Description

2 STAGE ROTARY COMPRESSOR Technical Field

[1] The present invention relates to a 2 stage rotary compressor, and more particularly, to a 2 stage rotary compressor inducing refrigerant inflow portions designed to be suitable for compression capability of each of a low pressure compression assembly and a high pressure compression assembly. Background Art

[2] In general, a compressor is a mechanical apparatus that receives power from a power generation apparatus such as an electric motor, a turbine or the like and compresses air, refrigerant or various operation gases to raise a pressure. The compressor has been widely used in an electric home appliance such as a refrigerator and an air conditioner, or in the whole industry.

[3] The compressor is roughly classified into a reciprocating compressor wherein a compression space to/from which an operation gas is sucked and discharged is defined between a piston and a cylinder, and the piston is linearly reciprocated inside the cylinder to compress refrigerant, a rotary compressor wherein a compression space to/ from which an operation gas is sucked and discharged is defined between an eccentrically-rotated roller and a cylinder, and the roller is eccentrically rotated along an inner wall of the cylinder to compress refrigerant, and a scroll compressor wherein a compression space to/from which an operation gas is sucked and discharged is defined between an orbiting scroll and a fixed scroll, and the orbiting scroll is rotated along the fixed scroll to compress refrigerant.

[4] Particularly, the rotary compressor has been developed to a twin rotary compressor, wherein two rollers and two cylinders are provided at upper and lower portions, and the pairs of rollers and cylinders of the upper and lower portions compress some and the other of the entire compression capacity, and a 2 stage rotary compressor, wherein two rollers and two cylinders are provided at upper and lower portions, and the two cylinders communicate with each other so that one pair can compress relatively low pressure refrigerant and the other pair can compress relatively high pressure refrigerant passing through a low pressure compression step.

[5] Korean Registered Patent Publication 1994-0001355 discloses a rotary compressor.

An electric motor is positioned in a shell, and a rotation axis is installed to pass through the electric motor. In addition, a cylinder is positioned below the electric

motor, and an eccentric portion fitted around the rotation axis and a roller fitted onto the eccentric portion are positioned in the cylinder. A refrigerant discharge hole and a refrigerant inflow hole are formed in the cylinder, and a vane for preventing non- compressed low pressure refrigerant from being mixed with compressed high pressure refrigerant is installed between the refrigerant discharge hole and the refrigerant inflow hole. Moreover, a spring is installed at one end of the vane so that the eccentrically- rotated roller and the vane can be continuously in contact with each other. When the rotation axis is rotated by the electric motor, the eccentric portion and the roller are rotated along the inner circumference of the cylinder to compress refrigerant gas, and the compressed refrigerant gas is discharged through the refrigerant discharge hole.

[6] Korean Laid-Open Patent Publication 10-2005-0062995 suggests a twin rotary compressor. Referring to FIG. 1, two cylinders 1035 and 1045 for compressing the same capacity and a middle plate 1030 are provided to improve a compression capacity twice as much as that of an 1 stage compressor.

[7] Korean Laid-Open Patent Publication 10-2007-0009958 teaches a 2 stage rotary compressor. As illustrated in FIG. 2, a compressor 2001 includes an electric motor 2014 having a stator 2007 and a rotor 2008 at an inside upper portion of a hermetic container 2013, and a rotation axis 2002 connected to the electric motor 2014 includes two eccentric portions. A main bearing 2009, a high pressure compression element 2020b, a middle plate 2015, a low pressure compression element 2020a and a sub bearing 2019 are successively stacked from the side of the electric motor 2014 with respect to the rotation axis 2002. In addition, a middle tube 2040 is installed to introduce refrigerant compressed in the low pressure compression element 2020a into the high pressure compression element 2020b. Disclosure of Invention Technical Problem

[8] An object of the present invention is to provide a 2 stage rotary compressor which can improve compression efficiency, wherein a ratio of a diameter of a low pressure refrigerant inflow portion for introducing low pressure refrigerant into a low pressure compression assembly to a diameter of a middle pressure refrigerant inflow portion for introducing middle pressure refrigerant compressed in the low pressure compression assembly into a high pressure compression assembly exists within a predetermined range.

[9] Another object of the present invention is to provide a 2 stage rotary compressor

inducing a connection passage for connecting a low pressure refrigerant inflow portion to a middle pressure refrigerant inflow portion.

[10] A further object of the present invention is to provide a 2 stage rotary compressor, wherein an injection tube is connected to a connection passage. Technical Solution

[11] According to the present invention, there is provided a 2 stage rotary compressor, including: a hermetic container; a 2 stage compression assembly provided in the hermetic container and including a low pressure compression assembly, a middle plate and a high pressure compression assembly; a low pressure refrigerant inflow portion provided in the low pressure compression assembly to introduce low pressure refrigerant; and a middle pressure refrigerant inflow portion provided in the high pressure compression assembly to introduce middle pressure refrigerant compressed in the low pressure compression assembly, wherein a diameter of the middle pressure refrigerant inflow portion is larger than 0.5 times of a diameter of the low pressure refrigerant inflow portion and smaller than 1.1 times thereof. This configuration can prevent a pressure of middle pressure refrigerant sucked into the high pressure compression assembly from being excessively raised or dropped, by appropriately controlling a volume flow of refrigerant introduced into the high pressure compression assembly through the middle pressure refrigerant inflow portion.

[12] According to one aspect of the present invention, the diameter of the middle pressure refrigerant inflow portion is 0.6 times to 1.0 times of the diameter of the low pressure refrigerant inflow portion. In this configuration, an energy efficiency ratio (EER) can be improved over 9.8.

