WO2005008070A1

WO2005008070A1 - Compressor with reduced pressure pulsation and noise

Info

Publication number: WO2005008070A1
Application number: PCT/KR2003/002819
Authority: WO
Inventors: Jang-Woo Lee; Young-Jong Kim
Original assignee: Lg Electronics Inc.
Priority date: 2003-07-18
Filing date: 2003-12-23
Publication date: 2005-01-27
Also published as: KR20050009590A; KR100524790B1; AU2003285795A1

Abstract

A compressor comprises a cylinder (30) having a compression space therein; a compression member (23) disposed inside the compression space, and rotated with varying a volume (V) of the compression space; a rotational shaft (21) fixed to a driving force generating unit for transmitting a rotational force generated at the driving force generating unit to the compression member (23); a bearing plate (40, 50) where axial-directional and radial-directional loads of the rotational shaft are supported, a vane (60, 70) reciprocating in an inward/outward direction of the cylinder along a surface of the compression member (23) when the compression member (23) is rotated, and dividing the compression space into a suction region (V1a, V2a) and a compression region (V1b, V2b); a cavity (48, 58) formed in the rotational shaft (21) for having a predetermined volume; and a communication path (49, 59) formed in the bearing plate (40, 50) through which the compression region and the cavity (48, 49) are temporarily communicated with each other by rotation of the rotational shaft (21).

Description

Compressor with reduced pressure pulsation and noise

TECHNICAL FIELD The present invention relates to a compressor capable of reducing

pressure pulsation and discharge noise by preventing over-compression of a

fluid.

BACKGROUND ART In general, a compressor is an apparatus converting mechanical

energy into compression energy of a fluid, and is largely classified into a

reciprocating compressor, a scroll compressor, a centrifugal compressor and

a rotary compressor.

Among those compressors, the rotary compressor is a compressor in

which a rotational body is rotated in a state that an internal space of a

cylinder is divided into a suction region and a compression region by

inserting a vane into the rotational body so that the suction region and the

compression region are sequentially converted into one another, sucking,

compressing and discharging a compressible fluid.

Hereinafter, the rotary compressor as above will be described. FigJ is a longitudinal sectional view illustrating a main part of a

compressor according to the conventional art, Fig.2 is a perspective view

illustrating a partially cut compression part of a compressor according to the

conventional art, and Fig.3 is a plane view illustrating a compression part of a compressor according to the conventional art.

As shown in FigsJ and 2, a conventional compressor largely includes

a hermetic casing 110 communicating with a suction pipe 135 and with a

discharge pipe (not shown); a driving force generating unit 112 disposed

inside the hermetic casing 110, and for generating a rotational force; a

compression part 114 disposed inside the hermetic casing 110 to be isolated

from the driving force generating unit 112 at a predetermined interval

therebetween, and for sucking, compressing and discharging a fluid by the

rotational force generated from the driving force generating unit 112. Like a general electric motor, the driving force generating unit 112

includes a stator 116 adhesively fixed to an inner circumferential surface of

the hermetic casing 110; and a rotor 118 disposed maintaining a certain air

gap from an inner circumferential surface of the stator 116, and for

generating a rotational force by an electromagnetic interaction between itself

and the stator 116.

The compression part 114 includes a cylinder assembly 131 disposed

inside the hermetic casing 110, and forming a compression space (V) where

a fluid which is sucked from the outside is compressed; a rotational shaft 120

rotatably fixed to the cylinder assembly 131 , and also adhesively fixed to an

inner circumferential surface of the rotor 118 to be rotated with the rotor 118

when the rotor 118 is rotated 118; a compression member 123 coupled to the

rotational shaft 120 to be rotated therewith, and dividing the compression

space (V) in the cylinder assembly 131 into a first space (V1) and a second space (V2); and a first vane 160 and a second vane 170 which are in contact

with an upper surface and a lower surface of the compression member 123

respectively, and thus reciprocating in an inward/outward direction of the

compression space (V) along the upper surface and the lower surface of the

compression member 123 when the compression member 123 is rotated,

dividing the first and second spaces (V1), (V2) into suction regions (Via),

(V2a) and compression regions (V1b), (V2b) respectively.

