Patent Publication Number: US-2020284257-A1

Title: Scroll compressor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2019-0026741, filed on Mar. 8, 2019, which is hereby incorporated by reference as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a compressor having a structure for compensating for eccentricity of a rotary shaft caused by a driving load. 
     Discussion of the Related Art 
     Generally, a compressor is applied to a vapor compression type refrigeration cycle (hereinafter referred to simply as a refrigeration cycle) such as a refrigerator or an air conditioner. The compressor compresses the refrigerant to provide work necessary for heat exchange in the refrigeration cycle. Compressors can be divided into reciprocating compressors, rotary compressors, and scroll compressors according to how the refrigerant is compressed. 
     The reciprocating compressor is a system in which the volume of the compression space is varied while the piston reciprocates in the cylinder. The rotary compressor compresses the refrigerant while the rolling piston pivotally moves using the rotating force of the drive unit. 
     The scroll compressor is a compressor in which an orbiting scroll is pivotably engaged with a fixed scroll fixed in the inner space of a hermetically sealed container to form a compression chamber between a fixed lap of the fixed scroll and an orbiting lap of the orbiting scroll. When the orbiting scroll rotates, the refrigerant is introduced, compressed and discharged as the volume of the compression chamber varies. 
     The scroll compressor is widely employed in an air conditioner or the like to compress a refrigerant because it can obtain a relatively high compression ratio as compared with other types of compressors and can obtain a stable torque as the intake, compression and discharge operations of the refrigerant are smoothly connected to each other. 
     Scroll compressors may be divided into an upper compression compressor or a lower compression compressor depending on the positions of the drive motor and the compression unit. In the upper compression compressor, the compression unit is positioned over the drive motor. In the lower compression compressor, the compression unit is positioned under the drive motor. 
     Here, in the case of the lower compression scroll compressor, a discharge cover is hermetically coupled to the lower surface of the fixed scroll to prevent the refrigerant discharged from the compression chamber to the inner space of the casing from mixing with the oil contained in an oil reservoir space. 
     Referring to U.S. Patent Application Publication No. 2017/0067466, a conventional scroll compressor includes a case defining an outer appearance and having a discharge portion through which a refrigerant is discharged, a compression unit fixed to the case and configured to compress the refrigerant, and a drive unit is fixed to the case and configured to drive the compression unit, wherein the compression unit and the drive unit are connected by a rotary shaft rotatably coupled to the drive unit. 
     The compression unit includes a fixed scroll fixed to the case and having a fixed lap, and an orbiting scroll including an orbiting lap engaging with the fixed lap and driven by the rotary shaft. In the conventional scroll compressor, the rotary shaft is eccentrically disposed, and the orbiting scroll is fixed to the eccentric rotary shaft and rotated. Thereby, the orbiting scroll revolves (orbits) around the fixed scroll to compress the refrigerant. 
       FIGS. 1A and 1B  are sectional views showing the structure of a rotary shaft and a bearing of a conventional scroll compressor.  FIG. 1A  is a view showing the shape of the bearing and the rotary shaft  226 , and  FIG. 1B  is a sectional view of  FIG. 1A . 
     As shown in  FIG. 1A , the rotary shaft and the bearing arranged around and rotatably coupled to the rotary shaft are engaged with the main frame and the fixed scroll, and thus the position thereof is fixed when the rotary shaft rotates. That is, the main frame and the fixed scroll are fixed so as not to rotate, and the bearing is interposed such that the rotary shaft can rotate with minimized friction. 
     As shown in  FIG. 1B , the bearing may be designed to have an inner diameter slightly larger than the diameter of the rotary shaft such that the bearing and the rotary shaft are not in contact with each other but spaced apart from each other by a predetermined distance. The scroll compressor includes an eccentric portion of the orbiting scroll for varying the volume of the compression space. The eccentric portion should have a sufficient size to sufficiently induce a volume change during rotation of the orbiting scroll. However, when the scroll compressor rotates occurs, a portion of the rotary shaft where the orbiting scroll is positioned tends to bend. 
       FIGS. 2A and 2B  are views showing the rotary shaft and the bearing during rotation of the rotary shaft. As the orbiting scroll portion is eccentric, the rotary shaft is bent when it rotates as shown in  FIG. 3 . 
