Abstract:
A scroll compressor ( 10 ), comprising a fixed scroll ( 150 ), a movable scroll ( 160 ) and a drive shaft ( 30 ); the scroll compressor ( 10 ) further comprises a movable scroll counterweight ( 40 ); the movable scroll counterweight ( 40 ) is configured to rotate with the drive shaft ( 30 ); and the centrifugal force of the movable scroll counterweight ( 40 ) caused by the rotation acts on the hub ( 162 ) of the movable scroll ( 160 ). The above structure can effectively reduce the impact of the centrifugal force of the movable scroll on the radial seal of a scroll component, thus achieving proper radial sealing force between the fixed scroll and the movable scroll at any rotating speed.

Description:
CROSS REFERENCE OF RELEVANT APPLICATION 
     This application is the national phase of International Application No. PCT/CN2013/073917, titled “SCROLL COMPRESSOR”, filed on Apr. 9, 2013, which claims priority to the Chinese patent application No. 201210105213.1 titled “scroll compressor” and filed with the Chinese Patent Office on Apr. 11, 2012, to the Chinese patent application No. 201220151455.X titled “scroll compressor” and filed with the Chinese Patent Office on Apr. 11, 2012, to the Chinese patent application No. 201310045737.0 titled “scroll compressor” and filed with the Chinese Patent Office on Feb. 5, 2013, and to the Chinese patent application No. 201320067054.0 titled “scroll compressor” and filed with the Chinese Patent Office on Feb. 5, 2013, the disclosures of which are incorporated herein by reference in their entireties. 
     FIELD 
     The present application relates to a scroll compressor. 
     BACKGROUND 
     The descriptions in this section merely provide background information related to the present disclosure, which may not necessarily constitute the prior art. 
     As shown in  FIG. 1 , a conventional scroll compressor  100  generally includes a housing  110 , a top cover  112  provided at one end of the housing  110 , a bottom cover  114  provided at the other end of the housing  110 , and a partition plate  116  which is provided between the top cover  112  and the housing  110  so as to divide an interior space of the compressor into a high-pressure side and a low-pressure side. The high-pressure side is defined between the partition plate  116  and the top cover  112 , and the low-pressure side is defined among the partition plate  116 , the housing  110  and the bottom cover  114 . An inlet  118  for inflowing the fluid is provided on the low-pressure side, and an outlet  119  for discharging the compressed fluid is provided on the high-pressure side. An electric motor  120 , including a stator  122  and a rotor  124 , is provided in the housing  110 . A driving shaft  130  is provided in the rotor  124  to drive a compression mechanism including a fixed scroll  150  and a movable scroll  160 . The movable scroll  160  includes an end plate  164 , a hub portion  162  formed on one side of the end plate and a spiral wrap  166  formed on the other side of the end plate. The fixed scroll  150  includes an end plate  154 , a spiral wrap  156  formed on one side of the end plate and a discharge port  152  formed approximately at the center of the end plate. A series of compression pockets C1, C2 and C3, the volumes of which are reduced from outside to inside in a radial direction, are formed between the spiral wrap  156  of the fixed scroll  150  and the spiral wrap  166  of the movable scroll  160 . The radial outermost compression pocket C1 side is at the intake pressure, and the radial innermost compression pocket C3 side is at the discharge pressure. The intermediate compression pocket C2 is between the intake pressure and the discharge pressure, thereby being also called a medium pressure pocket. 
     The movable scroll  160  is supported at one side by the upper portion of a main bearing housing  140  (which forms a thrust member), and the driving shaft  130  is supported at one end by a main bearing  144  provided in the main bearing housing  140 . An eccentric crank pin  132  is provided on one end of the driving shaft  130 , and an unloading bushing  142  is provided between the eccentric crank pin  132  and the hub portion  162  of the movable scroll  160 . Under the driving of the motor  120 , the movable scroll  160  will orbit relative to the fixed scroll  150  (i.e., a central axis of the movable scroll  160  rotates about a central axis of the fixed scroll  150 , but the movable scroll  160  does not rotate about its own central axis) to compress fluid. The orbiting is achieved through an Oldham coupling  190  disposed between the fixed scroll  150  and the movable scroll  160 . The fluid compressed by the fixed scroll  150  and the movable scroll  160  is discharged to the high-pressure side through the discharge port  152 . To prevent the backflow of the fluid at the high-pressure side to the low-pressure side via the discharge port  152  in particular cases, a check valve or discharge valve  170  is provided at the discharge port  152 . 
     To compress fluid, it is necessary to have an effective seal between the fixed scroll  150  and the movable scroll  160 . On the one hand, it is necessary to have an axial seal between a top end of the spiral wrap  156  of the fixed scroll  150  and the end plate  164  of the movable scroll  160  and between a top end of the spiral wrap  166  of the movable scroll  160  and the end plate  154  of the fixed scroll  150 . 
     Generally, a backpressure pocket  158  is provided on the side of the end plate  154  of the fixed scroll  150  opposite to the spiral wrap  156 . A seal assembly  180  is provided in the backpressure pocket  158 , and the partition plate  116  limits an axial displacement of the seal assembly  180 . The backpressure pocket  158  is in fluid communication with the intermediate pressure pocket C2 through an axially extending through-hole (not shown) formed in the end plate  154  so as to generate a force for pressing the fixed scroll  150  towards the movable scroll  160 . Since the movable scroll  160  is supported at one side by the upper portion of the main bearing housing  140 , the pressure in the backpressure pocket  158  may be applied to effectively press the fixed scroll  150  and the movable scroll  160  towards each other. When the pressures in various compression pockets exceed a predetermined value, the resultant force generated from the pressures in the compression pockets will larger than the downward pressing force provided in the backpressure pocket  158  so as to allow the fixed scroll  150  to move upwardly. At this time, the fluid in the compression pockets will leak to the low-pressure side for unloading through a gap between the top end of the spiral wrap  156  of the fixed scroll  150  and the end plate  164  of the movable scroll  160  and a gap between the top end of the spiral wrap  166  of the movable scroll  160  and the end plate  154  of the fixed scroll  150 , thereby providing an axial flexibility for the scroll compressor. 
     On the other hand, it is necessary to have a radial seal between a side surface of the spiral wrap  156  of the fixed scroll  150  and a side surface of the spiral wrap  166  of the movable scroll  160 . Such radial seal between them is generally achieved by means of a centrifugal force of the movable scroll  160  in operation and a driving force provided by the driving shaft  130 . Specifically, in operation, under the driving of the electric motor  120 , the movable scroll  160  will orbit relative to the fixed scroll  150  (i.e., a central axis of the movable scroll  160  rotates about a central axis of the fixed scroll  150 , but the movable scroll  160  does not rotate about its own central axis), and thus will generate the centrifugal force. Additionally, the eccentric crank pin  132  of the driving shaft  130  may generate a driving force component contributing to achieve the radial seal between the fixed scroll and the movable scroll during rotation. The spiral wrap  166  of the movable scroll  160  will be brought into abutment against the spiral wrap  156  of the fixed scroll  150  by means of the centrifugal force and the driving force component, thereby achieving a radial seal between them. When incompressible materials (such as solid impurities, lubricating oil and liquid refrigerant) enter the compression pocket and get stuck between the spiral wrap  156  and the spiral wrap  166 , the spiral wrap  156  and the spiral wrap  166  may temporarily separate from each other in the radial direction to allow foreign matters to pass therethrough, thereby preventing the damage of the spiral wrap  156  or  166 . This ability to radially separate provides a radial flexible for the scroll compressor, improving the reliability of the compressor. 
