Patent Publication Number: US-8992188-B2

Title: Revolution type compressor

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a revolution type compressor which is constructed by housing a compression mechanism for compressing a refrigerant, a drive shaft for driving the compression mechanism, and an electric motor for rotating the drive shaft in a hermetically sealed chamber, and fixedly providing a balance weight for balancing a rotating mass of the aforementioned compression mechanism at the aforementioned drive shaft. 
     As the conventional revolution type compressor, there are known the ones each constructed by housing a compression mechanism for compressing a refrigerant, a drive shaft for driving the compression mechanism, and an electric motor for revolving the drive shaft in a hermetically sealed chamber (hermetically sealed container), as described in JP-A-2001-218411, JP-A-2001-234863 and JP-A-2000-73977, and the aforementioned electric motor includes a stator fixed to the hermetically sealed container, and a rotor connected to a drive part. Further, a balance weight for balancing the rotating mass of the aforementioned compression mechanism is disposed at the aforementioned drive shaft, and the balance weight is constructed into a cylindrical shape by a weight part in a substantially semicircular column shape for balancing the rotating mass, and a substantially semi-cylindrical cover part provided at an opposite side in the radial direction from the weight part. It is known that the cylindrical balance weight prevents agitation of the refrigerant to suppress oil churn. 
     BRIEF SUMMARY OF THE INVENTION 
     A structure example of the compressor in the above described prior art is shown in  FIG. 2 . By forming the balance weight into the shape as in  FIG. 2 , churn of the refrigerant by the balance weight can be prevented and oil scattering reduction effect is obtained, as compared with the conventional structure illustrated in  FIG. 3(A)  of JP-A-2000-73977. However, as shown in  FIG. 2 , part of the oil supplied to a main bearing  18  accumulates in an inside  90   a  of a cylindrical balance weight  90 , the oil accumulating in the inside  90   a  of the balance weight revolves with the balance weight, and therefore, input of the compressor is increased. Further, oil overflows from the inside of the balance weight and scatters in the radial direction by the centrifugal force of the balance weight, and flows out to the outside of the compressor from a discharge pipe  102  without dropping into an oil sump  103  at the lower portion of the compressor. The oil flowing out to the outside of the compressor adheres to the inside of the heat exchanger constructed by the refrigeration cycle, and reduces the heat exchange efficiency to decrease performance of the refrigeration cycle. 
     Further, as described in JP-A-2001-234863, it is known that a rotor and a cylindrical balance weight are constructed to be an integrated piece, an oil discharge hole penetrating in the axial direction is provided inside the rotor so that oil does not accumulate inside the cylindrical balance weight. However, oil has to be discharged downward and perpendicularly to the direction of the centrifugal force by the rotor, and oil discharge performance is low. Further, in the one in the cited document 2, the rotor in which the permanent magnet is disposed, and the balance weight which is a magnetic substance are integrated, and therefore, there is the disadvantage that the magnetic flux of the rotor leaks to reduce the efficiency of the electric motor, and increases the input of the compressor. 
     An object of the present invention is to enhance the effect of reducing oil churn, and to reduce input power of a compressor in a revolution type compressor including a balance weight for balancing a rotating mass. 
     According to the invention for achieving the object, a revolution type compressor for compressing a refrigerant, comprises: a compressing mechanism for compressing the refrigerant, a drive shaft for driving the compressing mechanism, an electric motor for rotating the drive shaft, a hermetically sealed container containing the compressing mechanism, the drive shaft and the electric motor, and a balance weight arranged on the drive shaft to be balanced in rotating mass with the compressing mechanism, the electric motor including a stator fixed to the container and a rotor connected to the drive shaft, wherein the balance weight has a weight portion of semicircular column shape for balancing the balance weight and the compressing mechanism in rotating mass with each other, a cover portion of semi-cylindrical shape being opposite radially to the weight portion and including openings arranged at its lower and upper areas respectively, and a hollow space surrounded by the weight portion and the cover portion, and the balance weight and the rotor are distant from each other to form an axial clearance therebetween. 
     The compressor may further comprise a positioning member arranged in the axial clearance and prevented from extending to close the opening at the lower area of the cover portion. The positioning member may have a fluidal path communicating fluidly with the opening at the lower area of the cover portion. Further, the rotor may have another fluidal path to communicate fluidly with the fluidal path at an axial end surface of the rotor facing to the positioning member. 