     If the orbiting scroll comes into contact with the bearing and friction occurs, an oil film may not be formed uniformly, and the rotation of the orbiting scroll may become unstable. In addition, abrasion caused by friction and power load may be increased, resulting in durability and performance deterioration of the scroll compressor. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a scroll compressor that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a scroll compressor capable of addressing performance deterioration of a bearing resulting from eccentricity of a rotary shaft caused by a driving load. 
     The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention which are not mentioned may be understood upon examination of the following description and more clearly understood upon examination of the embodiments of the present invention. The objects and other advantages of the invention may be realized and attained by means particularly pointed out in the appended claims. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a scroll compressor includes a casing, a drive motor arranged in an inner space of the casing, a rotary shaft coupled to the drive motor to rotate, a main frame arranged under the drive motor, a fixed scroll arranged under the main frame, an orbiting scroll engaging with the orbiting scroll to make an orbiting motion, the rotary shaft being inserted into and eccentrically coupled to the orbiting scroll, a first bearing positioned between the main frame and the rotary shaft, and a second bearing positioned between the fixed scroll and the rotary shaft, wherein a gap between the first and second bearings and the rotary shaft varies with a vertical position. 
     The rotary shaft may be disposed such that a center of mass thereof is displaced from a center of the scroll compressor to one side. 
     A portion of the rotary shaft between the first bearing and the second bearing may be asymmetric. 
     A gap between a lower portion of the first bearing and the rotary shaft may be wider than a gap between an upper portion of the first bearing and the rotary shaft. 
     A gap between an upper portion of the second bearing and the rotary shaft may be wider than a gap between a lower portion of the second bearing and the rotary shaft. 
     At least one of the first bearing and the second bearing may include a first ring having a first diameter and a second ring having a second diameter greater than the first diameter, wherein the first ring and the second ring may be arranged side by side in a vertical direction. 
     At least one of the first bearing and the second bearing may include an inclined surface on an inner side surface thereof, wherein a distance from the inclined surface to the rotary shaft may gradually change. 
     A main journal of the rotary shaft surrounded by the first bearing and a sub-journal of the rotary shaft surrounded by the second bearing may have a diameter varying with a vertical position. 
     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
         FIGS. 1A to 2B  are views showing a rotary shaft and a bearing of a conventional scroll compressor; 
         FIG. 3  is a sectional view illustrating a scroll compressor according to an embodiment of the present invention; and 
         FIGS. 4A to 6B  are views showing the rotary shaft and bearing of the scroll compressor of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     Hereinafter, a scroll compressor according to an embodiment of the present invention will be described with reference to  FIG. 3 . 
       FIG. 3  is a sectional view illustrating a scroll compressor according to an embodiment of the present invention. 
     A scroll compressor  1  according to the embodiment of the present invention may include a casing  210  having an inner space, a drive motor  220  provided in an upper portion of the inner space, a compression unit  200  disposed under the drive motor  220 , and a rotary shaft  226  configured to transmit the driving force of the drive motor  220  to the compression unit  200 . 
     Here, the inner space of the casing  210  includes a first space V 1 , which is at an upper side of the drive motor  220 , and a second space V 2 , which is a space between the drive motor  220  and the compression unit  200 . The space under the fixed scroll  250  may be divided into a third space V 3  (closed space) defined by a discharge cover  270  hermetically coupled to a lower portion of the fixed scroll  250 , and a fourth space V 4  (oil reservoir space), which is under the compression unit  200 . 
     The casing  210  may have, for example, a cylindrical shape. Thus, the casing  210  may include a cylindrical shell  211 . An upper shell  212  may be provided to an upper portion of the cylindrical shell  211  and a lower shell  214  may be provided to a lower portion of the cylindrical shell  211 . The upper and lower shells  212  and  214  may be joined to the cylindrical shell  211  by, for example, welding to define an inner space. 
     Here, the upper shell  212  may be provided with a refrigerant discharge pipe  216 . The refrigerant discharge pipe  216  is a passage through which a compressed refrigerant discharged from the compression unit  200  to the second space V 2  and the first space V 1  is discharged to the outside. For reference, an oil separator (not shown) for separating the oil mixed in the discharged refrigerant may be connected to the refrigerant discharge pipe  216 . 
     The lower shell  214  may define an oil reservoir space V 4  capable of storing oil. The oil reservoir space V 4  may function as an oil chamber for supplying oil to the compression unit  200  to allow the compressor  1  to smoothly operate. 
