WO2004038225A1

WO2004038225A1 - Compressor

Info

Publication number: WO2004038225A1
Application number: PCT/KR2003/001469
Authority: WO
Inventors: Kwang-Sik Yang; Chang-Ryul Kim
Original assignee: Lg Electronics Inc.
Priority date: 2002-10-25
Filing date: 2003-07-23
Publication date: 2004-05-06
Also published as: KR20040036973A; AU2003250560A1

Abstract

Disclosed is a compressor, in which a space portion having a predetermined volume is formed at a sliding part between a thrust bearing surface (T) of bearing plates (40, 50) and a supporting portion (22) of a rotational shaft where an axial load of the rotational shaft is supported, and a connection passage for connecting the space portion to outside of a cylinder assembly is formed. According to this, a surface pressure applied to the sliding part is reduced thus to reduce a frictional loss and abrasion of the components, thereby enhancing a performance of the compressor.

Description

COMPRESSOR

TECHNICAL FIELD

The present invention relates to a compressor, and more particularly, to a compressor which reduces a frictional loss by reducing a surface pressure of a sliding part in the compressor and thereby enhances efficiency thereof.

BACKGROUND ART

In general, a compressor is a device for converting mechanical energy into compression energy of compressible fluid, and is classified into a reciprocating compressor, a scroll compressor, a centrifugal compressor, a rotary compressor, and etc. by a compression method.

Among these compressors, the rotary compressor is a compressor for sucking, compressing, and discharging fluid by rotating a body of rotation and thus consecutively changing a suction region and a compression region under a state that a vane is inserted into the body of rotation and thus an inner space of a cylinder is divided into the suction region and the compression region.

Hereinafter, the rotary compressor will be explained.

Figure 1 is a longitudinal section view showing main parts of a compressor in accordance with the conventional art, and Figure 2 is a perspective view showing a compression unit of the conventional compressor by partially cutting.

As shown in Figures 1 and 2, the conventional compressor comprises: a hermetic container 10 to which a suction pipe 35 and a discharge pipe (not shown) are connected; a electronic driving unit 12 installed in the hermetic container 10 for generating a rotation force; and a compression unit 14 installed in the hermetic container 10 with a predetermined interval from the driving unit 12 for sucking, compressing, and discharging compressible fluid by the rotation force generated from the driving unit 12.

Like a general electric motor, the driving unit 12 is composed of a stator 16 closely fixed to an inner circumference surface of the hermetic container 10, and a rotor 18 installed to have a maintain a constant air gap from the inner circumference surface of the stator 16 for generating a rotation force by electromagnetic interaction with the stator 16.

The compression unit 14 comprises: a cylinder assembly 31 installed in the hermetic container 10 and forming a compression space V where compressible fluid sucked from outside is compressed; a rotational shaft 20 rotatably fixed to the cylinder assembly 31 and closely fixed to an inner circumference surface of the rotor 18 thus to be rotated together when the rotor 18 is rotated; a compression member 23 rotated by being engaged to the rotational shaft 20 and for dividing the compression space V in the cylinder assembly 31 into a first space V1 and a second space V2; and first and second vanes 60 and 70 respectively contacted on upper and lower surfaces of the compression member 23 and for dividing the first and second spaces V1 and V2 into suction regions Via, V2a and compression regions V1 b, V2b by being reciprocated towards inner and outer direction of the compression space V along the upper and lower surfaces of the compression member 23 when the compression member 23 is rotated.

The cylinder assembly 31 comprises: a cylinder 30 formed as a cylindrical shape and having a suction flow path 36 through which gas is sucked to the first and second spaces V1 and V2, the suction flow path 36 connected to the suction pipe 35; and first and second bearing plates 40 and 50 fixed to both sides of the cylinder 30 thus to form a compression space with the cylinder 30 and for supporting the rotational shaft 20.