     As another aspect of the invention, a revolution type compressor for compressing a refrigerant, comprises: a compressing mechanism for compressing the refrigerant, a drive shaft for driving the compressing mechanism, an electric motor for rotating the drive shaft, a hermetically sealed container containing the compressing mechanism, the drive shaft and the electric motor, and a balance weight arranged on the drive shaft to be balanced in rotating mass with the compressing mechanism, the electric motor including a stator fixed to the container and a rotor connected to the drive shaft, wherein the balance weight has a weight portion of semicircular column shape for balancing the balance weight and the compressing mechanism in rotating mass with each other, a cover portion of semi-cylindrical shape being opposite radially to the weight portion and including openings arranged at its lower and upper areas respectively, and a hollow space surrounded by the weight portion and the cover portion, and the compressor further comprises a positioning member arranged between the balance weight and the rotor, and prevented from extending to close the opening at the lower area of the cover portion. 
     As the other aspect of the inventions, a revolution type compressor for compressing a refrigerant, comprises: a compressing mechanism for compressing the refrigerant, a drive shaft for driving the compressing mechanism, an electric motor for rotating the drive shaft, a hermetically sealed container containing the compressing mechanism, the drive shaft and the electric motor, and a balance weight arranged on the drive shaft to be balanced in rotating mass with the compressing mechanism, the electric motor including a stator fixed to the container and a rotor connected to the drive shaft, wherein the balance weight has a weight portion of semicircular column shape for balancing the balance weight and the compressing mechanism in rotating mass with each other, a cover portion of semi-cylindrical shape being opposite radially to the weight portion and including openings arranged at its lower and upper areas respectively, a hollow space surrounded by the weight portion and the cover portion, and a protruding portion extending toward the rotor from the vicinity of the opening at the lower area and contacting the rotor. 
     The rotor may include permanent magnets. It is preferable for the rotor to include permanent magnets, while the positioning member is made of non-magnetic material. 
     When the rotor includes permanent magnets, it is preferable for the positioning member to have an outer peripheral diameter less than an inscribed circle diameter of the permanent magnets. 
     It is preferable that the rotor includes permanent magnets, and an outer peripheral diameter of the protruding portion is less than an inscribed circle diameter of the permanent magnets. 
     It is preferable that the balance weight is made of magnetic material such as iron or the like. 
     By constructing the balance weight as described above, in the one in which a clearance is provided in the axial direction of the balance weight and the rotor, the oil which drops to the inside of the balance weight can be discharged to the outer periphery of the upper portion of the rotor through the clearance. 
     More specifically, the oil which drops to the inside of the balance weight is discharged to the space in the upper portion of the rotor without accumulating inside the balance weight, is further discharged to the outer periphery of the rotor by the action of the centrifugal force of the rotor, and is returned to the oil sump provided at the lower portion of the compressor through the clearance provided between the inside of the hermetically sealed container and the stator. Thereby, input of the compressor reduces, and the compressor with less power consumption can be obtained. Further, the oil which flows outside the compressor can be decreased, and the performance of the refrigeration cycle can be enhanced by reducing oil churn. 
     Further, in the case of use of the electric motor of the structure in which a permanent magnet is placed inside the rotor, leakage of the magnetic fluxes of the rotor can be reduced. Therefore, there is provided the effect of securing the electric motor efficiency and preventing increase in input of the compressor. 
     Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a vertical sectional view showing example 1 of a revolution type compressor of the present invention; 
         FIG. 2  is a vertical sectional view of a conventional revolution type compressor; 
         FIG. 3A  is a vertical sectional view showing a balance weight shown in  FIG. 1  by enlarging it and  FIG. 3B  is a plane view of the same; 
         FIG. 4  is a sectional view showing arrangement relationship of the balance weight and a rotor which are fixed to a drive shaft in the example shown in  FIG. 1 ; 
         FIG. 5  is a view showing a modified example of  FIG. 4 , and is a view corresponding to  FIG. 4 ; 
         FIGS. 6A and 6B  are views showing a positioning member shown in  FIG. 5  by enlarging it,  FIG. 6A  is a vertical sectional view, and  FIG. 6B  is a plane view; 
         FIG. 7  is a view showing another modified example of  FIG. 4 , and is a view corresponding to  FIG. 4 ; 
         FIGS. 8A and 8B  are enlarged views of the positioning member shown in  FIG. 7 ,  FIG. 8A  is a vertical sectional view, and  FIG. 8B  is a plane view; 
         FIG. 9  is a view showing still another modified example of  FIG. 4 , and is a view corresponding to  FIG. 4 ; 
         FIGS. 10A and 10B  are enlarged views of the positioning member shown in  FIG. 9 ,  FIG. 10A  is a vertical sectional view, and  FIG. 10B  is a plane view; 
         FIGS. 11A and 11B  are enlarged views of a rotor shown in  FIG. 9 ,  FIG. 11A  is a plane view, and  FIG. 11B  is a vertical sectional view; 
         FIG. 12  is a view showing still another modified example of  FIG. 4 , and is a view corresponding to  FIG. 4 ; 
         FIGS. 13A and 13B  are views showing the details of a balance weight shown in  FIG. 12 ,  FIG. 13A  is a vertical sectional view thereof, and  FIG. 13B  is a plane view thereof; 
         FIG. 14  is a view showing yet another modified example of  FIG. 4 , and is a view corresponding to  FIG. 4 ; 
         FIGS. 15A and 15B  are views showing the details of the balance weight shown in  FIG. 14 , FIG.  15 A is a vertical sectional view thereof, and  FIG. 15B  is a plane view thereof; and 
         FIGS. 16A and 16B  show a structure example of a rotor of a permanent magnet synchronous electric motor with a permanent magnet internally placed,  FIG. 16A  is a plane view thereof, and  FIG. 16B  is a vertical sectional view thereof. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an example of the present invention will be described based on the drawings. 
     EXAMPLE 1 
       FIG. 1  shows example 1 of a revolution type compressor of the present invention, and is a general structural view of the case of being applied to a scroll compressor. A scroll compressor  1  is constructed by housing a compression mechanism  2 , a drive shaft  3  and an electric motor  4  in a hermetically sealed container  100 , and is of a vertical structure in which the compression mechanism  2  and the electric motor  4  are vertically arranged. The compression mechanism  2  includes an orbiting scroll  5 , a fixed scroll  6 , a frame  7 , a drive shaft  3 , a bearing  10  for orbiting scroll and an orbiting mechanism  9 . Further, the compression mechanism  2  forms a compressor area  30  by combining the fixed scroll  6  and the orbiting scroll  5 , and the aforementioned orbiting scroll  5  includes a spiral wrap  11  and an end plate  12 . At the rear surface side of the end plate  12  of the orbiting scroll  5 , the orbiting mechanism  9  which is constructed by an Oldham ring or the like is provided, and the bearing  10  for orbiting scroll in which a crankshaft  13  of the drive shaft  3  is inserted is provided. The fixed scroll  6  includes a spiral wrap  14 , an end plate  15 , a suction port  16  and a discharge port  17 , and is fixed to the frame  7  via a bolt. By the above described construction, the aforementioned orbiting scroll  5  is sandwiched between the fixed scroll  6  and the frame  7  to be capable of orbiting movement. 
     A suction pipe  101  provided at the hermetically sealed container  100  is connected to the suction port  16  of the fixed scroll  6 . Further, a discharge pipe  102  is provided at the hermetically sealed container  100  so as to communicate with a space between the frame  7  and the electric motor  4 . The frame  7  has its outer peripheral portion fixed to the hermetically sealed container  100 , and a main bearing  18  is provided in its central portion between the electric motor  4  and the orbiting scroll  5 . The drive shaft  3  has the crankshaft  13  at the upper portion of the main bearing, and drives the orbiting scroll  5  by inserting and engaging the crankshaft  13  in the bearing  10  for orbiting scroll provided at the rear surface of the orbiting scroll  5 . 
     The electric motor  4  constructs revolution drive means for driving the compression mechanism  2  via the drive shaft  3 , and has a stator  19  and a rotor  20  as basic elements. The outer peripheral surface of the stator  19  is fixed to be substantially in close contact with the inner peripheral surface of the hermetically sealed container  100 . When the drive shaft  3  is rotated by the rotation of the electric motor  4 , the orbiting scroll  5  performs orbiting movement with respect to the fixed scroll  6  while keeping the posture by the function of the orbiting mechanism  9 . In order to cancel the unbalanced force which occurs due to its orbiting movement, a balance weight  50  which is fixed to the drive shaft between the rotor  20  and the orbiting scroll  5 , and a rotor balance weight  21  which is fixed to the lower portion of the rotor  20 , are provided. 