     Further, a refrigerant suction pipe  218  serving as a passage through which the refrigerant to be compressed is introduced may be provided on the side surface of the cylindrical shell  211 . The refrigerant suction pipe  218  may extend to a compression chamber Si along the side of the fixed scroll  250  in a penetrating manner. 
     The drive motor  220  may be arranged in the upper operation of the casing  210 . Specifically, the drive motor  220  may include a stator  222  and a rotor  224 . 
     The stator  222  may be cylindrical, for example, and may be fixed to the casing  210 . The stator  222  has a plurality of slots (not shown) formed on the inner circumferential surface thereof in a circumferential direction such that a coil  222   a  is wound. In addition, the outer circumferential surface of the stator  222  may be cut into a D-cut shape to form a refrigerant channel groove  212   a  to allow the refrigerant or oil discharged from the compression unit  200  to pass therethrough. 
     The rotor  224  may be coupled to the inside of the stator  222  and may generate rotational power. The rotary shaft  226  may be precisely fitted into the center of the rotor  224  such that the rotary shaft  226  can rotate together with the rotor  224 . The rotational power generated by the rotor  224  is transmitted to the compression unit  200  through the rotary shaft  226 . 
     The compression unit  200 , is arranged under the drive motor  220 , may include a fixed scroll  250  coupled to the casing  210 , an orbiting scroll  240  coupled with the rotary shaft  226  and engaged with the fixed scroll  250  to form a compression chamber, and a main frame  230  configured to accommodate the orbiting scroll  240  and seated on the fixed scroll  250  to form an outer appearance of the compression unit  200 . The compression unit  200  may further include an Oldham ring  150  arranged between the main frame  230  and the orbiting scroll  240  to prevent the orbiting scroll  240  from rotating on the axis thereof 
     The main frame  230  may be provided under the drive motor  220  and form the top of the compression unit  200 . The main frame  230  may include a frame head plate  232  (hereinafter referred to as a first head plate) having a substantially circular shape, and a frame bearing  232  (hereinafter referred to as a first bearing) disposed at the center of the first head plate  232  and penetrated by the rotary shaft  226 , and a frame sidewall portion  231  (hereinafter referred to as a first sidewall portion) protruding downward from an outer circumferential portion of the first head plate  232 . 
     The outer circumferential portion of the first sidewall portion  231  may be in contact with the inner circumferential surface of the cylindrical shell  211 , and the lower end of the first sidewall portion  231  may be in contact with the upper end of a fixed scroll sidewall portion  255 , which will be described later. 
     The first sidewall portion  231  may be provided with a frame discharge hole  231   a  (hereinafter referred to as a first discharge hole) which penetrates the first sidewall portion  231  in the axial direction and forms a refrigerant passage. The inlet of the first discharge hole  231   a  may be connected to the outlet of a fixed scroll discharge hole  256   b,  which will be described later, and the outlet of the first discharge hole  231   a  may be connected to the second space V 2 . 
     The first bearing  232   a  may protrude from the upper surface of the first head plate  232  toward the drive motor  220 . In addition, the first bearing  232   a  may be provided with a first rotation portion through which a main journal  226   c  of the rotary shaft  226 , which will be described later, is arranged so as to be supported. 
     That is, the first bearing  232   a,  through which the main journal  226   c  of the rotary shaft  226  is rotatably inserted and supported, may be formed at the center of the main frame  230  in the axial direction. 
     An oil pocket  232   b  for collecting oil discharged from a gap between the first bearing  232   a  and the rotary shaft  226  may be formed in the upper surface of the first head plate  232 . 
     Specifically, the oil pocket  232   b  may be engraved on the upper surface of the first head plate  232  and be formed in an annular shape along the outer circumferential surface of the first bearing  232   a.    
     A back pressure chamber S 2  may be formed on the bottom surface (i.e., the lower surface) of the main frame  230  to define a space together with the fixed scroll  250  and the orbiting scroll  240  such that t the orbiting scroll  240  is supported by the pressure in the space. 
     For reference, the back pressure chamber S 2  may be an intermediate pressure area (i.e., an intermediate pressure chamber) and an oil supply passage  226   a  provided in the rotary shaft  226  may be at a higher pressure than the back pressure chamber S 2 . Further, the space enclosed by the rotary shaft  226 , the main frame  230 , and the orbiting scroll  240  may be a high-pressure area. 