[13] According to another aspect of the present invention, the diameter of the middle pressure refrigerant inflow portion is 0.9 times to 1.0 times of the diameter of the low pressure refrigerant inflow portion. In this configuration, the EER can be improved over 10.0.

[14] Accordng to a further aspect of the present invention, the low pressure compression assembly includes a low pressure cylinder for supplying a space of compressing refrigerant, and the low pressure refrigerant inflow portion is a tube inserted to reach the refrigerant compression space of the low pressure cylinder. In this configuration, low pressure refrigerant can be stably supplied to the compression space inside the low pressure cylinder. Here, an inner diameter of the tube becomes a diameter of the low pressure refrigerant inflow portion.

[15] Accordng to a still further aspect of the present invention, the low pressure

compression assembly includes a low pressure cylinder for supplying a space of compressing refrigerant, and the low pressure refrigerant inflow portion includes a hole formed in the low pressure cylinder and a tube inserted into the hole. Here, when the hole is processed into a large inner diameter portion outside the cylinder and a small inner diameter portion inside the cylinder with a step difference, the tube for introducing refrigerant can be inserted only to the stepped portion. Therefore, it is convenient to install the tube for introducing refrigerant.

[16] According to a still further aspect of the present invention, the 2 stage rotary compressor further includes a middle pressure passage for connecting the low pressure refrigerant inflow portion to the middle pressure refrigerant inflow portion. In this configuration, refrigerant compressed in the low pressure compression assembly can be introduced into the high pressure compression assembly.

[17] According to a still further aspect of the present invention, the middle pressure passage is a U-shaped tube passing through the hermetic container. In this configuration, it is easy to install the tube for supplying the middle pressure passage.

[18] According to a still further aspect of the present invention, the middle pressure passage is an inner passage defined inside the 2 stage compression assembly. In this configuration, middle pressure refrigerant flows only in the hermetic container, so that vibration and noise of the entire compressor can be reduced. In addition, a length of the middle pressure passage through which middle pressure refrigerant flows is shortened to thereby reduce a pressure loss.

[19] According to a still further aspect of the present invention, the 2 stage rotary compressor further includes an injection tube connected to the middle pressure passage. In this configuration, gas phase refrigerant is separated from refrigerant passing through a condenser in a phase separator and injected into the 2 stage rotary compressor, so that compression efficiency of the compressor can be improved.

[20] According to a still further aspect of the present invention, the 2 stage rotary compressor further includes a middle pressure chamber positioned on the middle pressure passage. In this configuration, a phase difference between a discharge stroke and a suction stroke of the low pressure compression assembly and the high pressure compression assembly can be offset to stably supply middle pressure refrigerant to the high pressure compression assembly.

[21] According to a still further aspect of the present invention, the middle pressure chamber is defined by a bearing and a bearing cover. In this configuration, the middle pressure chamber can be easily formed without any separate member.

[22] According to a still further aspect of the present invention, the middle pressure chamber is positioned at any one of upper and lower portions of the 2 stage compression assembly. Advantageous Effects

[23] According to a 2 stage rotary compressor of the present invention, a size of a low pressure refrigerant inflow portion for introducing refrigerant into a low pressure compression assembly and a size of a middle pressure refrigerant inflow portion for introducing middle pressure refrigerant compressed in the low pressure compression assembly into a high pressure compression assembly can be controlled according to compression capability and volume flow of each compression assembly, thereby improving compression efficiency of the compressor.

[24] In addition, according to a 2 stage rotary compressor of the present invention, sizes of respective refrigerant inflow portions can be controlled according to structures thereof, thereby improving compression efficiency of the compressor. Brief Description of the Drawings

[25] FIG. 1 is a view illustrating one example of a conventional twin rotary compressor;

[26] FIG. 2 is a view illustrating one example of a conventional 2-stage stage rotary compressor;

[27] FIG. 3 is a schematic view illustrating one example of a cycle including a 2 stage rotary compressor;

[28] FIG. 4 is a view illustrating a 2 stage rotary compressor according to one embodiment of the present invention;

[29] FIG. 5 is a view illustrating a low pressure compression assembly of the 2 stage rotary compressor according to one embodiment of the present invention;

[30] FIGS. 6 and 7 are views illustrating portions of the 2 stage rotary compressor according to one embodiment of the present invention, seen from the top and bottom, respectively;

[31] FIG. 8 is a cutaway view illustrating the 2 stage rotary compressor according to one embodiment of the present invention;

[32] FIG. 9 is a view illustrating one example of a rotation axis provided in the 2 stage rotary compressor according to one embodiment of the present invention;

[33] FIG. 10 is a view illustrating a 2 stage rotary compressor with an injection tube installed therein according to one embodiment of the present invention;

[34] FIGS. 11 and 12 are schematic views illustrating suction diameters of the 2 stage

rotary compressor accordng to the present invention, in a state where a U-shaped tube and an inner passage are used as middle pressure passages, respectively;

[35] FIGS. 13 and 14 are views illustrating examples of the low pressure refrigerant inflow portion included in the 2 stage rotary compressor accordng to one embodment of the present invention, respectively;

[36] FIG. 15 is a view illustrating one example of a high pressure cylinder to compare dameters of middle pressure refrigerant inflow portions formed in various sizes; and

[37] FIG. 16 is a graph showing an EER by a ratio d2/dl of a dameter d2 of the middle pressure refrigerant inflow portion to a dameter dl of the low pressure refrigerant inflow portion. Mode for the Invention

[38] Hereinafter, preferred embodments of the present invention will be described in detail with reference to the accompanying drawings.