The first and second bearing plates 40 and 50 are formed as a disc shape having a predetermined thickness and area, and comprises: journal portions 42 and 52 prolonged to have a predetermined height and an outer diameter, and having a penetrated center for rotatably inserting the rotational shaft 20; first and second vane slots 44 and 54 formed by penetrating the first and second bearing plates 40 and 50 for inserting the first and second vanes 60 and 70; discharge flow paths 46 and 56 formed at one side of the first and second vane slots 44 and 54 for discharging gas compressed in the compression space V of the cylinder assembly 31.

Also, a first discharge muffler 45 and a second discharge muffler 55 are respectively formed at upper and lower sides of the first and second bearing plates 40 and 50 by being covered.

The rotational shaft 20 comprises: a shaft portion 21 formed to have a predetermined outer diameter and a length and inserted into the journal portions 42 and 52 of the first and second bearing plates 40 and 50; a hub portion 22 integrally enlarged at a periphery of the shaft portion 21 thus to be supported on inner surfaces of the first and second bearing plates 40 and 50, and engaged to the compression member 23 in the cylinder assembly 31 ; an oil flow path 25 penetratingly formed inside the shaft portion 21 ; and an oil feeder 24 installed at a lower end of the rotational shaft 20 for supplying oil contained at a lower portion of the hermetic container 10 to an upper side. Here, the hub portion 22 of the rotational shaft 20 is concentric with the shaft portion 21 of the rotational shaft 20.

Also, as shown in Figure 3, a radial load of the rotational shaft 20 is supported on a radial bearing surface R of the journal portions 42 and 52 of the first and second bearing plates 40 and 50, and an axial load of the rotational shaft 20 is supported on a thrust bearing surface T of the inner surfaces of the first and second bearing plates 40 and 50.

The compression member 23 is formed as a disc shape in a plane view so that an outer circumference surface thereof can have a sliding contact with an inner circumference surface of the cylinder 30, and formed as a cam surface of sine wave having the same thickness from the inner circumference surface to the outer circumference surface in a lateral projection view. According to this, a side having an upper dead point D1 of the compression member 23 slidably contacts with a lower surface of the first bearing plate 40, and a side having a lower dead point D2 slidably contacts with an upper surface of the second bearing plate 50.

The first and second vanes 60 and 70 are formed as a rectangular plate shape and respectively adhere to an upper and lower surface of the compression member 23 in the compression space V of the cylinder assembly 31. The vanes 60 and 70 reciprocate up and down along a height of the cam surface of the compression member 23 when the compression member 23 is rotated, and thus divide the compression spaces V1 and V2 into the suction regions Via, V2a and the compression regions V1 b, V2b. Also, the first and second vanes 60 and 70 are elastically supported by an elastic supporting member 90 mounted at the first and second bearing plates 40 and 50.

Processes that the conventional compressor is operated will be explained as follows.

First, if the rotational shaft 20 is rotated by a driving force of the driving unit 12, the compression member 23 engaged to the rotational shaft 20 is simultaneously rotated in the cylinder assembly 31.

At this time, the first space V1 located at an upper portion of the compression member 23 is divided into the suction region Via and the compression region V1 b on the basis of the upper dead point D1 of the compression member 23 and the first vane 60. Also, the second space V2 located at a lower portion of the compression member 23 is divided into the suction region V2a and the compression region V2b on the basis of the lower dead point D2 and the second vane 70.

Under this state, capacities of the suction regions Via, V2a and the compression regions V1 b, V2b of the first and second spaces V1 and V2 are varied as the upper dead point D1 and the lower dead point D2 of the compression member 23 move by rotation of the compression member 23. At this time, the first and second vanes 60 and 70 reciprocate towards different directions on the basis of the compression member 23.

Accordingly, when the upper dead point D1 or the lower dead point D2 of the compression member 23 reaches to a discharge starting point after compressible fluid is sucked into the suction regions Via and V2a of the first and second spaces V1 and V2 through the suction flow path 36 and compressed, the fluid compressed is discharged outside the cylinder assembly 31 through the discharge flow paths 46 and 56 of the compression spaces V1 and V2. Then, the fluid discharged outside the cylinder assembly 31 passes through the first and second discharge mufflers 45 and 55 and inside of the hermetic container 10, and is discharged outside the hermetic container 10 through the discharge pipe (not shown).