     In the compressor area  30  which is formed by meshing of the fixed scroll  6  and the orbiting scroll  5 , a compression operation with its volumetric capacity decreasing is performed by orbiting movement of the orbiting scroll  5 . In the compression operation, an operating fluid is sucked into the compressor area  30  from the suction port  16  with the orbiting movement of the orbiting scroll  5 , the sucked operating fluid is discharged to the discharge space in the hermetically sealed container  100  from the discharge port  17  of the fixed scroll  6  through the compression stroke, thereafter, flows into the space where the electric motor  4  is arranged, and is further discharged outside the hermetically sealed container  100  through the discharge pipe  102 . Thereby, the space in the hermetically sealed container  100  is kept at a discharge pressure. 
       FIG. 3A  is a vertical sectional view and  FIG. 3B  is a plane view each showing the balance weight  50  shown in  FIG. 1  by enlarging it. The balance weight  50  is constructed by a weight portion  50   a , a cover portion  50   b  and a boss portion  50   c . The upper and lower end surfaces of the balance weight are opened to communicate with an upper space and a lower space of the balance weight. Therefore, the balance weight is of the structure in which oil does not accumulate inside the balance weight. 
     In the case of adoption of a cylindrical balance weight using a non-magnetic substance other than iron, for example, zinc, as the material of the balance weight, the density is smaller by about 10 to 15% as compared with iron and the like, and therefore, the volume of the balance weight needs to be larger by 10 to 15% as compared with the balance weight of iron or the like, and reduction in size and weight of the compressor becomes difficult. In the case of use of copper with a large density as the material of the balance weight, reduction in size and weight of the compressor is possible, but the material unit price becomes high as compared with iron, and the cost of the compressor increases. 
     Further, in the case of an ordinary compressor having a large number of components using iron, if the balance weight is constructed by a material other than iron, troubles due to difference in the material characteristic easily occur. For example, when the thermal expansion coefficient differs significantly, the deformation amount differs before and during operation, and therefore, the fastening margins and clearances of the components before and during operation differ, which becomes the constraint in design. In order to attain reduction in size, weight and cost of the compressor in such a background as well as to minimize design restrictions, adoption of the balance weight of iron is preferable. 
       FIG. 4  is a sectional view showing the arrangement relationship of the balance weight  50  and the rotor  20  which are fixed to the drive shaft  3 . An inside diameter  50   d  of the boss portion  50   c  of the balance weight  50  is made to be smaller than a hold part outside diameter  3   b  of a balance weight hold part  3   a  of the drive shaft  3 , and the boss portion  50   c  of the balance weight  50  is fastened to the balance weight hold part  3   a  of the drive shaft  3  by press fitting or shrink fitting. A stepped portion  3   e  is provided at the drive shaft  3 , and the balance weight  50  is fixed to the drive shaft  3  in the state in close contact with the stepped portion. 
     An inside diameter  20   a  of the rotor  20  is made to be smaller than a hold part outside diameter  3   d  of a rotor hold part  3   c  of the drive shaft  3 , and the rotor  20  is fastened to the drive shaft  3  by press fitting or shrink fitting. A stepped portion  3   f  is formed at the drive shaft  3 , and the rotor  20  is fixed to the drive shaft  3  in the state in close contact with the stepped portion  3   f . The stepped portion  3   f  is provided at the side of the rotor  20  from the lower end surface of the boss portion  50   c  of the balance weight  50 , and the rotor  20  is positioned by the stepped portion  3   f , whereby a clearance can be formed between the rotor  20  and the balance weight  50 . 
     With the above described structure, by arranging the rotor and the balance weight, the oil which drops inside the balance weight can be allowed to flow out to the lower portion of the balance weight without accumulating inside the balance weight. 
       FIG. 5  is a view showing a modified example of  FIG. 4 , and is a view corresponding to  FIG. 4 . The structure of the balance weight itself is the same as that shown in  FIGS. 3 and 4 . Fastening of the balance weight  50  and the rotor  20  to the drive shaft  3  is performed by fastening the balance weight  50  and the rotor  20  to the drive shaft  3  by press fitting or shrink fitting as in the case of  FIG. 4 . In this example, in order to positioning the rotor in the axial direction, a positioning member  51  is used. More specifically, the rotor is fastened to the drive shaft by press fitting or shrink fitting so that the positioning member  51  is sandwiched with the balance weight and the rotor. In this case, the balance weight hold part  3   a  and the rotor hold part  3   c  of the drive shaft  3  can have the same diameters, and work of the drive shaft becomes easy. 
