of the second compressor member from a geometrical circular path around the central axis. In this respect, the geometrical circular path around the central axis represents the ideal case of the orbital path which cannot, however, either be achieved from time to time or be maintained over a longer period on account of the manufacturing inaccuracies in the area of the scroll ribs, on account of thermal changes during operation, for example, varying temperature expansion or also on account of wear and tear and so it is to be assumed that the actual orbital path of the second compressor member deviates from the ideal geometrical circular path. 
     With respect to the dimensioning of the space it is particularly favorable when the space has in a radial direction an extension which corresponds at least to the maximum deviation of the orbital path from the geometrical circular path since, as a result, the space is in a position to allow the radial movements which are necessary so that the second compressor member always extends with its second scroll rib so as to lie along the first scroll rib of the first compressor member. 
     In a preferred embodiment the space has a dimension which is in the range of approximately 1.5‰ to approximately 15‰ of an extension of the entraining surface in a respective radial direction. Values of approximately 2‰ to approximately 10‰ are preferred. 
     With respect to the design of the space the most varied of solutions are conceivable. It would, for example, be conceivable for the space to become suddenly wider following the entraining member surface. 
     However, in order to provide for the fact that during a radial movement of the entraining member receiving means relative to the entraining member the radial movement is subject to a certain attenuation, it is preferably provided for the distance between them proceeding from the subsection acted upon with a force to become increasingly larger with increasing distance from the subsection, i.e. due to the continuous increase in the distance between the entraining member surface and the entraining surface a lubricant cushion forms close to the subsection acted upon with a force and this has to be expelled from the space during a sudden radial movement and thus a certain attenuation effect begins. 
     In this respect it is particularly favorable when the distance between the entraining member surface and the entraining surface on both sides of the subsection acted upon with a force increases with increasing distance from it so that a movement in a radial direction and also in the opposite direction thereto experiences a respective attenuation. 
     A particularly favorable solution with respect to the production of the entraining surface provides for the entraining surface to extend in a circular shape, preferably as a cylinder surface of a circular cylinder, so that during the movement of the second compressor member on the orbital path the entraining member surface moves along the entraining surface extending in a circular or cylindrical manner. 
     In this respect, the center point of the circle or cylinder formed by the entraining surface is preferably located on the circular path around the central axis which underlies the orbital path. 
     With respect to the design of the entraining unit, no further details have been given in conjunction with the preceding explanations concerning the invention. A most simple embodiment of an inventive entraining unit provides for this to have a single entraining member surface and an entraining surface associated with it. The space is preferably located between the entraining member and the entraining surface. 
     Another advantageous solution provides for the entraining surface associated with the entraining member surface to be arranged on an intermediate ring which, for its part, bears with an additional entraining member surface on an additional subsection of an additional entraining surface by acting upon it with a force and for an additional space contributing to the radial degree of freedom of the entraining member receiving means in relation to the entraining member to likewise exist between the intermediate ring and the additional entraining surface. The advantage of this solution is to be seen in the fact that it is possible to divide the radial degree of freedom which can be obtained altogether between at least two or more spaces so that these spaces can, for their part, be kept as small as possible in order to achieve as good a lubrication as possible in the area of the spaces but, on the other hand, the radial degree of freedom possible altogether in a radial direction can be as large as possible on account of the sum of the widths of the spaces in a radial direction. 
     With this embodiment it is not absolutely necessary for the intermediate ring to slide along the additional entraining surface with the additional entraining member surface. It is also conceivable for the intermediate ring to roll on the additional entraining surface with the additional entraining member surface. 
     As for the rest, it is also conceivable within the scope of the inventive solution for the entraining member surface to roll on the entraining surface even with only one entraining member surface and one associated entraining surface which does, however, make it necessary to realize the entraining member surface, for example, as an outer surface of a sleeve surrounding the entraining member and rotatably mounted on it so that the entraining member surface can, as entire outer surface of the sleeve, roll on the associated entraining surface during the movement of the second compressor member on the orbital path. 
     For reasons of as inexpensive a solution as possible it is, however, particularly favorable when at least one of the entraining member surfaces slides relative to the associated entraining surface during the movement of the second compressor member on the orbital path since this solution is particularly simple to realize and also allows a large degree of freedom with respect to the design of the member bearing this entraining member surface. 
     In the case of an entraining member surface sliding on the entraining surface it is important to have an optimum lubrication which can be obtained when a hydrodynamic lubrication film can be generated between the sliding entraining member surface and the associated entraining surface, this film contributing to the fact that no essentially linear abutment takes place between the entraining member surface and the entraining surface but rather the entraining member surface bears over an area with a greater expansion on account of the lubrication film. 