     However, there are the following problems as a result of the radial seal achieved by the centrifugal force as described above.  FIG. 2  shows a schematic view of a radial seal force between a fixed scroll  150  and a movable scroll  160 . As shown in  FIG. 2 , a total radial seal force between the fixed scroll  150  and the movable scroll  160  may be represented by the formula:
 
 F   flank   =F   IOS   +F   s  Sin θ eff   −F   IO *Sin θ− F   rg   formula (1)
 
     where 
     F flank  is a total radial seal force between the fixed scroll  150  and the movable scroll  160 ; 
     F IOS  is the centrifugal force of the movable scroll  160 ; 
     F s  Sin θ eff  is the driving force component provided by the eccentric crank pin  132 , wherein F s  is the total driving force provided by the eccentric crank pin  132 , and θ eff  is the effective driving angle of the eccentric crank pin  132 ; 
     F IO *Sin θ is the centrifugal force component provided by the Oldham coupling  190 , wherein F IO  is the total centrifugal force provided by the Oldham coupling  190 , θ is an angle of the movable scroll  160  oriented relative to the fixed scroll  150 ; 
     F rg  is the radial gas force provided by the fluid in the compression pockets. 
     As can be seen from the above formula 1, F IOS  and F IO *Sin θ are items related to the rotational speed of the driving shaft  130 , whereas F s  Sin θ eff  and F rg  are items independent of the rotational speed of the driving shaft  130 . Thus, the radial seal force F flank  is related to the rotational speed of the driving shaft  130 . That is, the greater the rotational speed of the driving shaft  130  is, the greater the radial seal force F flank  is, and the smaller the rotational speed of the driving shaft  130  is, the smaller the radial seal force F flank  is. Therefore, when the scroll compressor  100  is operated at a low rotational speed, the radial seal force F flank  between the fixed scroll  150  and the movable scroll  160  may be insufficient, thereby resulting in a reduced efficiency of the compressor, whereas when the scroll compressor  100  is operated at a high rotational speed, the radial seal force F flank  between the fixed scroll  150  and the movable scroll  160  may be excessively large, thereby causing an excessive wear of the scroll components. 
     Therefore, there is a need for a scroll compressor which can ensure a radial seal both at a low speed and at a high speed in operation. 
     SUMMARY 
     An object of one or more embodiments of the present application is to provide a scroll compressor which can ensure a radial seal both under low speed condition and under high speed condition. 
     An another object of one or more embodiments of the present application is to provide a scroll compressor which can ensure a radial seal while having a simple structure. 
     In order to achieve one or more of the above-mentioned objects, according to one aspect of the present application, there is provided a scroll compressor, including a fixed scroll, a movable scroll and a driving shaft. The fixed scroll includes a fixed scroll end plate and a fixed scroll wrap formed on one side of the fixed scroll end plate. The movable scroll includes a movable scroll end plate, a movable scroll wrap formed on one side of the movable scroll end plate and a hub portion formed on the other side of the movable scroll end plate. The driving shaft includes an eccentric crank pin, and the eccentric crank pin is fitted in the hub portion of the movable scroll for driving the movable scroll. The scroll compressor further includes a movable scroll counterweight. The movable scroll counterweight is configured to be able to rotate with the driving shaft and to generate a centrifugal force by the rotation which acts on the hub portion of the movable scroll. 
     Preferably, the direction of the centrifugal force of the movable scroll counterweight is substantially opposite to the direction of the centrifugal force of the movable scroll. 
     Preferably, the centrifugal force of the movable scroll counterweight is arranged to be approximately equal to the centrifugal force of the movable scroll. 
     Preferably, the movable scroll counterweight comprises a cylindrical portion provided around the hub portion of the movable scroll, and at least a portion of the cylindrical portion contacts an outer side of the hub portion. 
     Preferably, a bearing is provided in the cylindrical portion of the movable scroll counterweight, and an inner side of the bearing contacts the outer side of the hub portion. 
     Preferably, the bearing is a rolling bearing or a sliding bearing. 
     Preferably, a driving portion for driving the rotation of the movable scroll counterweight is provided on an outer peripheral surface of the driving shaft. The movable scroll counterweight includes a bottom wall, and a driving hole for being fitted with the driving portion is provided in the bottom wall. 
     Preferably, the driving portion has a shape substantially corresponding to a shape of the driving hole. 
     Preferably, the driving portion has a non-circular cross-section. 
     Preferably, a maximum size of the driving portion in a radial direction is less than or equal to a maximum size of the driving hole in the radial direction. 
     Preferably, the driving portion and the driving hole are configured to allow the movable scroll counterweight to slide on the driving portion in the radial direction. 
     Preferably, the driving portion includes two step portions each including a bottom surface and a side surface, and the side surfaces of the two step portions are parallel to one another. 
     Preferably, the driving hole has two side walls able to be fitted with the side surfaces of the two step portions. 
     Preferably, the two side walls of the driving hole are parallel to one another. 
     Preferably, wherein the side surfaces of the step portions are substantially parallel to the direction of the centrifugal force of the movable scroll. 
     Preferably, a distance between the side surfaces of two step portions is substantially equal to a distance between the two side walls of the driving hole of the movable scroll counterweight. 
     Preferably, the movable scroll counterweight is supported in an axial direction by a bottom surface of at least one of the step portions of the driving shaft. 
     Preferably, the eccentric crank pin of the driving shaft is fitted in the hub portion of the movable scroll via an unloading bushing. The eccentric crank pin includes a planar portion extending parallel to a rotational axis of the driving shaft, and the unloading bushing includes a planar portion corresponding to the planar portion of the eccentric crank pin. 
     Preferably, if a gap between the eccentric crank pin and the unloading bushing in the radial direction parallel to the planar portion of the eccentric crank pin is C1, and if a gap between the driving shaft and the driving hole of the movable scroll counterweight in the radial direction parallel to side walls of the driving hole is C2, then the relationship between C1 and C2 is set as C2≧C1. 
     Preferably, the center of gravity of the movable scroll counterweight and the center of gravity of the movable scroll are located on opposite sides of the rotational axis of the driving shaft. 
     Preferably, if the mass of the movable scroll is M1 and the minimum orbiting radius of the movable scroll is D1, and if the mass of the movable scroll counterweight is M2 and the maximum orbiting radius of the centroid of said movable scroll counterweight is D2, then the parameters described above are set to satisfy the formula: M1*D1≧M2*D2. 