[39] FIG. 3 is a schematic view illustrating one example of a freezing cycle constructed by a 2 stage rotary compressor. The freezing cycle includes a 2 stage rotary c ompressor 100, a condenser 300, an evaporator 400, a phase separator 500, a 4 way valve 600, etc.. The condenser 300 constitutes an indoor unit, and the compressor 100, the evaporator 400 and the phase separator 500 constitute an outdoor unit. Refrigerant compressed in the compressor 100 is introduced into the condenser 300 through the 4 way valve 600. The compressed refrigerant gas exchanges heat with the ambient air and is condensed. The condensed refrigerant becomes a low pressure through an expansion valve. The refrigerant passing through the expansion valve is separated into gas and liquid in the phase separator 500. The liquid flows into the evaporator 400. The liquid is heat-exchanged and evaporated in the evaporator 400, introduced into an accumulator 200 in a gas phase, and transferred from the accumulator 200 to a low pressure compression assembly (not shown) through a refrigerant inflow tube 151 of the compressor 100. In addtion, the gas separated in the phase separator 500 is introduced into the compressor 100 through an injection tube 153. Middle pressure refrigerant compressed in the low pressure compression assembly of the compressor 100 and refrigerant transferred through the injection tube 153 are supplied to a high pressure compression assembly (not shown) of the compressor, compressed to a high pressure, and dscharged to the outside of the compressor 100 through a refrigerant dscharge tube 152.

[40] FIG. 4 is a view illustrating a 2 stage rotary compressor accordng to one embodment of the present invention. A 2 stage rotary compressor 100 accordng to

one embodment of the present invention includes a low pressure compression assembly 120, a middle plate 140, a high pressure compression assembly 130 and an electric motor 110 in a hermetic container 101 from the bottom. In addition, the 2 stage rotary compressor 100 includes a refrigerant inflow tube 151 connected to an accumulator 200, and a refrigerant discharge tube 152 for dscharging compressed refrigerant to the outside of the hermetic container 101, which pass through the hermetic container 101.

[41] The electric motor 110 includes a stator 111, a rotor 112 and a rotation axis 113.

The stator 111 has a lamination of ring-shaped electronic steel plates and a coil wound around the lamination. The rotor 112 also has a lamination of electronic steel plates. The rotation axis 113 passes through a center of the rotor 112 and is fixed to the rotor 112. When a current is applied to the electric motor 110, the rotor 112 is rotated due to a mutual electromagnetic force between the stator 111 and the rotor 112, and the rotation axis 113 fixed to the rotor 112 is rotated with the rotor 112. The rotation axis 113 is extended from the rotor 112 to the low pressure compression assembly 120 to pass through the central portions of the low pressure compression assembly 120, the middle plate 140 and the high pressure compression assembly 130.

[42] The low pressure compression assembly 120 and the high pressure compression assembly 130 may be stacked with the middle plate 140 positioned therebetween in the order of the low pressure compression assembly 120 - the middle plate 140 - the high pressure compression assembly 130 from the bottom. On the contrary, the low pressure compression assembly 120 and the high pressure compression assembly 130 may be stacked in the order of the high pressure compression assembly 130 - the middle plate 140 - the low pressure compression assembly 120 from the bottom. In addition, a lower bearing 161 and an upper bearing 162 are installed under and on the stacked assembly, regardless of the stacked order of the low pressure compression assembly 120, the middle plate 140 and the high pressure compression assembly 130 so as to facilitate the rotation of the rotation axis 113 and support load of respective vertically- stacked components of the 2 stage compression assembly. The upper bearing 162 is fixed to the hermetic container 101 by means of 3 -point weldng so as to support the load of the 2 stage compression assembly.

[43] The refrigerant inflow tube 151 passing through the hermetic container 101 from the outside is connected to the low pressure compression assembly 120. Moreover, the lower bearing 161 and a lower cover 171 are positioned under the low pressure compression assembly 120. A middle pressure chamber P is defined between the

lower bearing 161 and the lower cover 171. The middle pressure chamber P is a space m to which refrigerant compressed in the low pressure compression assembly 120 is discharged, and a space in which refrigerant is temporarily stored before it is introduced into the high pressure compression assembly 130. The middle pressure chamber P serves as a buffering space on a passage of flowing refrigerant from the m low pressure compression assembly 120 to the high pressure compression assembly 130.

[44] A discharge port (not shown) is formed in an upper portion of the upper bearing

162 positioned on the high pressure compression assembly 130. High pressure refrigerant dscharged from the high pressure compression assembly 130 through the discharge port of the upper bearing 162 is dscharged to the outside through the refrigerant dscharge tube 152 positioned at an upper portion of the hermetic container 101.

[45] An inner passage 180 connected to cause refrigerant to flow from the low pressure compression assembly 120 to the high pressure compression assembly 130 is formed in the lower bearing 161, the low pressure compression assembly 120, the middle plate 140 and the high pressure compression assembly 130. The inner passage 180 is vertically formed to be parallel with an axis drection of the compressor 100.

[46] FIG. 5 is a sectional view illustrating the low pressure compression assembly 120.