     For the formation of such a lubrication film it is particularly favorable when lubricant is supplied in front of the entraining member surface when seen in the direction of rotation of the entraining member so that the lubricant is moved during the rotary movement in the direction of the subsection acted upon with a force. 
     In this respect, it is particularly favorable when the supply of lubricant takes place via the entraining member. 
     Such a supply of lubricant to the entraining unit via the entraining member may be realized in the most varied of ways. It would be conceivable, for example, to allow lubricant to exit at the end side of the entraining member, this lubricant then moving in the direction of the space and passing into it. A particularly favorable solution provides for the entraining member to be provided for this purpose with a lubricant channel passing through it, wherein the lubricant channel preferably continues from the entraining member via the drive shaft and a lubricant pump is arranged, for example, at an end of the drive shaft of the drive motor located opposite the entraining member. 
     In order to achieve a particularly precise lubrication, it is preferably provided for the entraining member to be provided with a lubricant outlet opening opening near to the entraining member surface and into the space so that the lubricant is preferably introduced into the space directly in front of the entraining member surface and then moves from the space in the direction of the subsection acted upon with a force. 
     With respect to the design of the space, the most varied of possibilities are conceivable. However, in order to have the lubricant available in the area of the subsection acted upon with a force in as optimum a manner as possible, particularly for forming a hydrodynamic lubrication film, it is preferably provided for the space to have in front of the entraining surface when seen in the direction of rotation of the entraining member an extension which holds the lubricant on account of a capillary action. 
     It is even better when the space has over its entire extent such an extension that it holds lubricant on account of a capillary action. 
     With respect to the alignment of the entraining member surface in relation to the direction, in which the radial degree of freedom is effective, particularly in the direction of a connection line between the central axis and a contact line of the scroll ribs, no further details have so far been given. 
     It is, for example, particularly advantageous when the subsection of the entraining surface acted upon with a force always extends approximately parallel to the direction of the radial degree of freedom and retains this alignment so that, as a result, a defined alignment of the effect of the entraining member on the entraining member receiving means can be determined. In the ideal case, the subsection lies symmetrically to a tangent to the circular path underlying the orbital path, wherein the tangent extends through the center point of the circular entraining surface. In this case, the entraining member always acts on the second compressor member in such a manner that it is in a position to overcome the tangential gas force but does not make any contribution whatsoever towards the radial degree of freedom and so the radial gas force merely counteracts the centrifugal force. 
     It is, however, also conceivable to determine the subsection of the entraining surface acted upon with a force such that this has a slight inclination in relation to the direction of the radial degree of freedom and thus the fact that the tangential gas force is overcome by the entraining member leads either to an additional force component acting radially outwards in addition to the centrifugal force or to an additional force component acting radially inwards. 
     Additional features 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 an inventive compressor; 
     FIG. 2 shows an enlarged subsection along line  2 — 2  in FIG. 1 with additional illustration of a section of a first and a second scroll rib, with which overcoming of the tangential gas force does not lead to a radial force component; 
     FIG. 3 shows an illustration of a layout of the first embodiment, wherein the overcoming of the tangential gas force leads to a force component in a radial direction; 
     FIG. 4 shows a section similar to FIG. 1 through a second embodiment of an inventive compressor; 
     FIG. 5 shows a section similar to FIG.  2  through the second embodiment; 
     FIG. 6 shows a section similar to FIG. 2 through a third embodiment of an inventive compressor. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One embodiment of an inventive scroll compressor, illustrated in FIG. 1, comprises a housing which is designated as a whole as  10  and in which an electric drive motor designated as a whole as  12  and a scroll compressor designated as a whole as  14  are arranged. 
     The scroll compressor comprises a first compressor member  16  and a second compressor member  18 , wherein the first compressor member  16  has a first scroll rib  22  designed in the form of a circular involute and rising above a base surface  20  of the first compressor member and the second compressor member  18  has a scroll rib  26  designed in the form of a circular involute and rising above a base surface  24 , wherein the scroll ribs  22 ,  26  engage in one another and thereby abut sealingly on the respective base surface  24  or  20  of the respectively other compressor member  18 ,  16  so that chambers  27  are formed between the scroll ribs  22 ,  26  as well as the base surfaces  20 ,  24  and in these chambers a compression of a medium takes place which flows in with initial pressure via an inlet chamber  30  surrounding the scroll ribs  22 ,  26  radially outwards and after the compression in the chambers  27  exits via an outlet  32 , provided in the first compressor member  16 , with an end pressure. 