     Preferably, if a distance between the center of gravity of the movable scroll and the rotational axis of the driving shaft is d1 during a normal operation of the scroll compressor, then D1=d1−C1; and if a distance between the center of gravity of the movable scroll counterweight and the rotational axis of the driving shaft is d2 during a normal operation of the scroll compressor, then D2=d2+C1. 
     Preferably, a matched hole is provided in the outer peripheral surface of the driving shaft. A driving hole is formed in the bottom wall of the movable scroll counterweight. The scroll compressor further includes a driving rod having a first end fitted in the matched hole of the driving shaft and a second end fitted in the driving hole of the movable scroll counterweight. 
     Preferably, the scroll compressor further includes a snap spring allowing the movable scroll counterweight to be fixedly fitted in the hub portion of the movable scroll. 
     Preferably, the driving hole is an elongated hole substantially extending in the radial direction of the movable scroll counterweight. 
     Preferably, if a gap between the eccentric crank pin and the unloading bushing in a radial direction parallel to the planar portion of the eccentric crank pin is C1, and if a radial length of the elongated hole is C3, then the relationship between C1 and C3 is set as C3≧C1. 
     Preferably, the driving rod is substantially L-shaped. 
     Preferably, the scroll compressor further includes a main bearing housing for supporting the driving shaft and a thrust plate for supporting the end plate of the movable scroll. The main bearing housing and the thrust plate are separate components and fixed together by a fastening device. 
     Preferably, a space for rotation of the movable scroll counterweight is formed between the main bearing housing and the thrust plate. 
     Preferably, the scroll compressor further includes a main bearing housing for supporting the driving shaft and a thrust plate for supporting the end plate of the movable scroll. The main bearing housing and the thrust plate are integrally formed. 
     Preferably, the movable scroll counterweight includes a cylindrical portion disposed around the hub portion of the movable scroll, and at least one oil supply groove is provided on an inner circumference of the cylindrical portion. 
     Preferably, the oil supply groove substantially extends in the axial direction of the scroll compressor. 
     Preferably, a pair of the oil supply grooves are provided. 
     Preferably, the pair of the oil supply grooves are arranged substantially symmetrically with respect to the rotation center of the movable scroll counterweight. 
     Preferably, a portion, in which the oil supply groove is provided, of the cylindrical portion of the movable scroll counterweight is higher than the other portions of the cylindrical portion. 
     Preferably, a portion, in which the oil supply groove is provided, of the cylindrical portion of the movable scroll counterweight is configured to be adjacent to a lower surface of the movable scroll end plate. 
     Preferably, the movable scroll counterweight further includes a bottom wall, and the bottom wall is formed thereon with a step portion protruding from the bottom wall. 
     Preferably, the oil supply groove extends to the step portion in the axial direction. 
     Preferably, the height of the step portion protruded relative to the bottom wall is set such that a ratio of the lubricant flowing upwardly through the oil supply groove to the lubricant flowing downwardly through a driving hole formed in the bottom wall can reach a predetermined value. 
     The scroll compressor according to one or more embodiments of the present application has following advantageous. 
     In a scroll compressor according to an embodiment of the present application, a movable scroll counterweight is provided, and configured to be able to rotate with the driving shaft and to generate the centrifugal force under the rotation which acts on the hub portion of the movable scroll. In addition, the direction of the centrifugal force of the movable scroll counterweight may be set to be substantially opposite to the direction of the centrifugal force of the movable scroll. Accordingly, the centrifugal force of the movable scroll can be balanced by the centrifugal force of the movable scroll counterweight. Thus, a radial seal force between the movable scroll and the fixed scroll will depend primarily on a driving force provided by the eccentric crank pin of the driving shaft. Since the driving force provided by the eccentric crank pin is independent of the rotational speed of the driving shaft, by presetting the driving force of the eccentric crank pin to be a proper value, a radial sealing force between the two scroll components can be maintained properly whether the scroll compressor is running at a low speed or running at a high speed. 
     In a scroll compressor according to an embodiment of the present application, the centrifugal force of the movable scroll counterweight may be set substantially equal to the centrifugal force of the movable scroll. Accordingly, the centrifugal force of the movable scroll can be completely counteracted by the movable scroll counterweight. Thus, it is possible to ensure that a radial sealing force between the two scroll components remains substantially constant at various rotational speeds, so that the scroll compressor can operate stably under various conditions. 
     In a scroll compressor according to an embodiment of the present application, the movable scroll counterweight can include a cylindrical portion disposed to surround the hub portion of the movable scroll, and at least a portion of the cylindrical portion contacts an outer side of the hub portion. With this construction, the counterweight mechanism is easier to be manufactured and installed, thus enabling to simplify the structure of a scroll compressor and to reduce its manufacturing cost. 
     In a scroll compressor according to an embodiment of the present application, the cylindrical portion of the movable scroll counterweight may be provided therein with a bearing, and an inner side of the bearing contacts the outer side of the hub portion. Preferably, the bearing may be a rolling bearing or a sliding bearing. With this construction, it is possible to make the transmission of the force between the movable scroll counterweight and the hub portion of the movable scroll smoother, and it is possible to reduce wear therebetween. 
     In a scroll compressor according to an embodiment of the present application, a driving portion for driving the movable scroll counterweight to rotate is provided on the outer peripheral surface of the driving shaft, and the movable scroll counterweight includes a bottom wall that is provided therein with a driving hole fitted with the driving portion. Thus, the driving shaft can easily drive the movable scroll counterweight to rotate together. Preferably, the driving portion may have a shape substantially corresponding to the shape of the driving hole, for example, the driving portion may have a non-circular cross-section. In practice, the driving portion and the driving hole may be of any construction that enables the cooperation therebetween to perform the power transmission. 
     In a scroll compressor according to an embodiment of the present application, the maximum size of the driving portion in radial direction may be set to be equal to or smaller than the maximum size of the driving hole in the radial direction. In particular, the driving portion and the driving hole are configured to allow the movable scroll counterweight to slide on the driving portion in the radial direction. Thus, in the case where the centrifugal force of the fixed scroll is counteracted, a radial flexibility still can be provided for the compressor. 
     In a scroll compressor according to an embodiment of the present application, the driving portion includes two step portions each including a bottom surface and a side surface, and the side surfaces of the two step portions are parallel to one another. Further, the driving hole has two side walls able to be fitted with the side surfaces of the two step portions. With the above construction, the driving shaft can easily and conveniently drive the movable scroll counterweight to rotate synchronously with the movable scroll so as to stably counteract the centrifugal force of the movable scroll. 
     In a scroll compressor according to an embodiment of the present application, a side surface of each step portion may be substantially parallel to the direction of the centrifugal force of the movable scroll. Thus, the movable scroll counterweight is to generate the centrifugal force only in the radial direction without a component of the force in other directions, which further simplifies the design of the movable scroll counterweight. Furthermore, a distance between the side surfaces of the two step portions may be substantially equal to a distance between the two side walls of the driving hole of the movable scroll counterweight. Therefore, when the driving shaft starts to rotate or stops rotating, there is no collision between the driving shaft and the movable scroll counterweight, thus avoiding noises to be generated therebetween. 