     A back pressure seal  280  may be provided between the main frame  230  and the orbiting scroll  240  to distinguish the high pressure area from the intermediate pressure area S 2 . The back pressure seal  280  may serve as, for example, a sealing member. 
     In addition, the main frame  230  may be coupled with the fixed scroll  250  to define a space in which the orbiting scroll  240  can be pivotably arranged. That is, this structure may be configured to surround the rotary shaft  226  such that rotational power can be transmitted to the compression unit  200  via the rotary shaft  226 . 
     The fixed scroll  250 , which forms the first scroll, may be coupled to the bottom surface of the main frame  230 . 
     Specifically, the fixed scroll  250  may be arranged under the main frame  230 . 
     The fixed scroll  250  may include a fixed scroll head plate (second head plate)  254  having a substantially circular shape, a fixed scroll sidewall portion  254  protruding upward from the outer circumferential portion of the second head plate  254 , a fixed lap  251  protruding from the upper surface of the second head plate  254  and meshing (i.e., engaging) with an orbiting lap  241  of the orbiting scroll  240 , which will be described later, to form the compression chamber S 1 , and a fixed scroll bearing accommodation portion  252  (hereinafter referred to as a second bearing accommodation portion) formed at the center of the back surface (i.e., lower surface) of the second head plate  254  and penetrated by the rotary shaft  226 . 
     The second head plate  254  may be provided with a discharge port  253  for guiding the compressed refrigerant from the compression chamber S 1  to the inner space of the discharge cover  270 . Further, the position of the discharge port  253  may be set in consideration of a required discharge pressure or the like. 
     Here, the discharge port  253  is arranged to face the lower shell  214 . Accordingly, the discharge cover  270  for accommodating the discharged refrigerant and guiding the refrigerant to a fixed scroll discharge hole  256   b,  which will be described later, so as not to be mixed with oil may be coupled to the bottom surface (i.e., lower surface) of the fixed scroll  250 . 
     The discharge cover  270  may be hermetically coupled to the bottom surface of the fixed scroll  250  to separate the refrigerant discharge passage from the oil reservoir space V 4 . The discharge cover  270  may be provided with a through hole (not shown) through which an oil feeder  271 , which is coupled to a sub-journal  226   g  of the rotary shaft  226  and submerged in the oil reservoir space V 4  of the casing  210 , is arranged. 
     For reference, the discharge cover  270  is also referred to as a muffler, and a detailed description thereof will be given later. 
     The outer circumferential portion of the second sidewall portion  255  may be in contact with the inner circumferential surface of the cylindrical shell  211  and the upper end portion of the second sidewall portion  255  may be in contact with the lower end portion of the first sidewall portion  231 . 
     The second sidewall portion  255  may be provided with a fixed scroll discharge hole  256   b  (hereinafter referred to as a second discharge hole) penetrating the second sidewall portion  255  in the axial direction to form a refrigerant passage together with the first discharge hole  231   a.    
     The second discharge hole  256   b  may be formed so as to correspond to the first discharge hole  231   a.  The inlet of the second discharge hole  256   b  may be connected to the inner space of the discharge cover  270  and the outlet of the second discharge hole  256   b  may be connected to the inlet of the first discharge hole  231   a.    
     Here, the second discharge hole  256   b  and the first discharge hole  231   a  may be formed to connect the third space V 3  and the second space V 2  such that the refrigerant discharged from the compression chamber S 1  into the inner space of the discharge cover  270  is guided to the second space V 2 . 
     The second sidewall  255  may be provided with a refrigerant suction pipe  218  connected to the suction side of the compression chamber S 1 . In addition, the refrigerant suction pipe  218  may be arranged spaced apart from the second discharge hole  256   b.    
     The second bearing  252  may protrude from the lower surface of the second head plate  254  toward the oil reservoir space V 4 . 
     A second rotation portion may be provided in the second bearing  252  such that a sub journal  226   g  of the rotary shaft  226 , which will be described later, is inserted into and supported by the second rotation portion. 
     In addition, the lower end portion of the second bearing  252  may be bent toward the center of the shaft to support the lower end of the sub-journal  226   g  of the rotary shaft  226  to form a thrust bearing surface. 
     The orbiting scroll  240 , which is formed as the second scroll, may be arranged between the main frame  230  and the fixed scroll  250 . 
     Specifically, the orbiting scroll  240  may be coupled to the rotary shaft  226  to form a pair of two compression chambers S 1  between the fixed scroll  250  and the orbiting scroll  240  while making an orbiting motion. 