The low pressure compression assembly 120 includes a low pressure cylinder 121, a low pressure eccentric portion 122, a low pressure roller 123, a low pressure vane 124, a low pressure elastic member 125, a low pressure inflow hole 126, and a middle pressure dscharge hole 127. The rotation axis 113 passes through a central portion of the low pressure cylinder 121, and the low pressure eccentric portion 122 is fixed to the rotation axis 113. Here, the low pressure eccentric portion 122 may be integrally formed with the rotation axis 113. In addtion, the low pressure roller 123 is rotatably installed on the low pressure eccentric portion 122, so that the low pressure roller 123 is rolled and rotated along an inner dameter of the low pressure cylinder 121 due to the rotation of the rotation axis 113. The low pressure inflow hole 126 and the middle pressure dscharge hole 127 are formed at both sides of the low pressure vane 124. Moreover, a space inside the low pressure cylinder 121 is partitioned off by the low pressure vane 124 and the low pressure roller 123, so that refrigerant before compression and refrigerant after compression coexist in the low pressure cylinder 121. A portion partitioned by the low pressure vane 124 and the low pressure roller 123 and includng the low pressure inflow hole 126 is referred to as a low pressure re-

frigerant inflow portion S , and a portion includng the middle pressure discharge hole 127 is referred to as a middle pressure refrigerant discharge portion D . At this time, m the low pressure elastic member 125 is a means for applying force to the low pressure vane 124 so that the low pressure vane 124 can be continuously in contact with the low pressure roller 123. A vane hole 124h formed in the low pressure cylinder 121 to position the low pressure vane 124 therein penetrates through the low pressure cylinder 121 in a horizontal drection. The low pressure vane 124 is guided through the vane hole 124h, and the low pressure elastic member 125 imparting force to the low pressure vane 124 passes through the low pressure cylinder 121 and extends to the hermetic container 101 through the vane hole 124h. One end of the low pressure elastic member 125 contacts the low pressure vane 124 and the other end thereof contacts the hermetic container 101 to push the low pressure vane 124 to be continuously in contact with the low pressure roller 123. [47] In addition, a middle pressure communication hole 120a is formed in the low pressure cylinder 121 so that refrigerant compressed in the low pressure compression assembly 120 can be introduced into the high pressure compression assembly 130 via the middle pressure chamber P defined by the lower bearing 161. The middle pressure m communication hole 120a is formed to avoid the refrigerant inflow tube 151 so that the middle pressure communication hole 120a can not overlap with the refrigerant inflow tube 151 inserted into the low pressure inflow hole 126, i.e., the inner passage 180 can not overlap with the refrigerant inflow tube 151. Even if the middle pressure communication hole 120a partially overlaps with the refrigerant inflow tube 151, it causes middle pressure refrigerant to flow from the middle pressure chamber P to the high m pressure compression assembly 130. However, in this case, a loss may occur as much as a sectional area of the inner passage 180 overlapping with the refrigerant inflow tube 151. In addition, since refrigerant bypasses the refrigerant inflow tube 151, a pressure may be lowered.

[48] As shown in FIG. 5, when the low pressure eccentric portion 122 is rotated due to the rotation of the rotation axis 113 and the low pressure roller 123 is rolled along the low pressure cylinder 121, a volume of the low pressure inflow portion S is increased, so that the low pressure inflow portion S has a low pressure. Therefore, refrigerant is introduced through the low pressure inflow hole 126. Meanwhile, a volume of the middle pressure discharge portion D is decreased, so that refrigerant filled in the m middle pressure discharge portion D is compressed and discharged through the m middle pressure discharge hole 127. The volumes of the low pressure inflow portion S

and the middle pressure discharge portion D are continuously changed according to m the rotation of the low pressure eccentric portion 122 and the low pressure roller 123, and compressed refrigerant is discharged in every one rotation. [49] FIGS. 6 to 8 are views illustrating portions of the 2 stage rotary compressor according to one embodiment of the present invention. The lower bearing 161, the low pressure compression assembly 120, the middle plate 140 and the high pressure compression assembly 130 are successively stacked from the bottom. As described above, low pressure refrigerant is introduced into the low pressure cylinder 121 through the refrigerant inflow tube 151 and the low pressure inflow hole 126, compressed, and discharged to the middle pressure chamber P which is a space m restricted by a bottom surface of the low pressure compression assembly 120, the lower bearing 161 and the lower cover 171 through the middle pressure discharge hole 127. A middle pressure discharge hole 161h is formed in the lower bearing 161 to overlap with the middle pressure discharge hole 127, and a valve (not shown) is installed under the middle pressure discharge hole 16 Ih of the lower bearing 161. When refrigerant compressed in the middle pressure discharge portion D of the low m pressure compression assembly 120 is compressed to a predetermined pressure, it is discharged to the middle pressure chamber P . The refrigerant discharged to the m middle pressure chamber P is introduced into the high pressure compression assembly m

130 via the middle pressure communication hole 161a formed in the lower bearing 161, the middle pressure communication hole 120a formed in the low pressure cylinder 121, a middle pressure communication hole 140a formed in the middle plate 140 and a middle pressure inflow groove 130a formed in the high pressure cylinder 131. The middle pressure communication hole 161a of the lower bearing 161, the middle pressure communication hole 120a of the low pressure compression assembly 120, the middle pressure communication hole 140a of the middle plate 140 and the middle pressure inflow groove 130a of the high pressure compression assembly 130 define the inner passage 180 for middle pressure refrigerant compressed in the low pressure compression assembly 120. Here, the middle pressure inflow groove 130a of the high pressure compression assembly 130 is formed in the shape of an inclined groove to communicate with an inner space of the high pressure cylinder 131. Some lower portion of the middle pressure inflow groove 130a is in contact with the middle pressure communication hole 140a of the middle plate 140 to be a part of the inner passage 180. Compressed middle pressure refrigerant is introduced into the high pressure cylinder 131 through the middle pressure inflow groove 130a. When middle

pressure refrigerant is supplied to the high pressure compression assembly 130 through the inner passage 180, the high pressure compression assembly 130 compresses the middle pressure refrigerant to a high pressure in the same operation principle as that of the low pressure compression assembly 120.