     In a scroll compressor according to an embodiment of the present application, the movable scroll counterweight is supported in the axial direction by a bottom surface of at least one of the step portions of the driving shaft. In other words, the movable scroll counterweight can rest directly on the bottom surface of the at least one of the step portions of the driving shaft, without the need for providing other members for holding the movable scroll counterweight axially, thereby simplifying the structure of the counterweight mechanism. 
     In a scroll compressor according to an embodiment of the present application, the eccentric crank pin of the driving shaft may be fitted in the hub portion of the movable scroll via an unloading bushing. In this case, if a gap between the eccentric crank pin and the unloading bushing in a radial direction parallel to the planar portion of the eccentric crank pin is C1, and if a gap between the driving shaft and the driving hole of the movable scroll counterweight in a radial direction parallel to the side walls of the driving hole is C2, then the relationship between C1 and C2 is set as C2≧C1. With this construction, it is possible to ensure that the compressor provided with the movable scroll counterweight still has its existing radial flexibility. 
     In a scroll compressor according to an embodiment of the present application, the center of gravity of the movable scroll counterweight and the center of gravity of the movable scroll can be located at opposite sides of the rotational axis of the driving shaft. In this case, if the mass of the movable scroll is M1 and the minimum orbiting radius of the movable scroll is D1, and if the mass of the movable scroll counterweight is M2 and the maximum orbiting radius of the centroid (or center of mass) of the movable scroll counterweight is D2, the above parameters are set to meet formula: M1*D1≧M2*D2. If a distance between the center of gravity of the movable scroll and the rotational axis of the driving shaft is d1 in a normal operation process of the scroll compressor, then D1=d1−C1. And, if the distance between the center of gravity of the movable scroll counterweight and the rotational axis of the driving shaft is d2 in a normal operation process of the scroll compressor, then D2=d2+C1. The above parameters further clarify the relationship between the geometric parameters of the movable scroll counterweight and the movable scroll, thus greatly facilitating the design of the movable scroll counterweight. 
     In a scroll compressor according to an embodiment of the present application, a matched hole is provided in the outer peripheral surface of the driving shaft, and a driving hole can be formed in the bottom wall of the movable scroll counterweight. The scroll compressor may further include a driving rod having a first end fitted in the matched hole of the driving shaft and a second end fitted in the driving hole of the movable scroll counterweight. With this construction, the driving shaft can easily and conveniently drive the movable scroll counterweight to synchronously rotate with the movable scroll, thereby counteracting stably the centrifugal force of the movable scroll. 
     In a scroll compressor according to an embodiment of the present application, the scroll compressor may further include a snap spring by which the movable scroll counterweight is fixedly fitted on the hub portion of the movable scroll. Therefore, the structure of the counterweight mechanism is relatively simple, and is assembled easily. 
     In a scroll compressor according to an embodiment of the present application, the driving hole may be an elongated hole substantially extending in the radial direction of the movable scroll counterweight. In addition, if a gap between the eccentric crank pin and the unloading bushing in a radial direction parallel to the planar portion of the eccentric crank pin is C1, and if a radial length of the elongated hole is C3, then the relationship between C1 and C3 is set as C3≧C1. With this construction, it is ensured that the scroll compressor provided with the movable scroll counterweight still has its existing radial flexibility. 
     In a scroll compressor according to an embodiment of the present application, a space for rotation of the movable scroll counterweight may be formed between the main bearing housing and the thrust plate. In other words, there is only a need for simple modification to the main bearing housing, or there is no need for modification to the main bearing housing (for example, the volume of the movable scroll counterweight is set to be suitable for rotation of the movable scroll counterweight in the existing space of the main bearing housing). Thus, the movable scroll counterweight may simply be configured. In addition, the main bearing housing and the thrust plate may be integrally formed, or may be formed as separate components and then be fixed together by a fastening device. With these constructions, the flexibility of the design of the movable scroll counterweight increases. In addition, in the case that the main bearing housing and the thrust plate are separate components, the thrust plate may be designed appropriately such as to provide the movable scroll with a thrust surface having a greater area, so as to increase the stability and durability of the operation of the scroll compressor. 
     In a scroll compressor according to an embodiment of the present application, at least one oil supply groove is provided on an inner circumference of the cylindrical portion of the movable scroll counterweight. Lubricant can be easily and reliably supplied onto the thrust surfaces between the end plate of the movable scroll and the thrust plate through the oil supply groove, so as to achieve a better lubrication. In addition, the portion of the cylindrical portion in which the oil supply groove is provided may be higher than the other portions of the cylindrical portion, or the portion of the cylindrical portion in which the oil supply groove is provided can be constructed to be adjacent to a lower surface of the end plate of the movable scroll, thereby facilitating the supply of lubricant to the thrust surface of the movable scroll with ease. Further, a step portion may be formed at the bottom wall of the movable scroll counterweight. A ratio of the lubricant flowing upwardly through the oil supply grooves to the lubricant flowing downwardly through the driving hole formed in the bottom wall can be controlled by using the step portion, so as to realize a reasonable supply of the lubricant to various parts that need be lubricated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of one or more embodiments of the present application will become more apparent from the following description with reference to the accompanying drawings, wherein: 
         FIG. 1  is a longitudinal sectional view of a conventional scroll compressor; 
         FIG. 2  is a schematic view of a radial seal force between a movable scroll and a fixed scroll of  FIG. 1 ; 
         FIG. 3  shows a longitudinal sectional view of a scroll compressor according to a first embodiment of the application; 
         FIG. 4  shows an exploded perspective view of associated components surrounding a movable scroll counterweight according to the first embodiment of the application; 
         FIG. 5  shows an assembled perspective view of the components shown in  FIG. 4 ; 
         FIG. 6A  is a perspective view of a driving shaft according to the first embodiment of the application,  FIG. 6B  is another perspective view of the driving shaft, and  FIG. 6C  is an end view of the driving shaft; 
         FIG. 7A  is a perspective view of a movable scroll counterweight according to the first embodiment of the application, and  FIG. 7B  is a longitudinal sectional view of the movable scroll counterweight; 
         FIG. 8A  is a perspective view of a main bearing housing and a thrust plate according to the first embodiment of the application, and  FIG. 8B  is a partial sectional perspective view of the main bearing housing and the thrust plate; 
         FIG. 9  is an enlarged longitudinal sectional view of surroundings of the movable scroll counterweight according to the first embodiment of the application; 
         FIG. 10  is a plan sectional view taken along line A-A shown in  FIG. 9 ; 
         FIG. 11  is a partial enlarged view of  FIG. 10  showing the relationship among a driving shaft, a movable scroll counterweight and an unloading bushing; 
         FIG. 12  is a schematic view of a radial seal force between a movable scroll and a fixed scroll according to the first embodiment of the application; 
         FIG. 13  is a schematic view of the relationship of the mass and the orbiting radius between the movable scroll and the movable scroll counterweight; 
         FIG. 14  shows a partial longitudinal sectional view of a scroll compressor according to a modification of the first embodiment of the application; 
         FIG. 15A  and  FIG. 15B  show perspective views of a movable scroll counterweight according to a modification of the first embodiment of the application viewed from different directions; 
         FIG. 16  shows a partial longitudinal sectional view of a scroll compressor according to a second embodiment of the application; 
         FIG. 17A  and  FIG. 17B  show perspective views of a movable scroll counterweight according to the second embodiment of the application viewed from different directions; 
         FIG. 18  shows a perspective view of a driving shaft according to the second embodiment of the application; 
         FIG. 19  shows a perspective view of a driving rod according to the second embodiment of the application; 
         FIG. 20  shows a perspective view of a snap spring according to the second embodiment of the application; 
         FIG. 21A  and  FIG. 21B  show perspective views of a movable scroll counterweight according to a modification of the second embodiment of the application viewed from different directions; 
         FIG. 22  shows a schematic view of the supply of lubricant in the scroll compressor according to the first embodiment of the application. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of preferred embodiments is only exemplary, and is never a limitation to the present application and its application or usage. 