     The orbiting scroll  240  may include an orbiting scroll head plate  245  (hereinafter referred to as a third head plate) having a substantially circular shape, an orbiting lap  254  protruding from the lower surface of the third head plate  245  and engaged with the fixed lap  251 , and a rotary shaft coupling portion  242  provided at the center of the third head plate  245  and rotatably coupled to an eccentric portion  226   f  of the rotary shaft  226 , which will be described later. 
     In the case of the orbiting scroll  240 , the outer circumferential portion of the third head plate  245  may be located at the upper end portion of the second sidewall portion  255  and the lower end portion of the orbiting lap  241  may be in close contact with the upper surface of the second head plate  254  so as to be supported by the fixed scroll  250 . 
     The outer circumferential portion of the rotary shaft coupling portion  242  is connected to the orbiting lap  241  to form the compression chamber Si together with the fixed lap  251  during the compression operation. 
     For reference, the fixed lap  251  and the orbiting lap  241  may be formed in an involute shape, or may be formed in various other shapes. 
     Here, the involute shape refers to a curve corresponding to a trajectory drawn by an end of a thread when the thread wound around a base circle having an arbitrary radius is released. 
     The eccentric portion  226   f  of the rotary shaft  226  may be inserted into the rotary shaft coupling portion  242 . The eccentric portion  226   f  inserted into the rotary shaft coupling portion  242  may overlap the orbiting lap  241  or the fixed lap  251  in the radial direction of the compressor. 
     Here, the radial direction may refer to a direction (i.e., the lateral direction) perpendicular to the axial direction (i.e., the vertical direction). More specifically, the radial direction may refer to a direction extending inward from the outside outward from the inside with respect to the rotatory shaft. 
     As described above, when the eccentric portion  226   f  of the rotary shaft  226  is arranged through the head plate  245  of the orbiting scroll  240  to radially overlap the orbiting lap  241 , the repulsive force of the refrigerant and the compressive force may be applied to the same plane with respect to the third head plate  245 , and may thus be canceled to a certain degree. 
     The rotary shaft  226  may be coupled to the drive motor  220  and be provided with an oil supply passage  226   a  for guiding the oil contained in the oil reservoir space V 4  of the casing  210  upward. 
     Specifically, the upper portion of the rotary shaft  226  may be press-fitted to the center of the rotor  224 , and the lower portion thereof may be coupled to the compression unit  200  and supported in the radial direction. 
     Accordingly, the rotary shaft  226  may transmit the rotational power of the drive motor  220  to the orbiting scroll  240  of the compression unit  200 . Thereby, the orbiting scroll  240  eccentrically coupled to the rotary shaft  226  makes an orbiting movement with respect to the fixed scroll  250 . 
     The main journal  226   c  may be formed at a lower portion of the rotary shaft  226  so as to be inserted into the first bearing  232   a  of the main frame  230  and radially supported. The sub journal  226   g  may be formed at the lower portion of the main journal  226   c  so as to be inserted into the second bearing  252  of the fixed scroll  250  and radially supported. 
     The eccentric portion  226   f  may be formed between the main journal  226   c  and the sub journal  226   g  so as to be inserted into and coupled to the rotary shaft coupling portion  242  of the orbiting scroll  240 . 
     The main journal  226   c  and the sub-journal  226   g  may be coaxially arranged so as to have the same axial center. On the other hand, the eccentric portion  226   f  may be arranged so as to be eccentric in the radial direction with respect to the main journal  226   c  or the sub-journal  226   g.    
     For reference, the eccentric portion  226   f  may have an outer diameter less than the outer diameter of the main journal  226   c  and larger than an outer diameter of the sub-journal  226   g . In this case, the rotary shaft  226  may be easily coupled through the respective bearing accommodation portions  232   a  and  252  and the rotary shaft coupling portion  242 . 
     Alternatively, the eccentric portion  226   f  may not be integrated with the rotary shaft  226  but may be formed using a separate bearing. In this case, the outer diameter of the sub-journal  226   g  may not be less than the outer diameter of the eccentric portion  226   f,  and the rotation axis  226  may be inserted into and coupled to the respective bearing accommodation portions  232   a  and  252  and the rotary shaft coupling portion  242 . 