[50] As set forth above, when the inner passage 180 for middle pressure refrigerant is not defined by a separate tube but formed in the hermetic container 101, noise can be suppressed and a length of the inner passage 180 can be reduced, so that a refrigerant pressure loss caused by a resistance can be reduced. In the above description, although the middle pressure chamber P is formed at the lower bearing 161, it may be formed m at any one of the upper bearing 162 and the middle plate 140. Accordngly, detailed configuration may be slightly changed. However, in every case, the inner passage 180 is formed in the 2 stage compression assembly to guide middle pressure refrigerant compressed in the middle pressure compression assembly 120 to the high pressure compression assembly 130. In this configuration, since a length of the passage for guidng middle pressure refrigerant is reduced, a flow loss can be minimized, and since refrigerant obes not pass through a connection tube passing through the hermetic container 101, noise and vibration can be suppressed.

[51] Here, in order to prevent the inner passage 180 from being blocked by the refrigerant inflow tube 151, the middle pressure communication hole 120a of the low pressure compression assembly 120, the middle pressure communication hole 140a of the middle plate 140 and the middle pressure inflow groove 130a of the high pressure compression assembly 130 constituting the inner passage 180 are spaced apart from the refrigerant inflow tube 151, as seen in an axis drection of the compressor 100.

[52] The middle pressure communication hole 161a of the lower bearing 161 is formed to avoid an insertion position of the refrigerant inflow tube 151 connected to the low pressure cylinder 121 so that the middle pressure communication hole 161a can not be blocked by the refrigerant inflow tube 151. The refrigerant inflow tube 151 is inserted into the low pressure inflow hole 126 formed in the low pressure cylinder 121. The low pressure inflow hole 126 is adjacent to the low pressure vane insertion hole 124h into which the low pressure vane 124 (see FIG. 5) is to be inserted. As the low pressure inflow hole 126 is dstant from the low pressure vane 124 (shown in FIG. 5), a dead volume which obes not contribute to compression of refrigerant is increased in an inner space of the low pressure cylinder 121.

[53] In addtion, the middle pressure inflow groove 130a of the high pressure cylinder

131 is not formed from the lower to upper portions of the high pressure cylinder 131,

but inclinedly formed from the lower portion to the inner space of the high pressure cylinder 131. Here, the middle pressure inflow groove 130a is adjacent to a high pressure vane hole 134h into which a high pressure vane (not shown) is to be inserted. As in the low pressure compression assembly 120, when the middle pressure inflow groove 130a is adjacent to the high pressure vane (not shown), a dead volume is reduced in the inner space of the high pressure cylinder 131.

[54] The low pressure vane 124 and the high pressure vane (not shown) are positioned on the same axis. Accordngly, the middle pressure communication hole 161a formed in the lower bearing 161 and the middle pressure inflow groove 130a formed in the high pressure cylinder 131 are not formed on the same axis, but spaced apart from each other in a horizontal drection. Accordng to a third embodment of the present invention, the middle pressure communication hole 120a of the low pressure cylinder 121 and the middle pressure communication hole 140a of the middle plate 140 are formed in a spiral shape to connect the middle pressure communication hole 161a of the lower bearing 161 to the middle pressure inflow groove 130a of the high pressure cylinder 131. The middle pressure communication hole 120a of the low pressure cylinder 121 and the middle pressure communication hole 140a of the middle plate 140 are formed in a spiral shape to overlap with each other. That is, the middle pressure communication hole 120a of the low pressure cylinder 121 and the middle pressure communication hole 140a of the middle plate 140 overlap with each other to define a spiral communication hole. At this time, one end of the spiral communication hole overlaps with the middle pressure communication hole 161a of the lower bearing 161, and the other end thereof overlaps with the middle pressure inflow groove 130a of the high pressure cylinder 131. Here, one end of the middle pressure communication hole 120a of the low pressure cylinder 121 is connected to the middle pressure communication hole 161a of the lower bearing 161. That is, one end of the middle pressure communication hole 120a of the low pressure cylinder 121 which is in contact with the middle pressure communication hole 161a of the lower bearing 161 is formed in a vertical drection of the low pressure cylinder 121, and the other portion of the middle pressure communication hole 120a is entirely formed in a spiral shape as a bottom end thereof is gradually heightened from one end to the other end. On the contrary, the other end of the middle pressure communication hole 140a of the middle plate 140, i.e., the other end of the spiral communication hole overlapping with the middle pressure inflow groove 130a of the high pressure cylinder 131 is formed in a vertical drection of the middle plate 140. In addtion, the middle pressure communication hole

140a is entirely formed in a spiral shape as a top end thereof is gradually heightened from one end overlapping with the middle pressure communication hole 161a of the lower bearing 161 to the other end.

[55] In a case where the middle pressure communication hole 120a of the low pressure cylinder 121 and the middle pressure communication hole 140a of the middle plate 140 are formed in a spiral shape, when refrigerant flows through the middle pressure communication hole 120a of the low pressure cylinder 121 and the middle pressure communication hole 140a of the middle plate 140, a resistance imparted to the refrigerant is reduced. Meanwhile, the middle pressure communication hole 120a of the low pressure cylinder 121 and the middle pressure communication hole 140a of the middle plate 140 may be formed in a circular arc shape with a constant top or bottom end height as well as in a spiral shape.