The cylinder assembly 131 includes a cylinder 130 formed in a

cylindrical shape, and having one side where a suction path 136

communicating with the suction pipe 135 and thus through which a fluid is

sucked to the first space (V1) and the second space (V2) is formed; and a

first bearing plate 140 and a second bearing plate 150 fixed to both sides of

the cylinder 130, forming the compression space together with the cylinder

130, and supporting the rotating shaft. As shown in Fig.3, the first and second bearing plates 140,150 are

formed in a disc form with a predetermined thickness and an area, and

include journal portions 142, 152 extended from their centers with having a

predetermined height and an outer diameter, and whose insides are

penetrated so that the rotational shaft 120 is rotatably inserted therein; a first

vane slot 144 and a second vane slot 154 formed penetrating the first and

second bearing plates 140, 150 at one side of the journal portions 142, 152

so that the first and second vanes 160, 170 are inserted therein respectively;

discharge paths 146, 156 formed at one side of the first and second vane slots 144, 154 respectively, and through which a compressed fluid is

discharged from the compression space (V) of the cylinder assembly 131 ;

and an opening/closing member 180 mounted toward an outlet of the

discharge paths 146, 156, and for opening/closing the discharge paths 146.

156. In addition, a first discharge muffler 145 and a second discharge

muffler 155 covers an upper part of the first bearing plate 140 and a lower

part of the second bearing plate 150 respectively so as to reduce discharge

noise generated when the compressed fluid is discharged.

- The rotational shaft 120 includes a shaft portion 121 formed so as to

have a certain outer diameter and a predetermined length, and inserted in

the journal portions 142, 152 of the first and second bearing plates 140, 150;

and a support portion 122 integrally formed at a circumference of the shaft

portion 121 , coupled with the compression member 123 in the cylinder

assembly 131 , and supported on inner surfaces of the first and second

bearing plates 140, 150. Herein, the support portion 122 of the rotational

shaft 120 is concentric with the shaft portion 121 the rotational shaft 120, and

an oil path 125 is formed penetrating the shaft portion 121 so that oil within a

lower portion of the hermetic casing 11 can be upwardly supplied. The compression member 123 is formed in a disc shape in a plane

view so that its outer circumferential surface slidably contacts with the inner

circumferential surface of the cylinder 130. And also, the compression

member 123 is formed to have a cam surface with a sinuous curve having a predetermined thickness from the inner circumferential surface thereof to its

outer circumferential surface in a laterally projective view. Thus, a surface D1

having the top dead point is rotated sliding on a lower surface of the first

bearing plate 140, and a surface D2 having the bottom dead point is rotated

sliding on an upper surface of the second bearing plate 150.

The first vane 160 and the second vane 170 are formed into a

rectangular board shape, and are adhered to the cam surface of the

compression member 123 in the compression space (V) of the cylinder

assembly 131. So, when the compression member 123 is rotated, the first

vane 160 and the second vane 170 vertically reciprocate along the curve of

cam surface of the compression member 123, dividing the compression

spaces (V1), (V2) into suction regions (Via), (V2a) and compression regions

(V1b), (V2b).

In addition, the first and second vanes 160, 170 are elastically

supported by elastically supporting members 190 installed at the first and

second bearing plates 140, 150.

Operations of the compressor according to the conventional art

constructed as above will now be described.

First, when the rotational shaft 120 is rotated by a driving force of the

driving force generating unit 112, the compression member 123 coupled to

the rotational shaft 120 in the cylinder assembly 131 is simultaneously

rotated.

At this time, the first space (V1) positioned at an upper portion of the compression member 123 is divided into a suction region Via and a

compression region V1b on the basis of the top dead point (D1) of the

compression member 123 and the first vane 160. And, the second space

(V2) positioned at an lower portion of the compression member 123 is

divided into a suction region (V2a) and a compression region (V2b on the

basis of the bottom dead point (D2) of the compression member 123 and the

second vane 170.