     An oil supply passage  226   a  for supplying the oil from the oil reservoir space V 4  to the outer circumferential surfaces of the rotary portions  226   c  and  226   g  and the outer circumferential surface of the eccentric portion  226   f  may be formed in the rotary shaft  226 . In addition, the rotary portions  226   c  and  226   g  and the eccentric portion  226   f  of the rotary shaft  226  may be provided with oil holes  228   a,    228   b,    228   d,  and  228   e  extending from the oil supply passage  226   a  to the outer circumferential surfaces in a penetrating manner. 
     For reference, the oil guided upward through the oil supply passage  226   a  may be discharged through the oil holes  228   a,    228   b,    228   d,  and  228   e  and supplied to the bearing surface or the like. 
     An oil feeder  271  for pumping the oil filling the oil reservoir space V 4  may be coupled to the lower end of the rotary shaft  226 , that is, the lower end of the sub-journal  226   g.    
     The oil feeder  271  may include an oil supply pipe  273  inserted into and coupled to the oil supply passage  226   a  of the rotary shaft  226 , and an oil intake member  274  inserted into the oil supply pipe  273  to suction the oil. 
     Here, the oil supply pipe  273  may be arranged through the through hole of the discharge cover  270  so as to be submerged in the oil reservoir space V 4 , and the oil intake member  274  may function like a propeller. 
     Although not shown in the drawings, a trochoid pump (not shown) may be provided in the sub journal  226   g  or the discharge cover  270  in place of the oil feeder  271  to forcibly pump the oil contained in the oil reservoir space V 4  upward. 
     Although not shown in the drawings, the scroll compressor according to the embodiment of the present invention may further include a first sealing member (not shown) for sealing the gap between the upper end of the main journal  226   c  and the upper end of the main frame  230 , and a second sealing member (not shown) for sealing the gap between the lower end of the sub-journal  226   g  and the lower end of the fixed scroll  250 . 
     For reference, with the first and second sealing members, the oil may be prevented from flowing out of the compression unit  200  along the bearing surface, thereby realizing a differential-pressure oil supply structure and preventing reverse flow of the refrigerant. 
     The rotor  224  or the rotary shaft  226  may be coupled with a balance weight  227  for suppressing noise vibration. 
     For reference, the balance weight  227  may be arranged in a space between the drive motor  220  and the compression unit  200 , that is, the second space V 2 . 
     Hereinafter, operation of the scroll compressor  1  according to the embodiment of the present invention will be described. 
     When power is applied to the drive motor  220  to generate a rotational force, the rotary shaft  226  coupled to the rotor  224  of the drive motor  220  begins to rotate. Then, the orbiting scroll  240  eccentrically coupled to the rotary shaft  226  is pivotally moved with respect to the fixed scroll  250  to form the compression chamber S 1  between the orbiting lap  241  and the fixed lap  251 . The compression chamber Si may be formed in several stages in succession as the volume gradually decreases toward the center. 
     The refrigerant supplied from the outside of the casing  210  through the refrigerant suction pipe  218  may be directly introduced into the compression chamber S 1 . The refrigerant may be compressed as it is moved toward the discharge chamber of the compression chamber S 1  by the orbiting motion of the orbiting scroll  240 . Then, the refrigerant may be discharged from the discharge chamber to the third space V 3  through the discharge port  253  of the fixed scroll  250 . 
     Thereafter, the compressed refrigerant discharged into the third space V 3  flows to the inner space of the casing  210  (i.e., the second space V 2  and the first space V 1 ) through the second discharge hole  256   b  and the first discharge hole  231   a,  and is then discharged from the casing  210  through the refrigerant discharge pipe  216 . 
     Here, the refrigerant discharged into the third space V 3  may be guided to the second discharge hole  256   b  by the discharge cover  270  without being leaked to the oil reservoir space V 4 . 
       FIGS. 4A to 6B  are views showing the rotary shaft  226  and bearing of the scroll compressor of the present invention. 
     The rotary shaft  226  is coupled to the drive motor  220  and is rotated by the rotational force of the drive motor  220  transmitted thereto. The rotary shaft  226  is arranged through the main frame  230 , the orbiting scroll  240 , the fixed scroll  250  and the discharge cover, and the lower end thereof is submerged in the oil reservoir space. The oil feeder  271  located at the lower end of the rotary shaft  226  submerged in the oil reservoir space suctions the oil in the oil reservoir space and supplies the oil to the oil supply passage  226   a  inside the rotary shaft  226 . The oil in the oil supply passage  226   a  is supplied to the journal bearing through the oil holes  228   a,    228   b,    228   d,  and  228   e  extending from the oil supply passage  226   a  to the outer circumferential surface in a penetrating manner, thereby enhancing the rotation operation between the rotary shaft  226  and the bearing. 