At this time, as the rotational shaft 20 is rotated, oil contained in the lower portion of the hermetic container 10 is sucked by an oil feeder 24 mounted at a lower end of the rotational shaft 20 through the oil flow path 25, and dispersed at an upper end portion of the rotational shaft 20, thereby being supplied to sliding components in the compressor.

In the conventional compressor, the most influential factor to a performance of the compressor is a friction loss generating in a sliding part in the

cylinder assembly 31.

The friction is generated at the sliding part between the vanes 60, 70 and the compression member 23, between the vanes 60, 70 and the vane slots 44, 54, between the compression member 23 and the bearing plates 40, 50, and between the rotational shaft 20 and the bearing plates 40, 50. The friction causes noise of the com6pressor and abrasion of elements inside the compressor, thereby degrading performance and life span of the compressor. Also, by the friction of the sliding part, heat is generated thus to cause heat loss of refrigerant gas.

Especially, as shown in Figure 4, a supporting portion 22 for supporting the axial load of the rotational shaft 20 on the bearing plates 40, 50 and the thrust bearing surface T of the bearing plates 40, 50 rotate by being adhered as a radial width L of the supporting portion 22, so that great surface pressure is applied to the sliding part between the supporting portion 22 and the thrust bearing surface T. By the surface pressure, friction and abrasion are generated, so that the performance of the compressor is lowered and damage of the components is generated.

DISCLOSURE OF THE INVENTION

Therefore, it is an object of the present invention to provide a compressor which reduces a surface pressure generated at a sliding part and thus prevents friction loss and abrasion of components by forming a space portion having a predetermined volume at the sliding part between a supporting portion of a rotational shaft and a bearing plate, and by forming a connection passage for connecting outside of a cylinder assembly and the space portion in order to introduce discharged gas in a hermetic container into the space portion. To achieve these objects, there is provided a compressor comprising: a cylinder fixed in a hermetic container and for forming a compression space; a compression member arranged in the compression space of the cylinder thus to be rotated and for sucking, compressing, and discharging fluid by varying a capacity of the compression space; a rotational shaft fixed by a driving force generating means and for transmitting a rotation force generated from the driving force generating means to the compression member; and bearing plates for supporting an axial load and a radial load of the rotational shaft, wherein, a space portion having predetermined volume is formed at a sliding part between the rotational shaft and the bearing plate where the axial load of the rotational shaft is supported, and a connection passage for connecting outside of the cylinder to the space portion in order to introduce discharged gas outside the cylinder into the space portion is formed.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a longitudinal section view showing main parts of a compressor in accordance with the conventional art;

Figure 2 is a perspective view showing the conventional compressor by

partially cutting; Figure 3 is a partial section view showing a compression unit of the conventional compressor by disassembling;

Figure 4 is a partial section view showing a part where a surface pressure is applied between a bearing plate and a rotational shaft of the conventional compressor;

Figure 5 is a perspective view showing a compression unit of a

compressor according to one embodiment of the present invention by partially cutting; Figure 6 is a partial section view showing the compression unit of the compressor according to one embodiment of the present invention by disassembling;

Figure 7 is a plane view showing an inner surface of a bearing plate of the compressor according to one embodiment of the present invention; Figure 8 is a plane view showing an inner surface of a bearing plate of the compressor according to one embodiment of the present invention;

Figure 9 is a section view showing a part where a surface pressure is applied between the bearing plate and a rotational shaft of the compressor according to one embodiment of the present invention; Figure 10 is a longitudinal section view showing a compressor according to another embodiment of the present invention; and

Figure 11 is a longitudinal section view showing a compressor according to still another embodiment of the present invention.

MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of a compressor according to the present invention will be explained with reference to attached drawings.