In such a state, the top dead point (D1) and the bottom dead point

(D2) of the compression member 123 are moved by the rotation of the

compression member 123, varying volumes of the suction regions (Via),

(V2a) and the compression region (V1b), (V2b) of the first and second

spaces (V1), (V2). At this time, the first vane 160 and the second vane 170

reciprocate in directions opposite to each other on the basis of the

compression member 123. Accordingly, the fluid is sucked into each suction region (Via), (V2a)

of the first space (V1) and the second space (V2) through the suction path

136, and gradually compressed. Then, at the moment when the pressure of

the fluid in the compression regions (V1b), (V2b) reaches discharge pressure,

the compressed fluid is discharged outside the cylinder assembly 131

through discharge paths 146, 156 of each compression space (V1), (V2).

And, the fluid discharged outside the cylinder assembly 131 is

discharged outside the hermetic casing through the discharge pipe (not

shown) via the first and second mufflers 145, 155 and the inside of the hermetic casing 110.

In the compressor according to the conventional art constructed and

operating as above, the pressure of the fluid in the compression regions

(V1b), (V2b) is gradually increased by the rotation of the compression

member 123, and then at the moment of reaching the discharge pressure,

the fluid is discharged through the discharge paths 146, 156 with pushing the

opening/closing member 180. But, at the moment when the pressure of the

fluid in the compression regions (V1b), (V2b) reaches the discharge pressure,

the fluid is over-compressed, thereby generating pressure pulsation and

discharge noise, and degrading the compression performance of the

compressor.

DISCLOSURE OF THE INVENTION Therefore, it is an object of the present invention to provide a

compressor capable of reducing pressure pulsation and discharge noise

generated when a compressed fluid is discharged, and improving its

performance by reducing a loss due to over-compression of a fluid.

To achieve the above object, there is provided a compressor including

a cylinder disposed inside a hermetic casing, and having a compression

space therein; a compression member disposed inside the compression

space of the cylinder, and rotated with varying a volume of the compression

space; a rotational shaft fixed to a driving force generating unit, and

transmitting a driving force generated at the driving force generating unit to the compression member; a bearing plate on which axial-directional and

radial-directional loads of the rotational shaft are supported, and having a

discharge path through which a compressed fluid is discharged; a vane

reciprocating in an inward/outward direction of the cylinder along a surface of

the compression member in rotation of the compression member, and

dividing the compression space into a suction region and a compression

region; a cavity formed at the rotational shaft so as to have a predetermined

volume; and a communication path formed at the bearing plate, and for

making the compression region and the cavity temporarily communicate with

each other

BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a longitudinal sectional view illustrating a main part of a

compressor according to the conventional art; Fig.2 is a perspective view illustrating a partially cut compression part

of a compressor according to the conventional art;

Fig.3 is a plane view illustrating a compression part of a compressor

according to the conventional art;

Fig.4 is a longitudinal sectional view illustrating a main part of a

compressor according to the present invention;

Fig.5 is a perspective view illustrating a partially cut compression part

of a compressor according to the present invention;

Fig.6 is a plane view illustrating a compression part of a compressor according to the present invention;

Fig.7 is a longitudinal sectional view illustrating a compression part of

a compressor according to the present invention; and

Figs.δA to 8C are operational state views illustrating an operation

process of a compressor according to the present invention.

MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment according to the present

invention will now be described with reference to accompanying drawings. Fig.4 is a longitudinal sectional view illustrating a main part of a

compressor according to the present invention, Fig.5 is a perspective view

illustrating a partially cut compression part of a compressor according to the

present invention, Fig.6 is a plane view illustrating a compression part of a

compressor according to the present invention, and Fig.7 is a longitudinal

sectional view illustrating a compression part of a compressor according to

the present invention. As shown therein, the compressor according to the

present invention largely includes a hermetic casing 10 communicating with a

suction pipe 35 and with a discharge pipe (not shown); a driving force

generating unit 12 disposed inside the hermetic casing 10, and for generating

a rotational force; and a compression part 14 disposed inside the hermetic

casing 10 to be isolated from the driving force generating unit 12 at a

predetermined interval therebetween, and for sucking, compressing and

discharging a compressible fluid by the rotational force generated from the driving force generating unit 12.