     Ball bearings are problematic in terms of durability and smooth rotation because the force is concentrated at specific contact points thereof. Accordingly, the scroll compressor of the present invention may employ a journal bearing, which enhances the rotational operation using oil between the bearing and the rotary shaft  226  such that force is uniformly applied along the circumference of the rotary shaft. The journal bearing is not fixed to the rotary shaft  226  but is spaced apart from the rotary shaft  226  by a predetermined distance. The main frame  230  and the fixed scroll  250 , which do not rotate, include a first bearing  232   a  and a second bearing  252  that are spaced apart from the rotary shaft  226  by a predetermined distance in order not to interfere with rotation of the rotary shaft  226 . 
     A portion of the rotary shaft  226  surrounded by the first bearing  232   a  is referred to as a main journal  226   c.  The rotary shaft  226  may rotate while the main journal  226   c  and the first bearing  232   a  are not in direct contact with each other but maintained at a predetermined distance from each other using the oil between the first bearing  232   a  and the main journal  226   c . The first bearing  232   a  and the main journal  226   c  constitute a first rotating portion. 
     Similarly, a portion of the rotary shaft  226  surrounded by the second bearing  252  is referred to as a sub-journal  226   g.  The rotary shaft  226  may rotate while the sub-journal  226   g  and the second bearing  252  are not in direct contact with each other but maintained at a predetermined distance from each other using the oil between the second bearing  252  and the sub-journal. The second bearing  252  and the sub-journal  226   g  constitute a second rotating portion. 
     As shown in  FIG. 1B , the first bearing  232   a  and the main journal  226   c  are spaced apart from each other and the second bearing  252  and the sub journal  226   g  are spaced apart from each other by a predetermined distance. 
     The eccentric portion  226   f  in a space between the first bearing  232   a  and the second bearing  252  where the orbiting scroll  240  is located has an asymmetric structure. Accordingly, when the rotary shaft  226  is rotated by the driving force of the drive unit, the eccentric portion  226   f  is slightly displaced from the center, and thus the rotary shaft  226  is bent as shown in  FIG. 2A . When the rotary shaft is bent, the first bearing  232   a  and the main journal  226   c  come into contact with each other to generate friction, and the second bearing  252  and the sub journal  226   g  come into contact with each other to generate friction, shown in  FIG. 2B . Thereby, rotation is not smoothly performed. 
     Since the eccentric portion  226   f  is biased to one side, the portions of the first bearing  232   a  and the second bearing  252  that come into contact with the main journal  226   c  and the sub journal  226   g  are closer to the eccentric portion  226   f.  That is, the lower portion of the first bearing  232   a  and the upper portion of the second bearing  252  come into contact with the journals. In order to address this issue, the first bearing  232   a  and the main journal  226   c  in the first rotating portion of the present invention may be arranged such that the gap therebetween varies according to a vertical position, and the second bearing  252  and the sub journal  226   g  in the second rotating portion are arranged such that the gap therebetween varies according to a vertical position. That is, the gap between the first bearing  232   a  and the main journal  226   c  is wider at a lower position than at a higher position, while the gap between the second bearing  252  and the sub journal  226   g  is narrower at a lower position than at an higher position. 
     In order to vary the gap between the first bearing  232   a  and the main journal  226   c  and the gap between the second bearing  252  and the sub journal  226   g  with a vertical position, the first bearing  232   a  and the second bearing  252  needs to be designed differently from the conventional cases, or the shape of the main journal  226   c  or the sub-journal  226   g  needs to be changed from the conventional shape. 
     As shown in  FIG. 4A , each of the first bearing  232   a  and the second bearing  252  may include a plurality of rings arranged in the vertical direction and having diameters different from each other. Since the first ring has a smaller diameter than the second ring, the gap between the main journal  226   c  or the sub journal  226   g  and the second ring is larger than the gap between the main journal  226   c  or the sub journal  226   g  and the first ring. The portion of the rotary shaft corresponding to the second ring is eccentrically rotated with respect to the center, and accordingly the second ring may be formed to be larger than the first ring to avoid contact between the rotary shaft and the bearing. 