     An identical reference numeral is adopted to represent an identical component throughout the accompanying drawings. Therefore, the constructions of the same components will no longer be repeated in this description. 
     The basic structure and principle of a scroll compressor  10  according to the first embodiment of the application will be described below with reference to  FIG. 3-13 . 
     As shown in  FIG. 3 , the scroll compressor  10  according to an embodiment of the present application generally includes a housing  110 , a top cover  112  arranged at one end of the housing  110 , a bottom cover  114  arranged on the other end of the housing  110 , and a partition plate  116  arranged between the top cover  112  and the housing  110  to divide an inner space of the compressor into a high-pressure side and a low-pressure side. The high-pressure side is defined between the partition plate  116  and the top cover  112 , and the low-pressure side is defined among the partition plate  116 , the housing  110  and the bottom cover  114 . An inlet  118  for inflowing the fluid is provided on the low-pressure side, and an outlet  119  for discharging the compressed fluid is provided on the high-pressure side. An electric motor  120 , including a stator  122  and a rotor  124 , is provided in the housing  110 . A driving shaft  130  is provided in the rotor  124  to drive a compression mechanism including a fixed scroll  150  and a movable scroll  160 . The movable scroll  160  includes an end plate  164 , a hub portion  162  formed on one side of the end plate and a spiral wrap  166  formed on the other side of the end plate. The fixed scroll  150  includes an end plate  154 , a spiral wrap  156  formed on one side of the end plate and an discharge port  152  formed approximately at the center of the end plate. 
     A series of compression pockets C1, C2 and C3, the volumes of which are reduced from outside to inside in a radial direction, are formed between the spiral wrap  156  of the fixed scroll  150  and the spiral wrap  166  of the movable scroll  160 . The radial outermost compression pocket C1 is at the intake pressure, and the radial innermost compression pocket C3 is at the discharge pressure. The intermediate compression pocket C2 is between the intake pressure and the discharge pressure, thereby being also called medium pressure pocket. 
     A portion of the driving shaft  30  is supported by a main bearing  144  arranged in a main bearing housing  20 . One end of driving shaft  30  is formed with an eccentric crank pin  32 . The eccentric crank pin  32  is fitted in a hub portion  162  of the movable scroll  160  via an unloading bushing  60  so as to drive the movable scroll  160 . As shown in  FIG. 11 , the eccentric crank pin  32  includes a planar portion  321  extending in parallel to the rotational axis of the driving shaft  30 , and the unloading bushing  60  includes a planar portion  62  corresponding to the planar portion  321  of the eccentric crank pin. 
     A thrust plate  50  is provided on the main bearing housing  20 . The thrust plate  50  can be fixed on the main bearing housing  20  by a fastening device (referring to  FIGS. 8A and 8B ). A space S is formed between the main bearing housing  20  and the thrust plate  50 . The movable scroll  160  is supported at one side by the thrust plate  50 . Under the driving of the electric motor  120 , the movable scroll  160  will orbit with respect to the fixed scroll  150  (i.e., the central axis of the movable scroll  160  rotates around the central axis of the fixed scroll  150 , but the movable scroll  160  cannot rotate around its own central axis) to compress fluid. The orbiting is realized by the Oldham coupling  190  arranged between the fixed scroll  150  and the movable scroll  160 . The fluid compressed by the fixed scroll  150  and the movable scroll  160  is discharged to the high-pressure side through the discharge port  152 . To prevent the backflow of the fluid at the high-pressure side to the low-pressure side via the discharge port  152  in particular cases, a check valve or discharge valve  170  is provided at the discharge port  152 . 
     To achieve an axial seal between a top end of the spiral wrap  156  of the fixed scroll  150  and the end plate  164  of the movable scroll  160  and an axial seal between a top end of the spiral wrap  166  of the movable scroll  160  and the end plate  154  of the fixed scroll  150 . Generally, a backpressure pocket  158  is provided on a side of the end plate  154  of the fixed scroll  150  opposite to the spiral wrap  156 . A seal assembly  180  is provided in the backpressure pocket  158 , and an axial displacement of the seal assembly  180  is limited by the partition plate  116 . The backpressure pocket  158  is in fluid communication with the intermediate pressure pocket C2 through an axially extending through-hole (not shown) formed in the end plate  154  so as to generate a force for pressing the fixed scroll  150  towards the movable scroll  160 . Since the movable scroll  160  is supported on one side by an upper portion of the main bearing housing  140 , the pressure in the backpressure pocket  158  may be employed to effectively press the fixed scroll  150  and the movable scroll  160  towards each other. When the pressures in various compression pockets exceed a predetermined value, the resultant force generated from the pressures in the compression pockets will larger than the downward pressing force provided in the backpressure pocket  158  so as to allow the fixed scroll  150  to move upwardly. At this time, the fluid in the compression pockets will leak to the low-pressure side for unloading, through a gap between the top end of the spiral wrap  156  of the fixed scroll  150  and the end plate  164  of the movable scroll  160  and a gap between the top end of the spiral wrap  166  of the movable scroll  160  and the end plate  154  of the fixed scroll  150 , thereby providing an axial flexibility for the scroll compressor. 
     On the other hand, in order to achieve a radial seal between a side surface of the spiral wrap  156  of the fixed scroll  150  and a side surface of the spiral wrap  166  of the movable scroll  160 , and in order to maintain such radial seal between them at a suitable value both in a high rotational speed condition and in a low rotational speed condition, a movable scroll counterweight  40  is further provided in the scroll compressor  10  according to the first embodiment of the application. The movable scroll counterweight  40  is configured to rotate with the driving shaft  30  and generate the centrifugal force due to the rotation to act on the hub portion  162  of the movable scroll  160 . 
     Preferably, the direction of the centrifugal force of the movable scroll counterweight  40  can be set to substantially be opposite to the direction of the centrifugal force of the movable scroll  160 . Accordingly, the movable scroll counterweight can most effectively counteract the centrifugal force of the movable scroll  160 . Further, the centrifugal force of the movable scroll counterweight  40  may be set to be approximately equal to the centrifugal force of the movable scroll  160 . In this case, the centrifugal force of the movable scroll  160  can completely be counteracted by the movable scroll counterweight  40 . However, the skilled person in the art should understand that the centrifugal force of the movable scroll counterweight  40  may also be set to be different from the centrifugal force of the movable scroll  160 . In this case, the centrifugal force of the movable scroll  160  will at least partially counteracted by the centrifugal force of the movable scroll counterweight  40 . Therefore, the difference between the radial sealing force between the scroll components under the high rotational speed condition and under the rotational low speed condition can also be reduced, thereby avoiding an improper sealing under the low rotational speed condition and an excessive wear under the high rotational speed condition. 