     In the first embodiment as described, the first compressor member  16  is held securely in the compressor housing  10  whereas the second compressor member  18  is movable about a central axis  34  on an orbital path  36  relative to the first compressor member  16 , wherein the scroll ribs  22  and  26  theoretically abut on one another along a contact line  28  and the contact line  28  likewise moves about the central axis  34  on the orbital path  36  during the movement of the second compressor member  18 . 
     The drive motor  12  for driving the second compressor member  18  comprises a stator  40  which is securely arranged in the housing  10  and a rotor  42  which is seated on a drive shaft  44  which, for its part, is mounted in the housing  10  so as to be rotatable, namely about the axis  34 . 
     To couple the rotary movement of the drive shaft  44  to the second compressor member  18 , an entraining unit designated as a whole as  50  is provided and this comprises an eccentric  52  designed as an entraining member which is arranged so as to be offset in relation to the central axis  34 , namely in a radial direction. 
     The entraining member  52  engages in an entraining member receiving means  54  which is designed as a bushing and arranged on a base part  56  of the second compressor member  18 , namely on a side thereof located opposite the scroll rib  26  and points in the direction of the drive motor  12 . 
     As illustrated in FIG. 2, the entraining member receiving means  54  designed as a bushing has an inner cylinder surface  60 , the cylinder axis  62  of which, on the one hand, intersects the theoretically circular orbital path  36 , on the other hand, extends parallel to the central axis  34  but is arranged so as to be offset in relation to the central axis  34  by the radius of the orbital path  36 . 
     The entraining member  52  designed as an eccentric is, for its part, likewise preferably designed as a cylindrical member with a cylinder casing surface  64 , the cylinder axis  66  of which likewise extends parallel to the central axis  34  and, in addition, has a radial distance RE from it which corresponds approximately to the radius of the orbital path  36 . 
     In accordance with the invention, the entraining member  52  is designed such that it abuts with an entraining member surface  70  on the inner cylinder surface  60  of the entraining member receiving means  54  acting as entraining surface in a subsection  72  thereof but, for the rest, extends without contact in relation to the entraining surface  60  so that proceeding from the subsection  72  a space  74  results between the entraining member  52  and the entraining member receiving means  54  which, first of all, adjoining the subsection  72  has areas  76  and  78 , in which a width of the space becomes increasingly larger, and, with increasing width of the space  74 , these areas  76  and  78  merge into an area  80  of maximum width, wherein the area  80  is, in the first embodiment, located opposite the subsection  72 . 
     During the movement of the entraining member  52  about the central axis  34  in the direction of rotation  82 , the entraining member surface  70  acts with a force A against the subsection  72  of the entraining surface  60  in order to overcome the tangential gas force TG. In an initial position, in which the cylinder axis  62  moves on the theoretically provided circular orbital path  36  about the central axis, the tangential gas force TG aligned in a direction  84  of a tangent to the orbital path  36  through the cylinder axis  62  acts in a neutral direction which, on the one hand, extends through the cylinder axis  66  as a curvature center point of the entraining member surface  70  and, on the other hand, extends through the cylinder axis  62  and is at right angles to a straight line  86  which connects the central axis  34  with the contact line  28  of the scroll ribs  22 ,  26 . Since, in the initial position, a tangent  85 , applied to the entraining member surface  70  in the subsection  72  at the point of intersection with the tangent  84  to the orbital path  36 , extends parallel to the straight line  86  and thus parallel to the radial direction, the drive force A and the tangential gas force TG cancel one another without generating a force component effective in a radial direction to the central axis  34  and so the radial gas force RG acting on the second compressor member  18  in the area of the contact line  28  and in the direction of the connecting straight line  86  can be compensated exclusively by the centrifugal force Z which is likewise effective in the direction of the connecting straight line  86  in the area of the contact line  28 . 
     Such a dimensioning makes it necessary to select the distance RE of the cylinder axis  66  of the entraining member  52  from the central axis  34  to be larger than the radius RB of the orbital path  36  since the cylinder axis  66  is offset in relation to the cylinder axis  62  in the direction of the subsection  72  acted upon with a force. 