       FIGS. 6A and 6B  are views showing the positioning member  51  shown in  FIG. 5  by enlarging it,  FIG. 6A  is a vertical sectional view, and  FIG. 6B  is a plane view. An inside diameter  51   a  of the positioning member  51  is a little larger than the hold part outside diameter  3   d  of the drive shaft  3 , and an outside diameter  51   b  of the positioning member  51  is set to be such a dimension as not to close the opening of the lower portion of the cover portion  50   b  of the balance weight  50 . 
     By using the positioning member in such a shape, the oil which drops inside the balance weight can be caused to flow out to the outer peripheral side of the upper portion of the rotor through the passage formed between the rotor and the lower end of the balance weight by the positioning member  51 . 
       FIG. 7  is a view showing still another modified example of  FIG. 4 , and is a view corresponding to  FIG. 4 . In this modified example, the shape of the balance weight is the same as that shown in  FIGS. 3A and 3B  and  4 . Further, fastening of the balance weight  50  and the rotor  20  to the drive shaft  3  is the same as that in the example of  FIG. 4 . Further, as in the example of  FIG. 5 , a positioning member  52  is provided, and fastening of it to the drive shaft is similar to the example of  FIG. 5 . The point in which the modified example differs from the example of  FIG. 5  is the shape of the positioning member  52 . 
       FIGS. 8A and 8B  are enlarged views of the positioning member  52  shown in  FIG. 7 ,  FIG. 8A  is a vertical sectional view, and  FIG. 8B  is a plane view. As in the example shown in  FIG. 6 , an inside diameter  52   a  of the positioning member  52  is constructed to be a little larger than the hold part outside diameter  3   d  of the drive shaft  3 , but in this example, an outside diameter  52   b  of the positioning member  52  is constructed to be substantially the same size as the outside diameter  20   b  of the rotor  20 . Further, a channel (passage of the positing member)  52   c  in the radial direction is formed in the outer peripheral side of the positioning member  52 , and the passage  52   c  communicates with the opening at the lower end of the cover portion  50   b  of the balance weight  50 , and the outer peripheral side end of the passage  52   c  of the positioning member opens to the outer peripheral side of the positioning member  52 . 
     By such a construction, the oil which drops inside the balance weight is caused to flow out to the outer peripheral side of the upper portion of the rotor through the passage formed by the aforementioned channel. 
       FIG. 9  is a view showing still another modified example of  FIG. 4 , and is a view corresponding to  FIG. 4 . In this modified example, the shape of the balance weight is the same as that shown in  FIGS. 3A and 3B , and  4 , and fastening of the balance weight  50  and the rotor  20  to the drive shaft  3  is the same as in the example of  FIG. 4 . Further, as in the examples of  FIGS. 5 and 7 , a positioning member  53  is provided, and fastening of the positioning member  53  to the drive shaft  3  is the same as in the example of  FIG. 5 . The point in which the modified example differs from the example of  FIG. 5  is the shape of the positioning member  53 . 
       FIGS. 10A and 10B  are enlarged views of the positioning member  53  shown in  FIG. 9 ,  FIG. 10A  is a vertical sectional view, and  FIG. 10B  is a plane view. Further,  FIGS. 11A and 11B  are enlarged views of the rotor  20  shown in  FIG. 9 ,  FIG. 11A  is a plane view, and  FIG. 11B  is a vertical sectional view. 
     An inside diameter  53   a  of the positioning member  53  is a little larger than the hold part outside diameter  3   b  of the drive shaft  3 , and an outside diameter  53   b  of the positioning member  53  is equivalent to the outside diameter  20   b  of the rotor  20 . A hole (passage or space of the positioning member)  53   c  in the circumferential direction is formed in the positioning member  53  to communicate with the opening at the lower end of the cover portion  50   b  of the balance weight  50 . Reference numeral and character  20   a  denotes an inside diameter of the rotor  20 . 
     Further, as shown in  FIGS. 11A and 11B , a disk-shaped member  20   f  is provided at an upper end surface of the rotor  20 , and a channel  20   c  in the radial direction which communicates with the passage  53   c  of the positioning member and opens to the outer peripheral side is formed at the outer peripheral side of the disk-shaped member  20   f . By adopting such a construction, the oil which drops inside the balance weight is caused to flow out to the outer peripheral side of the upper portion of the rotor from the opening at the lower end of the cover portion  50   b  of the balance weight  50  through the passage  53   c  of the positioning member and the channel  20   c  of the disk-shaped member provided at the upper end surface of the rotor. 