Figure 5 is a perspective view showing a compression unit of a compressor according to one embodiment of the present invention by partially cutting, and Figure 6 is a partial section view showing the compression unit of the compressor according to one embodiment of the present invention by disassembling. The compressor according to one embodiment of the present invention comprises: a hermetic container to which a suction pipe and a discharge pipe are connected; a driving force generating means arranged in the hermetic container for generating a rotation force; and a compression unit 14 arranged in the hermetic container for sucking, compressing, and discharging compressible fluid by the driving force generated from the driving force generating means. In the compressor, fluid is sucked into the compression unit 14, compressed, and discharged in the hermetic container. The fluid is discharged outside the hermetic container through the discharge pipe engaged to the hermetic container. Accordingly, if the compressor is operated, a predetermined pressure is always applied in the hermetic container by discharged gas.

The compression unit 14 comprises: a cylinder assembly 31 installed in the hermetic container and forming compression spaces V1 and V2 therein; a rotational shaft 20 connected to the driving force generating means thus for transmitting a driving force; a compression member 23 arranged in the cylinder assembly 31 by being fixed to a circumference of the rotational shaft 20 and having a cam surface of a predetermined curvature so that capacities of the compression spaces V1 and V2 can be changed at the time of rotation; and first

and second vanes 60 and 70 respectively for dividing the first and second spaces V1 and V2 into suction regions and compression regions by being reciprocated toward inner and outer direction of the cylinder assembly 31 along the cam surface of the compression member 23 when the compression member 23 is rotated. The cylinder assembly 31 comprises: a cylinder 30 formed as a cylindrical shape; and first and second bearing plates 40 and 50 fixed to both sides of the cylinder 30 thus to form a compression space with the cylinder 30.

The first and second bearing plates 40 and 50 are formed as a disc shape having a predetermined thickness and area, and comprises: journal portions 42 and 52 prolonged to have a predetermined height and an outer diameter and having a penetrated center for rotatably inserting the rotational shaft 20; and first and second vane slots 54 formed at one side of the journal portions 42 and 52 for slidably inserting the first and second vanes 60 and 70.

The rotational shaft 20 formed to have a predetermined outer diameter and a length comprises: a shaft portion 21 inserted into the journal portions 42 and 52 of the first and second bearing plates 60 and 70 and for supporting a radial load of the rotational shaft 20 on the journal portions 42 and 52 of the first and second bearings 60 and 70; and a supporting portion 22 integrally enlarged at a periphery of the shaft portion 21 thus for supporting an axial load of the rotational shaft 20 on inner surfaces of the first and second bearing plates 40 and 50, and engaged to the compression member 23 in the cylinder assembly 31. Here, the supporting portion 22 of the rotational shaft 20 is formed to be concentric with the shaft portion 21 of the rotational shaft 20 in a plane view. Accordingly, the radial load of the rotational shaft 20 is supported on a radial bearing surface R in the journal portions 42 and 52 of the first and second bearing plates 40 and 50, and the axial load of the rotational shaft 20 is supported on a thrust bearing surface T of the inner surfaces of the first and second bearing plates 40 and 50.

Herein, a space portion 48 and 58 having a predetermined width and depth is formed at the thrust bearing surface T of the first and second bearing plates 40 and 50 in order to reduce a surface pressure between the thrust bearing surface T and the supporting portion 22 of the rotational shaft 20. Also, connection passages 49 and 59 for introducing discharged gas outside the cylinder assembly 31 into the space portions 48 and 58 and introducing lubrication oil outside the cylinder assembly 31 into the space portions 48 and 58 are respectively formed by penetrating the first and second bearing plates 40 and 50. That is, a part of the discharged gas outside the cylinder assembly 31 is introduced into the space portions 48 and 58 through the connection passages 49 and 59, so that a predetermined pressure is applied to the space portions 48 and 58. Also, since the pressure is applied in the opposite direction to that of the surface pressure applied to the thrust bearing surface T and the supporting portion 22, a size of the surface pressure applied to the thrust bearing surface T and the supporting portion 22 can be reduced.

Also, lubrication oil which is outside the cylinder assembly 31 is introduced into the space portions 48 and 58 through the connection passages 49 and 59, and the introduced oil is supplied to a sliding part between the thrust bearing surface T and the supporting portion 22, so that friction of the sliding part between the thrust bearing surface T and the supporting portion 22 can be reduced. Therefore, as the surface pressure generated at the sliding part between the thrust bearing surface T and the supporting portion 22 is reduced and oil performs the lubrication operation, friction of the sliding part is reduced thus to reduce a frictional loss of the compressor and to reduce abrasion of the components in the compressor, thereby greatly enhancing a performance of the compressor.