     However, there is also the possibility, as illustrated in FIG. 3, of having the tangential gas force TG act such that a component TGR effective in the radial direction  86  results. This case occurs when the cylinder axis  62  of the cylinder surface  60  is displaced either in the direction of the central axis  34  or away from it in relation to the initial position (FIG.  2 ), in which the cylinder axis  66  is located on the tangent  84 . If, for example, as illustrated in FIG. 3, the cylinder axis  62  is displaced in relation to the cylinder axis away from the central axis  34  when seen in radial direction  86  and is thus located, in relation to the radial direction  86 , on the side of the cylinder axis  66  located opposite the central axis  34 , the subsection  72 ′ is located in relation to the subsection  72  in the case according to FIG. 2 such that it is displaced in the direction of the central axis  34  towards it and thus the tangent  85 ′, applied in the subsection  72 ′, is inclined in relation to the radial direction  86  such that the tangential gas force TG effective parallel to the tangent  84  comprises a component TGS at right angles to the tangent  85 ′ and a component TGR in the radial direction  86  which, in the case illustrated in FIG. 3, counteracts the centrifugal force Z and has an attenuating effect in the same direction as the radial gas force RG, i.e. with respect to the force, with which the scroll ribs  22 ,  26  abut on one another. 
     Such a radial component TGR of the tangential gas force can already be determined constructionally as a result of the fact that the distance RE is selected to be smaller than it would have to be for the initial position. 
     A radial component TGR does, however, also occur when the radius RB of the orbital path  36  increases on account of machining inaccuracies in the area of the scroll ribs  22 ,  26  abutting on one another in relation to the radius RB for the initial position. 
     A radial component TGR acting in the reverse, i.e. a component TGR having an intensifying effect with respect to the force, with which the scroll ribs  22 ,  26  abut on one another, results when the cylinder axis  62  is displaced towards the central axis  34  in relation to the cylinder axis  66  and, when seen in radial direction  86 , is located between this and the cylinder axis  66 , wherein the radial component TGR having an intensifying effect may either be predetermined constructionally or result due to a change in the radius of the orbital path  36  on account of inaccuracies. 
     During the movement of the entraining member  52  on the orbital path  36  the subsection  72  of the entraining surface  60  acted upon with a force moves each time in the direction of rotation  82  on the entraining member surface  60  since the second compressor member  18  is movable radially to the central axis  34  but is held so as to be non-rotatable about it by means of a customary Oldham coupling  90  relative to the housing  10 . 
     On the other hand, the entraining member surface  70  of the entraining member  52  always remains the same since the entraining member  52  is rigidly connected to the drive shaft  44  and thus pivots about it with the central axis  34  as axis of rotation. 
     On account of the increasing width in the areas  76  and  78  of the space  74  between the entraining member  52  and the entraining member receiving means  54 , the areas  76  and  78  of the space  74  have at the point, at which these are penetrated by the connecting straight line  86 , a width W which allows a movement of the second compressor member  18  in a radial direction in relation to the central axis  34  so that, altogether, the second compressor member  18  with the scroll rib  26  has a radial degree of freedom in the direction of the line  86  which makes it possible for, on the one hand, the second scroll rib  26  to lift for a short time away from the first scroll rib  22  during the occurrence of liquid impacts and for the second scroll rib  26 , in addition, to be in a position to compensate for manufacturing inaccuracies in the area of the scroll ribs  22  and  26 , for example, on account of a lack of surface accuracies. 
     This means that with the present invention the guidance of the second compressor member  18  during the movement along the path in a radial direction is brought about by the scroll ribs  22  and  26  abutting on one another along the contact line  28  and so the orbiting movement of the second compressor member  18  does not generate, when viewed exactly, a theoretically circular orbital path  36  about the central axis  34  but rather deviates from this ideal geometrical circular path on account of manufacturing inaccuracies or heat expansions or wear and tear caused by operations. All this is compensated automatically by the second compressor member  18  on account of the centrifugal force Z acting on it since the entraining member receiving means  54  is in a position to carry out radial movements in relation to the central axis  34  on account of the width W of the space  74  in the areas  76  and  78 . 
     The width W is configured such that this is at least as large as the resulting deviations of the orbital path  36  from the ideal geometrical circular path around the central axis  34 . 
     On the other hand, it is advantageous not to make the width W too large in order to keep as small as possible any additional operating instability on account of further dynamic effects and, in particular, overshooting movements of the compressor member during liquid impacts. This is of advantage, in addition, for reasons of an optimum lubrication between the entraining member surface  70  and the entraining surface  60 . 