     Specifically, as shown in  FIGS. 3, 7A and 7B , the movable scroll counterweight  40  may include a cylindrical portion  42  disposed to surround the hub portion  162  of the movable scroll  160 . A bearing  46  is provided in the cylindrical portion  42  of the movable scroll counterweight  40 , and an inner side of the bearing  46  contacts an outer side of the hub portion  162 . The bearing  46  may be a rolling bearing or a sliding bearing or any other suitable bearing. The bearing  46  contributes to the transmission of force between the movable scroll counterweight  40  and the hub portion  162  of the movable scroll  160  and contributes to reducing wears therebetween. However, those skilled in the art will understand that the bearing  46  may also be omitted as a modification shown in  FIGS. 14, 15A and 15B . Then, the movable scroll counterweight  40  may be provided such that at least a portion of its cylindrical portion  42  contacts the outer side of the hub portion  162 . 
     As shown in  FIGS. 4, 6A, 6B and 6C , a driving portion  33  may be provided on an outer peripheral surface of the driving shaft  30  for driving the movable scroll counterweight  40  to rotate. As shown in  FIGS. 7A and 7B , the movable scroll counterweight  40  may include a bottom wall  44 , and a driving hole  48  fitted with the driving portion  33  may be provided on the bottom wall  44 . The shape of the driving portion  33  may be set to substantially correspond to the shape of the driving hole  48 . Irrespective of providing a radial flexibility for the compressor, the driving portion  33  may have any non-circular cross-section for driving the movable scroll counterweight  40 . In practice, the driving portion  33  and the driving hole  48  may be of any construction that allows them to be fitted with each another so as to perform the transmission of power. 
     In consideration of providing a radial flexibility for the compressor, the maximum size of the driving portion  33  in the radial direction may be set to be equal to or less than the maximum size of the driving hole  48  in the radial direction. Further, the driving portion  33  and the driving hole  48  may be configured such as to allow the movable scroll counterweight  40  to slide on the driving portion  33  in the radial direction. 
     More specifically, as shown in  FIGS. 6A, 6B and 6C , the driving portion  33  may include two step portions  34  and  35 . The step portions  34 ,  35  include respective bottom surfaces  341 ,  351  and respective side surfaces  342 ,  352 . The side surfaces  342 ,  352  of the two step portions  34 ,  35  are parallel to each other. As shown in  FIGS. 7A and 7B , a driving hole  48  is formed in the bottom wall  44  of the movable scroll counterweight  40 , and has two side walls  481 ,  482  fitted with the side surfaces  342 ,  352  of the two step portions  34 ,  35 . The driving hole  48  also has two arc side walls  483 ,  484  respectively connected to the two side walls  481 ,  482 . Preferably, the two side walls  481 ,  482  of the driving hole  48  are provided in parallel to each other. 
     The respective side surfaces  342 ,  352  of the step portions  34 ,  35  may be configured to be substantially parallel to the direction of the centrifugal force of the movable scroll  160 . A distance between the side surfaces  342 ,  352  of the two step portions  34 ,  35  may be set to be approximately equal to a distance between the two side walls  481 ,  482  of the driving hole  48  of the movable scroll counterweight  40 . The movable scroll counterweight  40  is supported in the axial direction by the bottom surface  341 ,  351  of at least one of the step portions  34 ,  35  of the driving shaft  30 . 
     Further, as shown in  FIG. 11 , a gap between the eccentric crank pin  32  and the unloading bushing  60  in the radial direction parallel to the planar portion  321  of the eccentric crank pin  32  is indicated as C1, and a gap between the driving shaft  30  and the driving hole  48  of the movable scroll counterweight  40  in the radial direction parallel to the side walls  481 ,  482  of the driving hole  48  is indicated as C2. Then, the relationship between C1 and C2 may be set as C2≧C1. It will be appreciated by those skilled in the art that the gap C1 is a total gap between the eccentric crank pin  32  and the unloading bushing  60  in the radial direction, and the gap C2 is a total gap between the driving shaft  30  and the driving hole  48  of the movable scroll counterweight  40  in the radial direction. 
     With the above construction, when the driving shaft  30  drives the movable scroll  160  to rotate, the movable scroll counterweight  40  rotates synchronously with the movable scroll  160  by means of the cooperation between the driving hole  48  and the step portions  34 ,  35 . The centrifugal force generated by the movable scroll counterweight  40  will be transmitted to the hub portion  162  of the movable scroll  160  via the cylindrical portion  42  and the bearing  46 . Since the movable scroll counterweight  40  is assembled such that the direction of its centrifugal force is substantially opposite to the direction of the centrifugal force of the movable scroll  160 , the centrifugal force of the movable scroll counterweight  40  can counteract at least a portion of the centrifugal force of the movable scroll  160 . In particular, when the centrifugal force of the movable scroll counterweight  40  is set to be substantially equal to the centrifugal force of the movable scroll  160 , the centrifugal force of the movable scroll  160  will be counteracted completely. In this case, whether the rotational speed of the driving shaft  30  is high or low, the radial sealing force between the movable scroll and the fixed scroll is independent of the centrifugal force of the movable scroll  160 . 
     Referring to  FIG. 12 , specifically, a total radial sealing force between the fixed scroll  150  and the movable scroll  160  of the scroll compressor  10  according to the first embodiment of the present application may be represented by the formula:
 
 F   flank   =F   IOS   +F   s  Sin θ eff   −F   IO *Sin θ− F   rg   −F   IU   formula (2)
 
Where
 
F flank  is a total radial sealing force between the fixed scroll  150  and the movable scroll  160 ;
 
F IOS  is the centrifugal force of the movable scroll  160 ;
 
F s  Sin θ eff  is a component of the driving force provided by the eccentric crank pin  32 , wherein F s  is the total driving force provided by the eccentric crank pin  32 , and θ eff  is the effective driving angle of the eccentric crank pin  32 ;
 
F IO *Sin θ is a component of the centrifugal force provided by the Oldham coupling  190 , wherein F IO  is the total centrifugal force provided by the Oldham coupling  190 , and θ is a angle of the movable scroll  160  oriented relative to the fixed scroll  150 ;
 
F rg  is a gas force provided by the fluid in the compression pockets; and
 
F IU  is the centrifugal force of the movable scroll counterweight  40 .