Like a general electric motor, the driving force generating unit 12

includes a stator 16 adhesively fixed to an inner circumferential surface of the

hermetic casing 10; and a rotor 18 disposed maintaining a certain air gap

from an inner circumferential surface of the stator 16, and for generating a

rotational force by an electromagnetic interaction between itself and the

stator 16.

The compression part 14 includes a cylinder assembly 31 disposed

inside the hermetic casing 10, and forming a compression space (V) where

the fluid sucked from the outside is compressed; a rotational shaft 20

rotatably fixed to the cylinder assembly 31 , and adhesively fixed to an inner

circumferential surface of the rotor 18 to be rotated therewith when the rotor

18 is rotated; a compression member 23 coupled to the rotational shaft 20 to

be rotated, and dividing the compression space (V) in the cylinder assembly

31 into a first space (V1) and a second space (V2); and a first vane 60 and a

second vane 70 which are in contact with an upper surface and a lower

surface of the compression member 23 respectively and reciprocate in an

inward/outward direction of the compression space (V) along the upper

surface and the lower surface of the compression member 23 when the

compression member 23 is rotated, dividing the first and second spaces (V1),

(V2) into suction regions (Via), (V2a) and compression regions (V1b), (V2b)

respectively.

The cylinder assembly 31 includes a cylinder 30 formed in a cylindrical shape, and having one side where a suction path 36

communicating with the suction pipe 35, and through a fluid is sucked into

the first space (V1) and the second space (V2) is formed; and a first bearing

plate 40 and a second bearing plate 50 fixed at both sides of the cylinder 30,

forming the compression space together with the cylinder 30, and supporting

an axial-directional load of the rotational shaft 20 and a radial-directional load

thereof.

As shown in Fig.6, the first and second bearing plates 40, 50 are

formed in a disc shape with a certain thickness and an area, and include

journal portions 42, 52 extended from their centers to have a predetermined

height and an outer diameter, and whose inside are penetrated so that the

rotational shaft 20 is rotatably inserted therein; a first vane slot 44 and a

second vane slot 54 formed penetrating the first and second bearing plates

40, 50 at one side of the journal portions 42, 52 so that the first and second

vanes 60, 70 are inserted therein; discharge paths 46, 56 formed at one side

of the first and second vane slot 44, 54, and through which the compressed

fluid is discharged from the compression space (V) of the cylinder assembly

31 ; and an opening/closing member 80 mounted toward an outlet of the

discharge paths 46, 56, and for opening/closing the discharge paths 46, 56. In addition, a first discharge muffler 45 and a second discharge

muffler 55 covers an upper portion of the first bearing plate 40 and a lower

portion of the second bearing plate 50 respectively so as to reduce discharge

noise generated when the compressed fluid is discharged. The rotational shaft 20 includes a shaft portion 21 having a certain

diameter and a predetermined length, and inserted at the journal portions 42,

52 of the first and second bearing plates 40, 50; and a support portion 22

integrally formed at a circumference of the shaft portion 21 , coupled with the

compression member 23 inside the cylinder assembly 31 , and supported on

the inner surfaces of the first and second bearing plates 40, 50. That is, a

radial-directional load of the rotational shaft 20 is supported on radial bearing

surfaces (R) of the journal portions 42, 52 of the first and second bearing

plates 40, 50. And, an axial-directional load of the rotational shaft 20 is

supported by thrust bearing surfaces (T) of inner surfaces of the first and

second bearing plates 40, 50. The support portion 22 of the rotational shaft

20 is concentric with the shaft portion 21 of the rotational shaft 20, and an oil

path 25 is formed penetrating the shaft portion 21 so as to upwardly provide

oil within a lower portion of the hermetic casing 10. The compression member 23 is formed in a disc shape in a plane