In the meantime, as shown in Figure 7, the space portions 48 and 58 can be formed as a ring shape in a plane view, or as shown in Figure 8, the space portions 48 and 58 can be formed as a circular arc shape. Also, the space portions 48 and 58 are not limited to said ring shape or the circular arc shape, but can be formed as various shapes. In case that the space portions 48 and 58 are plural, it is preferable that the plurality of the space portions are formed with the same interval without being eccentric from the center of the rotational shaft 20, and it is preferable that they are formed symmetrically on the basis of the radial direction of the rotational shaft 20. Meanwhile, the connection passages 49 and 59 are preferably formed at the first and second bearing plates 40 and 50 by penetrating towards the shaft

direction, and areas thereof are smaller than horizontal areas of the space portions 48 and 58. Also, a processing is easy when sectional areas of the connection passages 49 and 59 are equally formed from outside of the first and second plates 40 and 50 to the space portions 48 and 58. However, the sectional areas of the connection passages can be increased towards the space portions 48 and 58 in order to smoothly introduce discharged gas and oil outside the cylinder assembly 31 into the space portions 48 and 58.

The compression member 23 is formed as a disc shape in a plane view so that an outer circumference surface thereof can have a sliding contact with an inner circumference surface of the cylinder 30, and formed as a cam shape of sine wave having the same thickness from the inner circumference surface to the outer circumference surface in a lateral projection view. According to this, a side having an upper dead point slidably contacts with a lower surface of the first bearing plate 40, and a side having a lower dead point slidably contacts with an upper surface of the second bearing plate 50.

The first and second vanes 60 and 70 are formed as a rectangular plate shape and adhere to the cam surface of the compression member 23 in the compression space of the cylinder assembly 31. The vanes reciprocate up and down along a height of the cam surface of the compression member 23 when the compression member 23 is rotated, and thus divide the compression spaces V1 and V2 into suction regions and compression regions. Operations and effects of the compressor according to the first embodiment of the present invention will be explained as follows.

First, if the rotational shaft 20 is rotated by a driving force of the driving force generating means, the compression member 23 engaged to the supporting portion 22 of the rotational shaft 20 is simultaneously rotated in the cylinder assembly 31.

At this time, the first space V1 located at an upper portion of the compression member 23 is divided into the suction region and the compression region on the basis of the upper dead point of the compression member 23 and the first vane 60. Also, the second space V2 located at a lower portion of the compression member 23 is divided into the suction region and the compression region on the basis of the lower dead point and the second vane 70.

Under this state, capacities of the suction regions and the compression regions of the first and second spaces V1 and V2 are varied as the upper dead point and the lower dead point of the compression member 23 move by rotation of the compression member 23.

At this time, the first and second vanes 60 and 70 reciprocate towards different directions along the height of the cam surface of the compression member 23.

Accordingly, when the upper dead point or the lower dead point of the compression member 23 reaches to a discharge starting point after compressible fluid is sucked into the suction regions of the first and second spaces V1 and V2 and compressed, the fluid compressed is discharged outside the cylinder assembly 31 through the discharge flow paths of the compression spaces V1 and V2.

Also, the fluid discharged outside the cylinder assembly 31 passes inside of the hermetic container and is discharged outside the hermetic container through the discharge pipe.

At this time, as the rotational shaft 20 is rotated, oil contained in the lower portion of the hermetic container is sucked by an oil feeder mounted at a lower end of an oil flow path of the rotational shaft 20, and dispersed at an upper end portion of the rotational shaft 20, thereby being supplied to sliding components in the compressor.