[56] Moreover, when the middle pressure communication hole 120a of the low pressure cylinder 121 and the middle pressure communication hole 140a of the middle plate 140 are formed in a spiral or circular arc shape, fastening holes 120b and 140b may be formed in central portions of the spiral or circular arc-shaped middle pressure communication holes 120a and 140a. Normally, the lower bearing 161, the low pressure cylinder 121, the middle plate 140, the high pressure cylinder 131 and the upper bearing 162 are fastened by means of bolts. Here, bolt fastening holes 161b, 120b, 130b, 140b and 162b should be formed to avoid various members and the inner passage, such as the refrigerant inflow tube 151, the middle pressure communication holes 161a, 120a, 140a and 162a, the middle pressure inflow groove 130a and the middle pressure discharge hole 127. In addtion, the fastening holes 161b, 120b, 130b, 140b and 162b should be formed in at least three positions to evenly disperse a fastening force to the entire compression assembly 105. At this time, the middle pressure communication hole 120a of the low pressure cylinder 121 and the middle pressure communication hole 140a of the middle plate 140 are longer than the middle pressure communication hole 161a of the lower bearing 161 and the middle pressure inflow groove 130a of the high pressure cylinder 131, which makes it dfficult to form the fastening holes 161b, 120b, 130b, 140b and 162b in a plural number. Accordingly, when the middle pressure communication hole 120a of the low pressure cylinder 121 and the middle pressure communication hole 140a of the middle plate 140 are formed in a spiral or circular arc shape, since the fastening holes 161b, 120b, 130b, 140b and 162b are formed in the centers of the spiral or circular arc shapes, the fastening holes 161b, 120b, 130b, 140b and 162b can be dspersively arranged in the entire

compression assembly 105.

[57] FIG. 9 is a view illustrating one example of the rotation axis provided in the 2 stage rotary compressor accordng to the present invention. A low pressure eccentric portion 122 and a high pressure eccentric portion 132 are coupled to the rotation axis 113. In order to reduce vibration, the low pressure eccentric portion 122 and the high pressure eccentric portion 132 are generally coupled to the rotation axis 113 with a phase difference of 180 °. In addition, the rotation axis 113 is a hollow axis, and oil communication holes 103a are formed below the low pressure eccentric portion 122 and over the high pressure eccentric portion 132. Moreover, a thin-plate stirrer 103b bent in a spiral shape is inserted into the rotation axis 113. The stirrer 103b is fitted into the rotation axis 113 and rotated with the rotation axis 113 during the rotation of the rotation axis 113. When the stirrer 103b is rotated due to the rotation of the rotation axis 113, oil filled in a lower portion of the hermetic container 101 (see FIG. 4) is lifted along the inside of the rotation axis 113 by means of the stirrer 103b. Some oil is discharged to the low pressure cylinder 121, the middle plate 140 and the high pressure cylinder 131 through the oil communication holes 103a formed in the rotation axis 113, thereby lubricating the low pressure roller 123 (see FIG. 5) and a high pressure roller (not shown).

[58] FIG. 10 is a view illustrating a compressor with an injection tube inserted thereinto accordng to a first embodment of the present invention. In a 2 stage compressor 100 accordng to the present invention, since an inner passage 180 is not a separate tube, an injection tube 153 for injecting refrigerant gas separated in a phase separator 500 may be installed in any portion of the inner passage 180. For example, a through hole 153h is formed in any one of a lower bearing 161, a middle plate 140 and a high pressure cylinder 131 constituting a middle pressure chamber P , and the injection tube 153 is m inserted into the through hole 153h so as to inject refrigerant gas. As shown in FIG. 8, in a state where the through hole 153h is formed to pass through a middle pressure dscharge hole 127 of a low pressure cylinder 121 or formed in the lower bearing 161, when the injection tube 153 is inserted into the through hole 153h, a pressure loss occurs along the middle pressure chamber P and the inner passage 180. However, m although liquid phase refrigerant is introduced through the injection tube 153, it is collected in a lower portion of the middle pressure chamber P , so that the compressor m

100 can be stably operated.

[59] FIGS. 11 and 12 are schematic views illustrating suction dameters of the 2 stage rotary compressor accordng to the present invention, in a state where a U-shaped tube

and an inner passage are used as middle pressure passages, respectively. [60] Referring to FIG. 11, according to one embodiment of the present invention using a U-shaped tube 182 as a middle pressure passage, the refrigerant inflow tube 151 is inserted into the low pressure compression assembly 120. Low pressure refrigerant introduced through the refrigerant inflow tube 151 is compressed in the low pressure compression assembly 120 and discharged to the middle pressure chamber P . m

Thereafter, refrigerant is introduced into the high pressure compression assembly 130 through the U-shaped tube 182 with both ends connected to the middle pressure chamber P and the high pressure compression assembly 130, compressed to a high m pressure, and discharged to the hermetic container 101. Here, a dameter of the low pressure inflow hole 126 (see FIG. 5) through which the refrigerant inflow tube 151 is inserted into the low pressure compression assembly 120 becomes a diameter dl of a low pressure refrigerant inflow portion. In addition, a dameter of one end of the U- shaped tube 182 connected to the middle pressure chamber P is equal to a dameter of m the other end thereof connected to the high pressure compression assembly 130, and the dameter of the U-shaped tube 182 is a dameter d2 of a middle pressure refrigerant inflow portion.