view so that its outer circumferential surface slidably contacts with the inner

circumferential surface of the cylinder 30. And also, the compression member

23 is formed to have a cam surface with a sinuous curve having a

predetermined thickness from its inner circumferential surface to its outer

circumferential surface in a laterally projective view. Thus, a surface D1

having the top dead point is rotated sliding on a lower surface of the first

bearing plate 40, and a surface D2 having the bottom dead point is rotated

sliding on an upper surface of the second bearing plate 50. The first vane 60 and the second vane 70 are formed in a rectangular

board shape, and are adhered to a cam surface of the compression member

23 in the compression space (V) of the cylinder assembly 31. So, when the

compression member 23 is rotated, the first vane 60 and the second vane 70

reciprocate in an inward/outward direction of the cylinder assembly 31 along

the curve of the cam surface of the compression member 23, dividing the

compression spaces (V1), (V2) into suction regions (Via), (V2a) and

compression regions (V1 b), (V2b). In addition, the first and second vanes 60,

70 are elastically supported by elastically supporting members 90 installed at

the first and second bearing plates 40, 50 respectively.

At surfaces of the support portion 22 of the rotational shaft 20, which

is in contact with the thrust bearing surfaces (T) of the first and second

bearing plates 40, 50, cavities 48, 58 with a predetermined width and a

length are formed. At this time, in order to prevent generation of a dead

volume during compressing operation, preferably, the cavities 48, 58 are

formed so as not to communicate with the compression space (V1), (V2) of

the cylinder assembly 31.

At the first and second bearing plates 40, 50, communication paths

49, 59 are formed respectively so that the compression regions (V1b), (V2b)

and the cavities 48, 59 temporarily communicate with each other when the

pressure of the fluid in the compression regions (V1b), (V2b) reaches

predetermined pressure. The communication paths 49, 59 are formed in a

groove shape which is extended from one side of the discharge paths 46, 56 in an inward direction of the rotational shaft 20.

Accordingly, positions of the cavities 48, 58 are changed by the

rotation of the rotational shaft 20 on the basis of a central axis of the

rotational shaft 20, and then, at the moment when the pressure of the fluid in

the compression regions (V1b), (V2b) reaches predetermined pressure by

the rotation of the compression member 23, the cavities 48, 58 temporarily

communicate with the compression regions (V1b), (V2b) through the

communication paths 48, 58. Thusly, a part of the compressed fluid in the

compression regions (V1b), (V2b) is flowed into the cavities 48, 58, therefore

by the effect of dispersing the pressure, the over-compression of a fluid is

prevented, and pressure pulsation and discharge noise is reduced.

Herein, a point of time when the cavities 48,58 and the compression

regions (V1b), (V2b) temporarily communicate with each other can be set so

as to communicate with each other just before the pressure of the fluid in the

compression regions (V1b), (V2b) reaches the discharge pressure, that is,

just before the compressed fluid is discharged. And also, the point of time

when the cavities 48, 58 and the compression regions (V1b), (V2b)

temporarily communicate with each other can be set so as to communicate

with each other at a point when the pressure of the fluid in the compression

regions (V1b), (V2b) reaches the discharge pressure, that is, when the

compressed fluid is discharged outside the cylinder assembly 31 with

pushing the opening/closing member 80. The point of time is varied

according to a radial-directional distance between the cavities 48, 58 and a top dead point (D1) and a bottom dead point (D2) of the compression

member 23, and is selected and planned properly according to a fluid

capacity of a compressor and discharge pressure. In addition, volumes of the

cavities 48, 58 and the communication paths 49, 59 are selected and

planned properly according to the capacity of the compressor. Preferably,

cross-sectional areas of the communication paths 49, 59 are formed to be

smaller than horizontal-directional cross-sectional areas of the cavities 48, 58.

In a preferred embodiment of the present invention, the communication paths

49, 59 are extended from one side of the discharge paths 46, 56 in an inward

direction of the rotational shaft 20, but not limited thereto. So, the

communication paths 49, 59 can be formed at a position close to the

discharge paths 46, 56.