Also, the rotational shaft 20 rotates by being inserted into the journal portions 42 and 52 of the first and second bearing plates 40 and 50. At this time, the shaft portion 21 of the rotational shaft 20 is rotated by being supported on the radial bearing surface R of the first and second bearing plates 40 and 50, and both sides of the supporting portion 22 of the rotational shaft 20 are rotated by being supported on the thrust bearing surface T of the first and second bearing plates 40 and 50. Also, a predetermined surface pressure is applied to said both sides of the supporting portion 22 of the rotational shaft 20 which is opposite to the area of the thrust bearing surface T.

At this time, as shown in Figure 9, by forming the space portions 48 and 58 at the thrust bearing surface T of the first and second bearing plates 40 and 50, a width of the sliding part between the thrust bearing surface T and the supporting portion 22 is decreased. That is, amount corresponding to the width L1 of the space portions 48 and 58 is decreased from the width L of the supporting portion 22, thereby reducing a friction area of the thrust bearing surface T. Also, a part of the discharge gas discharged into the hermetic container is introduced into the space portions 48 and 58 through the connection passages 49 and 59 which respectively connect the space portions 48 and 58 and the outside of the cylinder assembly 31 , so that a predetermined pressure is formed in the space portions 48 and 58. By the pressure of the space portions 48 and 58, the surface pressure generated between the thrust bearing surface T and the supporting portion 22 is decreased. Accordingly, frictional loss generated between the thrust bearing surface T and the supporting portion 22 is reduced thus to enhance efficiency of the compressor.

Also, lubrication oil which is outside the cylinder assembly 31 is introduced into the space portions 48 and 58 through the connection passages 49 and 59, and then supplied between the thrust bearing surface T of the first and second bearing plates 40 and 50 and the supporting portion 22 of the rotational shaft 20 thus to perform lubrication operation. According to this, friction of the thrust bearing surface T is reduced thus to enhance efficiency of the compressor. Hereinafter, another embodiment of the present invention will be explained with reference to Figure 10. The same parts as those of the first embodiment of the present invention will have the same reference numerals, and their explanations will be omitted.

Figure 10 is a longitudinal section view showing a compressor according to another embodiment of the present invention.

Whereas the space portions 48 and 58 which reduce the surface pressure are formed at the thrust bearing surface T of the first and second

bearing plates 40 and 50 in the compressor according to the first embodiment of the present invention, a space portion 120 which reduces the surface pressure is formed at the supporting portion 22 of the rotational shaft 20 which is opposite to the thrust bearing surface T of the first and second bearing plates 40 and 50 in the compressor according to another embodiment of the present invention. Also, connection passages 149 and 159 is formed by penetrating the first and second bearing plates 40 and 50 in order to connect the space portion 120 of the supporting portion 22 to the outside of the cylinder assembly 31.

In the meantime, operations and effects of the compressor according to another embodiment of the present invention are same as those of the compressor according to the first embodiment.

Hereinafter, still another embodiment of the present invention will be explained with reference to Figure 11. The same parts as those of the aforementioned embodiments of the present invention will have the same reference numerals, and their explanations will be omitted. Figure 11 is a longitudinal section view showing a compressor according to still another embodiment of the present invention. In the compressor according to still another embodiment of the present invention, first space portions 248 and 258 are formed at the thrust bearing surface T in order to reduce the surface pressure generated between the thrust bearing surface T of the first and second bearing plates 40 and 50 and the supporting portion 22 of the rotational shaft 20, and a second space portion 220 is formed at the supporting portion 22 of the rotational shaft 20.

Also, connection passages 249 and 259 are formed by penetrating the first and second bearing plates 40 and 50 in order to connect the first space portions 248 and 258 and the second space portion 220 to the outside of the cylinder assembly 31.

That is, in the compressor according to the first and another embodiment of the present invention, thickness of the first and second bearing plates 40 and 50 or thickness of the supporting portion 22 of the rotational shaft 20 was considered when the space portions 48, 58, and 120 are formed. However, in the compressor according to still another embodiment of the present invention, the first space portions 248 and 258 and the second space portion 220 which reduce the surface pressure are respectively formed at the supporting portion 22 of the rotational shaft 20, so that volumes of the first and second space portions 248, 258, and 220 can be increased.