[61] Referring to FIG. 12, accordng to another embodment of the present invention using the inner passage 180 as a middle pressure passage, the refrigerant inflow tube 151 is inserted into the low pressure compression assembly 120, and middle pressure refrigerant compressed in the low pressure compression assembly 120 is introduced into the high pressure compression assembly 130 through the inner passage 180 defined in the 2 stage compression assembly 105. Like the embodment of the present invention using the U-shaped tube 182 as the middle pressure passage, a dameter of the low pressure inflow hole 126 (see FIG. 5) through which the refrigerant inflow tube 151 is inserted into the low pressure compression assembly 120 becomes a dameter dl of a low pressure refrigerant inflow portion. A dameter d2 of a middle pressure refrigerant inflow portion becomes a dameter of the inner passage 180.

[62] FIGS. 13 and 14 are views illustrating examples of the low pressure refrigerant inflow portion included in the 2 stage rotary compressor accordng to one embodment of the present invention, respectively. FIG. 13 shows a first example. In a case where a dameter of the low pressure inflow hole 126 formed in the low pressure cylinder 121 is constant from an outer dameter to an inner dameter of the low pressure cylinder 121, the constant dameter of the low pressure inflow hole 126 is a dameter dl of the low pressure refrigerant inflow portion.

[63] FIG. 14 shows a second example. A dameter of the low pressure inflow hole 126 is smaller on the inner dameter side of the low pressure cylinder 121 than the outer dameter side thereof. That is, the low pressure inflow hole 126 has a step difference. Here, a small dameter of the low pressure inflow hole 126 on the inner dameter side is a dameter dl of the low pressure refrigerant inflow portion. In a case where the low pressure inflow hole 126 has a step dfference, since an insertion position of the refrigerant inflow tube 151 (see FIG. 4) inserted into the low pressure inflow hole 126 is restricted, the refrigerant inflow tube 151 (see FIG. 4) can be easily installed.

[64] FIG. 15 is a view illustrating one example of the high pressure cylinder to compare dameters of middle pressure refrigerant inflow portions formed in various sizes, and FIG. 16 is a graph showing an EER by a ratio d2/dl of the dameter d2 of the middle pressure refrigerant inflow portion 136 to the dameter dl of the low pressure refrigerant inflow portion 126. As illustrated in FIGS. 15 and 16, the middle pressure refrigerant inflow portion 136 into which the U-shaped tube 182 (see FIG. 11) is to be inserted is formed in the high pressure cylinder 131. The dameter d2 of the middle pressure refrigerant inflow portion 136 may be smaller than, equal to and larger than the dameter dl (see FIG. 11) of the low pressure refrigerant inflow portion 126 (A, B and C). Here, in a case where the dameter d2 of the middle pressure refrigerant inflow portion 136 is excessively large, an inner volume of the high pressure cylinder 131 that can be substantially used for compression is reduced, and a suction pressure is dropped. That is, an actual compression dstance is shortened and a suction pressure is dropped to thereby increase a loss. Accordngly, it is preferable that the ratio d2/dl of the dameter d2 of the middle pressure refrigerant inflow portion 136 to the dameter dl of the low pressure refrigerant inflow portion 126 is smaller than 1.1.

[65] Meanwhile, in a case where the dameter d2 of the middle pressure refrigerant inflow portion 136 is excessively small, the actual compression dstance is lengthened and the inner volume of the high pressure cylinder 131 is increased. However, when middle pressure refrigerant flows, a flow loss occurs due to friction or the like, so that an entire loss increases. Thus, it is preferable that the ratio d2/dl of the dameter d2 of the middle pressure refrigerant inflow portion 136 to the dameter dl of the low pressure refrigerant inflow portion 126 is larger than 0.5.

[66] That is, preferably, the ratio d2/dl of the dameter d2 of the middle pressure refrigerant inflow portion 136 to the dameter dl of the low pressure refrigerant inflow portion 126 satisfies the following formula:

[67]

0.5<^- <l . l d\

[68] In this case, according to an experiment, the EER can be improved over 9.6. Particularly, in a case where the ratio d2/dl of the diameter d2 of the middle pressure refrigerant inflow portion 136 to the diameter dl of the low pressure refrigerant inflow portion 126 ranges from 0.6 to 1.0, the EER can be improved over 9.8.

[69] Most preferably, in a case where the ratio d2/dl of the diameter d2 of the middle pressure refrigerant inflow portion 136 to the diameter dl of the low pressure refrigerant inflow portion 126 has a value of 0.9 to 1.0, the EER can be improved over 10.0.

[70] FIG. 15 illustrates the high pressure cylinder provided in the 2 stage compressor according to one embodiment using the U-shaped tube as the middle pressure passage. On the other hand, in case of the high pressure cylinder according to another embodiment using the inner passage as the middle pressure passage, the dameter of the inner passage becomes the dameter d2 of the middle pressure refrigerant inflow portion 136, and the same condtions are used.

[71] The schematic operation principle of the 2 stage rotary compressor accordng to one embodment of the present invention will be explained with reference to FIGS. 3 to 10.