     In one advantageous, practical form of realization the width W has been dimensioned such that it is in the order of magnitude of the deviations of the orbital path  36  from an ideal circular path. The width W is preferably in a range of approximately 1.5‰ to approximately 15‰ of the diameter of the circle determining the cylinder inner surface  60 , preferably in the range of approximately 3‰ to approximately 10‰. In relation to a bearing clearance which would be necessary if the cylinder surface  64  of the entraining member  52  were to form a customary rotating friction bearing with the cylinder inner surface  60  of the entraining member receiving means  54 , this means that the width W is at least 1.5 times a maximum customary bearing clearance and is smaller than six times a customary maximum bearing clearance. 
     The lubrication between the entraining member surface  70  and the entraining surface  60  is brought about by an oil channel  92  which passes through the drive shaft  44  and the entraining member  52  proceeding from an oil pump  91 , ends on an end side  94  of the entraining member  52  facing away from the drive shaft  44  with an opening  96  and thus introduces oil into a chamber  98  between the end side  94  and the base plate  56  of the second compressor member  18 , this oil then entering the space  74  from this chamber  98 , wherein the space  74  is preferably dimensioned such that the oil is drawn into it by a capillary action, wherein a hydrodynamic lubrication film may be generated in the subsection  72  in a simple manner on account of the subsection  72  moving on the entraining surface  60 . 
     As for the rest, the second compressor member  18  is movable, in addition, axially in the direction of the central axis  34  towards the first compressor member and is acted upon by a piston  99  which is mounted in the housing  10  and the pressure chambers  99   a, b  of which are connected via channels to the medium to be compressed which is subject to pressure and are thus acted upon by it. 
     In a second embodiment, illustrated in FIGS. 4 and 5, the oil channel  92  is provided with a transverse channel  100  which extends radially to the cylinder axis  66  and ends with an opening  102  which is located in the cylinder surface  64  but is arranged so as to be offset forwards in relation to the entraining member surface  70  when seen in the direction of rotation  82  so that oil is supplied to the area  76  of the space  74  which runs ahead of the subsection  72  acted upon with a force during the movement of the second compressor member  18  on the orbital path  36 , this oil then moving in the direction of the subsection  72  and leading in the area of the subsection  72  between the entraining surface  60  and the entraining member surface  70  to a hydrodynamic oil film which lies between the entraining member surface  70  and the subsection  72  of the entraining surface  60  acted upon with a force. 
     As for the rest, the second embodiment is designed in the same way as the first embodiment and so the same parts are given the same reference numerals and in this respect reference can be made in full to the explanations concerning the first embodiment. 
     In a third embodiment of an inventive scroll compressor, the entraining unit  50 ″ is designed such that the entraining member  52  acts with the entraining member surface  70  on an intermediate ring  110  which bears the entraining surface  60 , the subsection  72  of which is acted upon with a force by the entraining member surface  70 . The intermediate ring  110  does, however, also have an outer cylinder surface  112  which is arranged coaxially to the entraining surface  60  and forms an entraining member surface  120  which, for its part, then acts on an entraining surface  130  designed as a cylinder surface in relation to the cylinder axis  62 , wherein the additional entraining member surface  120  acts only in the area of an additional subsection  122  on the additional entraining surface  130  which represents an inner surface of the entraining member receiving means  54 . 
     Thus, an additional space  124  is provided in addition to the space  74 , and both spaces  74  and  124  contribute to the radial degree of freedom of the entraining member receiving means  54  relative to the entraining member  52 . 
     This solution has the advantage that the widths W 1  and W 2  of the spaces  74  and  124  contributing to the radial degree of freedom in the direction of the connection line  86  are added together so that altogether the spaces  74  and  124  can each have individually a smaller width W 1  and W 2 , respectively, but altogether the movability of the second compressor member  18  with the second scroll rib  26  required for the radial degree of freedom results from the sum of the two widths W 1  and W 2  so that despite smaller widths of the individual spaces  74  and  124  altogether an adequately large radial movability can be achieved. 
     The small widths W 1  and W 2  of the spaces  74  and  124  also allow a good lubrication and an even better attenuation against oscillating movements of the second compressor member relative to the entraining member  52  since the possibility exists of maintaining a supply of oil in the spaces  74  and  124  which can, indeed, be displaced in order to carry out a movement in a radial direction, wherein, however, it acts in an attenuating manner in relation to higher frequency oscillating movements as a result of the displacement. 
     As for the rest, those parts of the third embodiment which are identical to those of the preceding embodiments are provided with the same reference numerals and so with respect to the further description thereof reference can be made in full to the explanations concerning the preceding embodiments.