 
     As can be seen from the above formula 2, while F IOS  and F IU  are items relating to the rotational speed of the driving shaft, by setting F IU  to be substantially equal to F IOS , the difference (F IOS −F IU ) between F IOS  and F IU  is substantially zero. In particular, regardless of the rotational speed of the driving shaft, the difference (F IOS −F IU ) between F IOS  and F IU  is substantially zero. Thus, the above formula 2 can be simplified as the following formula 3:
 
 F   flank   =F   s  Sin θ eff   −F   IO *Sin θ− F   rg   formula (3)
 
     In the formula 3, only F IO *Sin θ is an item relating to the rotational speed of the driving shaft  130 . However, due to the weight of the Oldham coupling  190  is very small, this item may be negligible. F rg  is an item independent of the rotational speed of the driving shaft  130 , and may be considered as a constant. F s  Sin θ eff  is also an item independent of the rotational speed of the driving shaft  130 . In the case that the effective driving angle θ eff  is unchanged, it may be considered as a constant. However, the magnitude of this item can be varied by changing the effective driving angle θ eff  of the eccentric crank pin  32 . 
     Thus, in the scroll compressor  10  according to the first embodiment of the present application, a radial sealing force F flank  is a constant independent of the rotational speed of the driving shaft  130 . In other words, regardless of the rotational speed of the driving shaft  30 , a radial sealing force F flank  is constant. On the other hand, since the magnitude of F s  Sin θ eff  may be changed by changing the effective driving angle θ eff  of the eccentric crank pin  32 , a desired radial sealing force may be adjusted by adjusting the effective driving angle θ eff . Thus, whether the scroll compressor  10  is in a low rotational speed condition or in a high rotational speed condition, a suitable radial sealing force can be achieved. It is possible to avoid efficiency of the compressor from being reduced due to the insufficient radial sealing force, and also to avoid the scroll components from excessive wear due to the excessive radial sealing force. 
     In addition, as described above, the gap C2 between the driving shaft  30  and the driving hole  48  of the movable scroll counterweight  40  in the radial direction is set to be equal to or greater than the gap C1 between the eccentric crank pin  32  and the unloading bushing  60  in a radial direction. As a result, the scroll compressor  10  according to the embodiments of the present application still has a radial flexibility. 
     Specifically, when uncompressible materials (such as solid impurities, lubricating oil and liquid refrigerant) enter the compression pockets and get stuck between the spiral wrap  156  and the spiral wrap  166 , the movable scroll  160  may be displaced by C1 maximally in the radial direction due to the gap C1 between the eccentric crank pin  32  and the unloading bushing  60 . Then, the foreign matters are allowed to pass between the spiral wrap  156  and the spiral wrap  166  radially spaced apart from one another. Meanwhile, since the cylindrical portion  42  of the movable scroll counterweight  40  is disposed at the outer periphery of the hub portion  162  of the movable scroll  160 , when the movable scroll  160  is radially displaced, it may drive the movable scroll counterweight  40  to radially displace. In this case, since the gap C2 between the driving holes  48  of the movable scroll counterweight  40  and the driving shaft  30  is equal to or greater than the gap C1, the radial displacement of the movable scroll counterweight  40  may be free from the driving shaft  30 . Therefore, the movable scroll  160  and the movable scroll counter weight  40  both may displace by a maximum distance of C1. Thus, a constant radial sealing force can be provided for the scroll compressor, and a radial flexibility can be still provided for the scroll compressor. 
     It will be understood by those skilled in the art that, in the case that a radial flexibility is not required for the scroll compressor, the unloading bushing  60  can be omitted, and the gap C2 need not be provided. In particular, the cooperation between the driving shaft and the movable scroll counterweight may be achieved by any structure that can cause the driving shaft to drive the movable scroll counterweight to rotate, which is not limited to the structure shown in  FIGS. 6 and 7 . For example, a D-shaped section may be provided on the driving shaft  30 , and accordingly, the movable scroll counterweight  40  may have a matched D-shaped hole. 
     It will also be understood by those skilled in the art that, an example of the driving connection between the driving shaft  30  and the movable scroll counterweight  40  is given with reference to  FIGS. 6 and 7  above, but the application is not limited thereto. In contrast, in view of providing a radial flexibility for the compressor, the driving portion  33  and the driving hole  48  may be configured to be of any configuration that enables a radial slide of the movable scroll counterweight  40  relative to the driving shaft  30 . For example, a key may be provided on the driving shaft  30 , and a key slot is provided in the driving hole  48 , with the radial size of the driving hole  48  being set to be greater than the radial size of the driving shaft  30  such that the key of the driving shaft  30  can be fitted in the key slot of the driving hole  48  so as to drive the movable scroll counterweight to rotate while allowing the movable scroll counterweight to radially slide relative to the driving shaft along the key. As another example, the movable scroll counterweight  40  may include a hub portion downwardly extending to surround the driving shaft  30  and having an inner diameter larger than the outer diameter of the driving shaft, and a hole may be provided on each of the hub portion and the driving shaft, so that one pin may pass through the hole in the hub portion and then be fixed in the hole of the driving shaft. In this configuration, the driving shaft may also drive the movable scroll counterweight to rotate and allow the movable scroll counterweight to radially slide along the pin relative to the driving shaft. Based on the principle of the application, many other configurations can be readily contemplated by those skilled in the art, and will not be enumerated herein. 
     A relationship of the mass and orbiting radius between the movable scroll and the movable scroll counterweight will be described with reference to  FIG. 13  below. As shown in  FIG. 13 , the center M2 of gravity of the movable scroll counterweight  40  and the center M1 of gravity of the movable scroll  160  are on opposite sides of the rotational axis O of the driving shaft  30 . Assuming that the mass of the movable scroll  160  is M1 and the minimum orbiting radius of the movable scroll  160  is D1; and assuming that the mass of the movable scroll counterweight  40  is M2 and the maximum orbiting radius of the centroid of the movable scroll counterweight  40  is D2, the above parameters may be set to satisfy formula 4: M1*D1≧M2*D2. Further, it is assumed that a distance between the center of gravity of the movable scroll  160  and the rotational axis of the driving shaft  30  during a normal operation of the scroll compressor  10  is d1, then D1=d1−C1; and it is assumed that a distance between the center of gravity of the movable scroll counterweight  40  and the rotational axis of the driving shaft  30  during a normal operation of the scroll compressor  10  is d2, then D2=d2+C1. The “normal operation” means that the movable scroll of the scroll compressor moves without radial displacement (i.e. performing a radial flexibility). 
     From the above formulas, the mass and its orbiting radius of the movable scroll counterweight  40  can easily be set, and it is ensured that the movable scroll  160  can be securely engaged with the fixed scroll  150  in any case (including the case that a radial flexibility is performed). 
     Seeing  FIGS. 16-20 , the scroll compressor according to the second embodiment of the present application will be described below. This embodiment differs from the first embodiment in the cooperating and connection relationships between the movable scroll counterweight and the driving shaft as well as the hub portion of the movable scroll. 