       FIG. 12  is a view showing still another modified example of  FIG. 4 , and is a view corresponding to  FIG. 4 . Fastening of the rotor  20  to the drive shaft  3  is the same as in the example of  FIG. 4 . Further, in this example, a balance weight  54  and the positioning member  52  are fixed to the rotor  20  by using a caulked pin  104  which penetrates through the rotor  20 , the positioning member  52  and the balance weight  54  and by caulking the end portions of the caulked pin  104 . The structure of the aforementioned positioning member  52  includes a passage  52   c  in the radial direction of the positioning member, and the opening at the lower portion of the aforementioned cover portion of the balance weight is not closed, as in the positioning member  52  shown in  FIGS. 7 , and  8 A and  8 B. 
       FIGS. 13A and 13B  are views showing the details of the balance weight  54  shown in  FIG. 12 ,  FIG. 13A  is a vertical sectional view of it, and  FIG. 13B  is a plane view. In this example, the balance weight is constructed by a weight portion  54   a  in a substantially semicircular column shape for balancing the rotating mass, and a cover portion  54   b  in a substantially semi-cylindrical shape having an opening in the vicinity of upper and lower portions, at the opposite side in the radial direction from the weight portion, and the inside of the balance weight is a hollow space surrounded by the aforementioned weight portion and the cover portion. Reference numeral and character  54   c  denotes a through-hole for a caulked pin  104  to penetrate through. 
       FIG. 14  is a view showing still another modified example of  FIG. 4 , and is a view corresponding to  FIG. 4 . Fastening of a balance weight  55  and the rotor  20  to the drive shaft  3  is the same as in the example of  FIG. 4 . 
       FIGS. 15A and 15B  are views showing the details of the balance weight  55  shown in  FIG. 14 , FIG.  15 A is a vertical sectional view of it, and  FIG. 15B  is a plane view. In this example, the balance weight is constructed by a weight portion  55   a  in a substantially semicircular column shape for balancing the rotating mass, and a cover portion  55   b  in a substantially semi-cylindrical shape having an opening in the vicinity of the upper and lower sides, at the opposite side in the radial direction from the weight portion, and the inside of the balance weight is a hollow space surrounded by the aforementioned weight portion and the cover portion. 
     In this example, a projecting portion  55   e  which projects to the rotor  20  side from the lower end portion of a boss portion  55   c  of the balance weight is provided integrally with the boss portion without providing the positioning member as shown in  FIG. 5 , and the projecting portion  55   e  is brought into contact with the upper end portion of the aforementioned rotor  20 , whereby the balance weight  55  is positioned. 
     As the electric motor described in the above described example, a permanent magnet synchronous motor (DC brushless motor) in which a permanent magnet is provided at the rotor  20 , a self excitation synchronous motor which includes a cage conductor and a permanent magnet in the rotor and is capable of self excitation without using an inverter and the like can be used in addition to an induction motor having the rotor  20  having a cage conductor. 
       FIGS. 16A and 16B  show a structure example of the rotor  20  of the permanent magnet synchronous motor internally provided with a permanent magnet  20   d ,  FIG. 16A  is a plane view of it, and  FIG. 16B  is a vertical sectional view. The permanent magnets  20   d  are placed at the four spots in the circumferential direction as shown in  FIG. 16A . Reference numeral and character  20   e  denotes the diameter of the circle contacting the inner sides of the four permanent magnets, that is, the diameter of arrangement of the permanent magnets as an inscribed circle diameter of the permanent magnets. The projecting portion  55   e  of the boss portion of the balance weight  55  is constructed to be at the inner side from the diameter  20   e  of arrangement of the aforementioned permanent magnets, whereby even when the balance weight is constructed by iron, the influence given to the magnetic fluxes generated by the permanent magnets  20   d  can be made small. 
     By constructing the balance weight portion as described in the aforementioned example, a clearance for causing oil to flow out can be provided between the balance weight and the rotor, and through this clearance, the oil which drops to the inside of the balance weight can be discharged to the outer periphery of the upper portion of the rotor. Thereby, input of the compressor can be reduced, the compressor with less power consumption can be obtained, and the oil flowing outside the compressor can be decreased. Therefore, the performance of the refrigeration cycle can be enhanced by reduction in oil churn. 
     Further, even when the electric motor of the structure in which the permanent magnets are placed inside the rotor is used, leakage of the magnetic fluxes of the rotor can be reduced by adopting the constructions shown in  FIGS. 4 ,  5  and  14 , or by using the material other than iron (non-magnetic substance) as the positioning member. Therefore, there is provided the effect of securing the electric motor efficiency and being capable of preventing increase in input of the compressor. 
     It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.