     In the first bearing  232 , the first ring  2321  may be disposed on the second ring  2322 . In the second bearing  252 , the first ring  2521  is disposed under the second ring  2522 . 
     As shown in  FIG. 4B , the second rings  2322  and  2522  are larger than the conventional bearings, and accordingly may rotate without contacting the main journal  226   c  and the sub-journal  226   g.  Therefore, deterioration of the rotational force and durability caused by friction may be prevented, and noise may be reduced. 
     While one ring is provided per bearing in the present embodiment, a plurality of rings may be used per bearing, and the first ring and the second ring may be configured as independent rings. The rings may also be formed to have steps on the inner side surfaces thereof. The number of steps may not be two but may be greater than or equal three. The steps may have different heights. 
     As shown in  FIG. 5A , the first bearing  232   a  and the second bearing  252  may have inclined surfaces in the vertical direction. The inclined surface of the first bearing  232   a  may have a narrow upper portion and a wide lower portion. The inclined surface of the second bearing  252  may have a wide upper portion and a narrow lower portion. The gap between the first bearing  232   a  and the main journal  226   c  and the gap between the second bearing  252  and the sub journal  226   g  may be varied with a vertical position by the inclined surfaces of the first bearing  232   a  and the second bearing  252 . 
     As shown in  FIG. 5B , even when the rotary shaft rotates, the lower portion of the first bearing  232   a  may not touch the main journal  226   c,  and the upper portion of the second bearing  252  may not touch the sub journal  226   g.  Accordingly, deterioration of the rotational force and durability caused by friction may be prevented, and noise may be reduced. 
     The inclined surface of the bearing may have the same slope from the upper portion to the lower portion of the bearing. Alternatively, the inclined surface may have a slop varying with the position, or the inclined surface may be curved. 
     As shown in  FIG. 6A , the diameters of first bearing  232   a  and the second bearing  252  may be constant, but the diameters of the main journal  226   c  and the sub-journal  226   g  may vary between the upper portions and lower portions of the main journal  226   c  and the sub journal  226   g.  In contrast with the case of  FIG. 5A , and inclined surfaces may be formed on the rotary shaft  226  such that the upper portion of the main journal  226   c  has a larger diameter than the lower portion of the main journal  226   c,  and the upper portion of the sub journal  226   g  has a smaller diameter than the lower portion of the sub journal  226   g.  Thus, the gap between the first bearing  232   a  and the main journal  226   c  and the gap between the second bearing  252  and the sub-journal  226   g  may vary with a vertical position. 
     As the gap between the first bearing  232   a  and the main journal  226   c  and the gap between the second bearing  252  and the sub journal  226   g  are formed to vary with a vertical position as described above, degradation of the performance of the first bearing  232   a  and the second bearing  252  due to deflection of the rotary shaft  226 , which occurs when the orbiting scroll  240  is rotated according to rotation of the rotary shaft  226 , may be addressed. 
     In the embodiments described above, the first bearing  232   a  and the second bearing  252  are vertically symmetric with respect to the eccentric portion  226   f,  but they are not necessarily required to have a symmetrical structure. The embodiments of  FIGS. 4A to 6B  may be used in combination. 
     For example, the first bearing  232   a  may be composed of a first ring  2321  and a second ring  2322  which have different diameters, and the second bearing  252  may have an inclined inner surface. 
     As described above, the scroll compressor  1  according to the present invention may prevent an eccentric effect occurring during rotation of the rotary shaft  226  from lowering performance of the bearing, thereby preventing noise and degradation of compression performance. 
     Further, friction, which lowers durability, may be prevented, thereby increasing the service life of the compressor  1  and reducing the maintenance cost. 
     As apparent from the above description, the present invention has effects as follows. 
     The scroll compressor according to the present invention may prevent performance of the bearing from being deteriorated due to the eccentric effect occurring during rotation of the rotary shaft, thereby preventing noise from being generated and preventing compression performance from being degraded. 
     Further, friction may be prevented from deteriorating durability, thereby increasing the service life of the compressor and reducing the maintenance cost. 
     The above and other objects, features and advantages of the present invention are more apparent from the detailed description taken in conjunction with the accompanying drawings. 
     It will be apparent to those skilled in the art that various substitutions, modifications, and variations can be made in the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. Therefore, the present invention is not limited by the above-described embodiments and the accompanying drawings.