     Specifically, a mated hole  36  may be provided in the outer peripheral surface of the driving shaft  30 , and a driving hole  49  may also be formed in the bottom wall of the movable scroll counterweight  40 . The movable scroll counterweight  40  and the driving shaft  30  may be connected to each other by a driving rod  70 . A first end  72  of the driving rod  70  may be fitted in the mated hole  36  of the driving shaft  30 , and a second end  74  of the driving rod  70  may be fitted in the driving hole  49  of the movable scroll counterweight  40 . The cylindrical portion  42  of the movable scroll counterweight  40  is disposed to surround the hub portion  162  of the movable scroll  160 . A snap spring  80  may be provided at the outer side of the hub portion  162  of the movable scroll  160  to axially hold the movable scroll counterweight  40 . Thus, as the driving shaft  30  rotates, the driving shaft  30  drives the driving rod  70 , which, in turn, drives the movable scroll counterweight  40  to rotate by the driving hole  49 . 
     As shown in  FIGS. 17A and 17B , a bearing  46  may be provided in the cylindrical portion  42 , but the bearing  46  may also be omitted as variations shown in  FIGS. 21A and 21B . 
     The driving rod  70  may be substantially L-shaped. However, those skilled in the art will understand that, the driving rod  70  may have any other suitable shape adapted to drive the movable scroll counterweight. 
     To achieve a radial flexibility of the scroll compressor, the driving hole  49  may be an elongated hole substantially extending in the radial direction of the movable scroll counterweight  40 . 
     In this case, it is assumed that a gap between the eccentric crank pin  32  and the unloading bushing  60  in a radial direction parallel to the planar portion  321  of the eccentric crank pin  32  is C1, and it is assumed that the radial length of the elongated hole is C3, then the relationship between C1 and C3 may be set as C3≧C1. 
     Further, in the present embodiment, the relationship of the mass and orbiting radius between the movable scroll and the movable scroll counterweight can still be set to satisfy the above formula 4. 
     A lubricant supply structure of the movable scroll counterweight  40  will be described further with respect to  FIGS. 7A and 7B  below. More specifically, at least one oil supply groove  410  or  411  may be disposed on the inner circumference of the cylindrical portion  42  of the movable scroll counterweight  40 . The oil supply grooves  410  and  411  may extend substantially in the axial direction of the scroll compressor. However, those skilled in the art will understand that, the oil supply grooves  410  and  411  may also extend in such a manner as being inclined relative to the axial direction of the scroll compressor. In  FIGS. 7A and 7B , a pair of oil supply grooves  410 ,  411  are provided, for example, being substantially symmetric with respect to the rotational center of the movable scroll counterweight  40 . Although the oil supply groove  410  is shown in  FIGS. 7A and 7B  to be disposed on one side of the cylindrical portion  42  close to a thickening portion  49 , and the oil supply groove  411  is shown to be disposed on the other side of the cylindrical portion  42  opposite to the thickening portion  49 , it will be understood by those skilled in the art that, the number and position of the oil supply groove can be set as desired. For example, in the example shown in  FIG. 11 , the oil supply grooves  410  and  411  may be provided on opposite sides of the thickening portion  49 . The oil supply grooves  410  and  411  may extend to the bottom wall  44  of the movable scroll counterweight  40  in an axial direction. 
     A lubrication system of the scroll compressor  10  will be described with reference to  FIGS. 3 and 22  below. As shown in  FIG. 3 , the driving shaft  30  includes a central hole  37  substantially centrally located in the lower end thereof and an eccentric hole  38  extending upwardly to an end face of the eccentric crank pin  32  in the axial direction of the driving shaft  30  from the central hole  37 . Lubricant at a bottom portion of the housing of the compressor is supplied into the central hole  37 , for example, by a lubricant supply device such as a pump and moves further upwardly along the eccentric hole  38  under the centrifugal force induced through the rotation of the driving shaft  30 , and finally is discharged from an end portion of the eccentric crank pin  32 . Lubricant discharged from the eccentric crank pin  32  flows as indicated by arrows A and B. More specifically, a portion of lubricant indicated by the arrow A moves along the bottom wall  44  towards the radial outer side of the movable scroll counterweight  40  to a lower end of the oil supply grooves  410  and  411  under the action of centrifugal force. Then, the lubricant moves upwardly along the oil supply grooves  410  and  411  and, under the action of inertia, reaches thrust surfaces between the movable scroll end plate  164  and the thrust plate  50  for lubricating. In addition, in this process, the lubricant also lubricates the bearing  46  disposed on the inner side of the cylindrical portion  42 . On the other hand, a portion of lubricant indicated by the arrow B will move downwardly under the action of gravity and will be accumulated in a recess of the main bearing housing  20 . The lubricant accumulated in the recess of the main bearing housing  20  may continue to flow downwardly to pass through the main bearing  144  and, due to rotation of the driving shaft  30 , may splash to other moving components so as to achieve the lubrication. 
     For better lubricating the thrust surfaces between the movable scroll end plate  164  and the thrust plate  50 , for example, as shown in  FIGS. 14, 15A and 15B , the portion, in which the oil supply grooves  410  and  411  are provided, of the cylindrical portion  42  of the movable scroll counterweight  40  can be higher than the other portions of the cylindrical portion  42 , or may be configured to be adjacent to a lower surface of the movable scroll end plate  164 . Thus, the lubricant can flow along the oil supply grooves  410  and  411  to a position that is closer to the movable scroll end plate  164 , thereby achieving a better lubrication effect. 
     Further, referring to  FIGS. 7A and 7B , a step portion  412  protruding from the bottom wall  44  may also be formed on the bottom wall  44  of the movable scroll counterweight  40 . The oil supply grooves  410 ,  411  may extend axially to the step portion  412 . Although the step portion  412  is shown as a step portion that extends annularly in a circumferential direction in  FIGS. 7A and 7B , it will be understood by those skilled in the art that the step portion  412  may also be formed only in the vicinity of the lower end of the oil supply grooves  410 ,  411 . The height of the step portion  412  protruding relative to the bottom wall  44  may be set such that a ratio of the lubricant flowing upwardly through the oil supply grooves  410 ,  411  (the lubricant as designated by the arrow A in  FIG. 22 ) to the lubricant flowing downwardly through the driving hole  48  formed in the bottom wall  44  (the lubricant as designated by the arrow B in  FIG. 22 ) reaches a predetermined value. Thus, by designing the height of the step portion  412 , the amount of lubricant supplied to the various parts can be easily controlled, thereby achieving an optimization of the lubricating and working efficiency of the compressor. 
     Further, for example, the bottom wall  44  of the movable scroll counterweight  40  may be omitted, as shown in  FIGS. 17A, 17B  and  FIGS. 21A and 21B . In this case, since the lubricant may splash with the rotation of the driving shaft  30 , the oil supply grooves  410 ,  411  formed in the cylindrical portion  42  still contribute to supplying the lubricant to the thrust surfaces between the movable scroll end plate  164  and the thrust plate  50  and supplying the lubricant between the movable scroll counterweight  40  and the hub portion  162  of the movable scroll  160 . 
     Although various embodiments of the application have been described in detail herein, it should be understood that the application is not limited to the specific embodiments described and illustrated in detail herein. Without departing from the spirit and scope of the application, other modifications and variations can be implemented by the person skilled in the art. All such modifications and variations are within the scope of the present application. Moreover, all the members described herein may be replaced by other technically equivalent members.