With reference to Figs.δA to 8C, the compressor according to the

present invention constructed as above will now be described. First, as shown in Fig.8A, when the rotational shaft 20 is rotated by a

driving force of the driving force generating unit 12, the compressor member

23 which is coupled to the support portion 22 of the rotational shaft 20 in the

cylinder assembly 31 is simultaneously rotated.

At this time, a first space (V1) positioned at an upper portion of the

compression member 23 is divided into a suction region (Via) to which a

fluid is sucked and a compression region (V1b) in which a fluid is

compressed, on the basis of a top dead point (D1) of the compression

member 23 and the first vane 60. And also, a second space (V2) positioned at a lower portion of the compression member 23 is divided into a suction

region (V2a) and a compression region (V2b) on the basis of a bottom dead

point (D2) of the compression member 123 and the second vane 70.

And, the positions of the top dead point (D1) and the bottom dead

point (D2) of the compression member 23 are changed by rotation of the

compression member 23, varying volumes of the suction regions (Via),

(V2a) and the compression regions (V1b), (V2b) of the first and second

spaces (V1), (V2). At this time, the first vane 60 and the second vane 70

reciprocate in directions opposite to each other on the basis of the

compression member 23.

At this time, the shaft portion 21 of the rotational shaft 20 is inserted

at journal portions 42, 52 of the first and second bearing plates 40, 50 and is

rotated, making a radial-directional load of the rotational shaft 20 supported

by radial bearing surfaces (R) of the journal portions. Both sides of the

support portion 22 of the rotational shaft 20 is rotated, making an axial-

directional load of the rotational shaft 20 supported by thrust bearing surfaces

(T) of the first and second bearing plates 40, 50. And, positions of the cavities

48, 58 formed at the support portions 22 of the rotational shaft 20 are

changed in a state of being isolated from the first and second space (V1),

(V2).

Accordingly, a fluid is sucked into each suction region (Via), (V2a) of

the first space (V1) and the second space (V2) through the suction path 36,

and then gradually compressed. As shown in Fig.δB, when the top dead point (D1) and the bottom

dead point (D2) of the compression member 23 are moved, the cavities 48,

58 formed at the support portion 22 of the rotational shaft 20 and the

discharge paths 46, 56 communicate with each other through the

communication paths 49, 59 formed at the first and second bearing plates 40,

50 just before the pressure of the compression regions (V1b), (V2b) reaches

discharge pressure, or at a point when the pressure of the fluid in the

compression regions (V1b), (V2b) reaches discharge pressure, that is, when

the compressed fluid is discharged outside the cylinder assembly 31 with

pushing the opening/closing member 60. Thusly, a part of the compressed

fluid in the compression regions (V1b), (V2b) is flowed into the cavities 46, 56

through the communication paths 49, 59. Accordingly, over-compression of

the fluid is prevented, and pressure pulsation and generation of noise due to

over-compression of the fluid are prevented. As shown in Fig.δC, as the positions of the top dead point (D1) and

the bottom dead point (D2) of the compression member 23 are continuously

changed, the compressed fluid in the compression regions (V1b), (V2b) is

discharged outside the cylinder assembly 31 through the discharge paths 46,

56 with pushing the opening/closing member δ0. The compressed fluid

discharged outside the cylinder assembly 31 is discharged outside the

hermetic casing 10 through the discharge pipe (not shown) via the first and

second discharge mufflers 45, 55 and the inside of the hermetic casing 10.

Such operations are sequentially performed, performing a cycle of suction, compression and discharge of the fluid.