Operations and effects of the compressor according to still another embodiment of the present invention are same as those of the aforementioned embodiments.

In the compressor according to the present invention, the space portions having a predetermined volume are formed at the sliding part between the thrust bearing surface and the supporting portion of the bearing plates where the axial load of the rotational shaft is rotatably supported, and the connection passage for connecting the space portions to the outside of the cylinder assembly is provided. According to this, the surface pressure applied to the sliding part is reduced thus to reduce the frictional loss and abrasion of the components, thereby enhancing a performance of the compressor. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

1. A compressor comprising:

a cylinder fixed in a hermetic container and for forming a compression space; a compression member arranged in the compression space of the cylinder thus to be rotated and for sucking, compressing, and discharging fluid by varying a capacity of the compression space; a rotational shaft fixed by a driving force generating means and for transmitting a rotation force generated from the driving force generating means to the compression member; and bearing plates for supporting an axial load and a radial load of the rotational shaft, wherein, a space portion having predetermined volume is formed at a sliding part between the rotational shaft and the bearing plate where the axial load of the rotational shaft is supported, and a connection passage for connecting outside of the cylinder to the space portion in order to introduce discharged gas outside the cylinder into the space portion is formed.

2. The compressor of claim 1 , wherein the space portion is formed in an inner surface of the bearing plate.

3. The compressor of claim 2, wherein the space portion is formed

in the rotational shaft.

4. The compressor of claim 2, wherein a plurality of the space portions are formed with a same interval.

5. The compressor of claim 2, wherein the space portions are formed as a ring shape in a plane view.

6. The compressor of claim 2, wherein the space portions are formed as a circular arc shape in a plane view.

7. The compressor of claim 2, wherein the space portions are symmetrically formed in the radial direction of the rotational shaft in a plan view.

8. The compressor of claim 2, wherein a sectional area of the space portion is formed to be larger than a sectional area of the connection passage.

9. The compressor of claim 1 , wherein the connection passage is formed by penetrating the bearing plates.

10. The compressor of claim 1 , wherein the sectional area of the

connection passage is increased towards the space portion.

11. The compressor of claim 1 , wherein the space portion is formed in the rotational shaft.

12. A compressor comprising: a hermetic container to which a suction pipe and a discharge pipe are connected; a driving force generating means arranged in the hermetic container for generating a rotation force; a cylinder assembly composed of a cylinder installed in the hermetic container and forming a compression space, and bearing plates for hermetically sealing the compression space by covering the cylinder; a rotational shaft fixed to the driving force generating means and having a supporting portion integrally enlarged in a radial direction of the rotational shaft, said supporting portion for supporting an axial load of the rotational shaft on the bearing plates rotatably; a compression member arranged in the cylinder assembly by being fixed to a circumference of the supporting portion of the rotational shaft and having a cam surface of a predetermined curvature in order to vary a capacity of the compression space; and

vanes for dividing the compression space into suction regions and compression regions by being reciprocated towards inner and outer side directions of the cylinder assembly along the cam surface of the compression member when the compression member is rotated, wherein, space portion having predetermined volume is formed between the supporting portion of the rotational shaft and the bearing plate, and a connection passage for connecting outside of the cylinder and the space portions in order to introduce discharged gas outside the cylinder assembly into the space portions is formed.

13. The compressor of claim 12, wherein the space portion is formed in the bearing plate.

14. The compressor of claim 13, wherein the space portion is formed in the supporting portion of the rotational shaft.

15. The compressor of claim 13, wherein the space portion is formed as a ring shape in a plane view.

16. The compressor of claim 13, wherein a plurality of the space portions are formed with a same interval and formed symmetrically on the basis of a radial direction of the rotational shaft.

17. The compressor of claim 13, wherein sectional areas of the space portions are formed to be larger than a sectional area of the connection passage.

18. The compressor of claim 12, wherein the space portions are formed at the bearing plates and the supporting portion of the rotational shaft, respectively.

19. The compressor of claim 12, wherein the connection passage is formed by penetrating the bearing plates.

20. The compressor of claim 12, wherein a sectional area of the connection passage is increased towards the space portion.