[72] Refrigerant circulated in the freezing cycle is temporarily stored in the accumulator

200 before being introduced into the compressor 100. The accumulator 200 serves as a temporary storage space of refrigerant and functions as a gas-liquid separator to introduce only gas into the compressor 100. Gaseous refrigerant flows from the accumulator 200 to the low pressure cylinder 121 of the low pressure compression assembly 120 through the refrigerant inflow tube 151. The refrigerant inflow tube 151 penetrates through the hermetic container 101 and is fixed to the hermetic container 101 by means of weldng. In addtion, the refrigerant inflow tube 151 is inserted into the refrigerant inflow hole 126 formed in the low pressure cylinder 121. The refrigerant inflow hole 126 is formed to reach the inner dameter of the low pressure cylinder 121. The refrigerant introduced into the inner space of the low pressure cylinder 121 through the refrigerant inflow hole 126 is compressed by volume variations of the spaces defined by the low pressure cylinder 121, the low pressure roller 123 and the low pressure vane 124 due to relative motion of the low pressure cylinder 121 and the low pressure roller 123. The compressed refrigerant is transferred

from the low pressure cylinder 121 to the high pressure cylinder 131 through the inner passage 180, and compressed by the high pressure compression assembly 130. [73] The inner passage 180 is connected to cause middle pressure refrigerant to flow from the low pressure cylinder 121 to the high pressure cylinder 131 by way of the middle pressure dscharge hole 127 of the low pressure cylinder 121, the middle pressure chamber P , the middle pressure communication hole 161a of the lower m bearing 161, the middle pressure communication hole 120a of the low pressure cylinder 121, the middle pressure communication hole 140a of the middle plate 140, and the middle pressure inflow groove 130a of the high pressure cylinder 131. Here, the middle pressure chamber P may be replaced by a pipe or may be omitted. m

[74] That is, the refrigerant compressed by the low pressure compression assembly 120 is discharged to the middle pressure chamber P formed below the low pressure m cylinder 121 through the middle pressure dscharge hole 127 formed in the low pressure cylinder 121. The middle pressure chamber P is defined by the lower bearing m

161 and the lower cover 171. In addtion, the middle pressure dscharge hole 16 Ih is formed in the lower bearing 161 to overlap with the middle pressure dscharge hole 127 of the low pressure cylinder 121. Moreover, a valve 191 for opening and closing the middle pressure dscharge hole 161h is installed on the lower bearing 161. The valve 191 opens the middle pressure dscharge hole 127 of the low pressure cylinder 121 and the middle pressure dscharge hole 16 Ih of the lower bearing 161 over a set pressure. Middle pressure refrigerant dscharged to the middle pressure chamber P m due to opening of the valve 191 is introduced into the inner space of the high pressure cylinder 131 through the middle pressure communication hole 161a of the lower bearing 161, the middle pressure communication hole 120a of the low pressure cylinder 121, the middle pressure communication hole 140a of the middle plate 140 and the middle pressure inflow groove 130a of the high pressure cylinder 131. Here, the injection tube 153 is connected to the middle pressure communication hole 120a of the low pressure cylinder 121 so as to inject gaseous refrigerant separated in the phase separator 500 into the inner passage 180. Refrigerant separated in the phase separator 500 has a higher pressure than refrigerant passing through the evaporator 400. Therefore, when the refrigerant separated in the phase separator 500 is introduced into the high pressure compression assembly 130 with the refrigerant compressed in the low pressure compression assembly 120, compressed and dscharged, input power of the compressor 200 can be reduced. [75] The refrigerant separated in the phase separator 500 and the refrigerant compressed

in the low pressure compression assembly 120 are introduced into the high pressure cylinder 131 through the middle pressure inflow groove 130a of the high pressure cylinder 131, and compressed to a high pressure by the high pressure compression assembly 130 in the same operation principle as that of the low pressure compression assembly 120. The refrigerant compressed to a high pressure in the high pressure compression assembly 130 is discharged to a discharge space D defined between the upper bearing 162 and the upper cover 172 through a high pressure discharge hole 137 of the high pressure cylinder 131 and a high pressure discharge hole 162h of the upper bearing 162. Here, a valve 192 is installed on the upper bearing 162 to open and close the high pressure discharge hole 137 of the high pressure cylinder 131 and the high pressure discharge hole 162h of the upper bearing 162. Accordingly, only when refrigerant is compressed in the high pressure compression assembly 130 over a predetermined pressure, the valve 192 opens the high pressure discharge hole 137 of the high pressure cylinder 131 and the high pressure discharge hole 162h of the upper bearing 162, thereby discharging refrigerant to the discharge space D. High pressure refrigerant is temporarily stored in the discharge space D, and then discharged to the top of the hermetic container 101 through the discharge port 172p of the upper cover 172. The high pressure refrigerant is filled in the hermetic container 101. The high pressure refrigerant filled in the hermetic container 101 is discharged to the outside through the discharge tube 152 passing through the upper portion of the hermetic container 101, circulated in the freezing cycle, introduced into the compressor 100 again through the accumulator 200 and the phase separator 500, and compressed in the compressor 100.

[76] Moreover, lubrication oil for lubricating the compression assembly 105 is filled in the lower portion of the hermetic container 101. The lubrication oil is lifted along the inside of the rotation axis 113 due to the rotation of the stirrer 103b inserted into the rotation axis 113, and supplied to the low pressure compression assembly 120 and the high pressure compression assembly 130 through the oil communication holes 103a formed in the rotation axis 113 to lubricate the compression assembly 105. Further, the oil may be supplied to the low pressure compression assembly 120 and the high pressure compression assembly 130 through the vane holes 124h and 134h formed in the low pressure cylinder 121 and the high pressure cylinder 131 to lubricate the compression assembly 105.