In the compressor according to the present invention constructed and

operating as above, the cavities 43, 5δ formed at the support portion 22 of

the rotational shaft 20 and the compression regions (V1b), (V2b) temporarily

communicate with each other right before the pressure of the fluid in the

compression regions (V1b), (V2b) reaches the discharge pressure, or at a

point of reaching the discharge pressure. Therefore, a part of the

compressed fluid in the compression regions (V1 b), (V2b) is flowed into the

cavity 4δ, 58, thereby preventing over-compression of the fluid in the

compression region (V1b), (V2b), and reducing pressure pulsation and

discharge noise. Also, as the cavities 48, 58 and the discharge paths 46, 56

only temporarily communicate with each other by the rotation of the rotational

shaft 20, the cavities 48, 58 do not serve as the dead volume and so, forming

the cavities 48, 58 has a very small effect on the performance of the

compressor.

As so far described, the compressor according to the present

invention is planned so that the cavity formed at the rotational shaft and with

a predetermined volume and the compression region temporarily

communicate with each other through the communication path right before

the pressure of the fluid in the compression region where the fluid is

compressed, reaches the discharge pressure, or at a point when the

pressure of the fluid in the compression region reaches the discharge

pressure, that is, when the compressed fluid is discharged outside the cylinder assembly through the discharge path. Therefore, a part of the

compressed fluid in the compression region is flowed into the cavity, thereby

preventing over-compression of the fluid in the compression region, and

reducing pressure pulsation and discharge noise. 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 disposed inside a hermetic casing, and having a

compression space therein; a compression member disposed inside the compression space of

the cylinder, and rotated with varying a volume of the compression space; a rotational shaft fixed to a driving force generating unit, and

transmitting a rotational force generated at the driving force generating unit to

the compression member; a bearing plate where axial-directional and radial-directional loads of

the rotational shaft are supported, having a discharge path through which a

compressed fluid is discharged; a vane reciprocating in an inward/outward direction of the cylinder

along a surface of the compression member when the compression member

is rotated, and dividing the compression space into a suction region and a

compression region; a cavity formed in the rotational shaft for having a predetermined

volume; and a communication path formed in the bearing plate through which the

compression region and the cavity are temporarily communicated with each

other by rotation of the rotational shaft.

2. The compressor of claim 1 , wherein the communication path

is formed in a groove shape extended from one side of the discharge path.

3. The compressor of claim 1 , wherein the cavity and the

compression region communicate with each other right before a compressed

fluid is discharged.

4. The compressor of claim 1 , wherein the cavity and the

compression region communicate with each other at a point when a

compressed fluid is discharged.

5. The compressor of claim 1 , wherein the cavity is formed in a

portion of the rotational shaft where is in contact with the bearing plate.

6. The compressor of claim 1 , wherein a cross-sectional area of

the cavity is formed to be greater than that of the communication path.

7. A compressor comprising: a driving force generating unit disposed inside a hermetic casing for

generating a rotational force; a cylinder disposed inside the casing and having a compression

space therein; a bearing plate covering the cylinder to close the compression space, and having a discharge path through which a compressed fluid is discharged; a rotational shaft rotatably fixed to the driving force generating unit,

and having a support portion integrally formed in a circumferential direction

thereof and for making an axial-directional load supported on the bearing

plate; a compression member fixed at a circumference of the support

portion of the rotational shaft, disposed inside the cylinder, formed in a disc

shape in a plane view so that an outer circumference surface thereof slidably

contacts with an inner circumferential surface of the cylinder, and formed to

have a sinuous curve of a predetermined thickness in laterally projective

view; a vane reciprocating in an inward/outward direction of the cylinder

along the surface of the compression member with dividing the compression

space into a suction region and a compression region; a cavity formed at a portion of the support portion of the rotational

shaft, which is in contact with the bearing plate, and having a predetermined

volume; and a communication path formed in the bearing plate, through which a

compressed fluid in the compression region is temporarily flowed into the

cavity by rotation of the rotational shaft.

6. The compressor of claim 7, wherein the communication path

is formed in a groove shape extended from one side of the discharge path in a central direction of the rotational shaft.

9. The compressor of claim 7, wherein the cavity and the

compression region communicate with each other right before the

compressed fluid is discharged.

10. The compressor of claim 7, wherein the cavity and the

compression region communicate with each other at a point when the

compressed fluid is discharged.