Hermetic Compressor with Cylinder Having Elliptical Inner Circumferential Surface, Roller, and at Least One Vane

CROSS-REFERENCE TO RELATED APPLICATION

(S) Pursuant to 35 U.S.C. § 119(a), this This application is a Reissue Application of U.S. Pat. No. 10,767,649 issued Sep. 8, 2020 (U.S. patent application Ser. No. 15/855,091 filed Dec. 27, 2017), which claims the benefit of an earlier filing date of and the right of priority to Korean Application No. 10-2016-0182836, filed in Korea on Dec. 29, 2016, the contents of which are incorporated by reference herein in its entirety.

BACKGROUND

1. Field A hermetic compressor, and more particularly, to a vane rotary compressor is disclosed herein. 2. Background Generally, a rotary compressor is a compressor having a structure in which a roller and a vane contact each other, and a compression space of a cylinder is divided into a suction chamber and a discharge chamber on the basis of by the vane. In such a general rotary compressor (hereinafter referred to as a “rotary compressor”), a the vane performs a linear motion while a the roller performs an orbiting motion, and a refrigerant is suctioned, compressed, and discharged as a volumes of the suction chamber and a the discharge chamber form a compression chamber having its volume are changed. Contrary to such a rotary compressor, there is a vane rotary compressor having a structure in which a vane inserted into a roller performs a rotary motion together with the roller, and a structure in which a compression chamber is formed as the vane is withdrawn by a centrifugal force and a back pressure. In such a vane rotary compressor, a plurality of vanes is rotated together with a roller, and the vanes slide as front end surfaces thereof contact an inner circumferential surface of a cylinder. This may cause a frictional loss to be increased in comparison to a general rotary compressor. Such a vane rotary compressor may be formed such that an inner circumferential surface of a cylinder may have a circular shape. However, recently, a vane rotary compressor having a hybrid cylinder (hereinafter, referred to as a “hybrid rotary compressor”) has been introduced, capable of reducing a frictional loss and enhancing a compression efficiency as an inner circumferential surface of a cylinder has an elliptical shape or a combination shape of an ellipse and a circle. FIG. 1 is a cross-sectional view of a compression part of a vane rotary compressor in accordance with the conventional art. FIG. 2 is a schematic view for explaining a shape of an inner circumferential surface of a hybrid cylinder in the compression part of FIG. 1 . As shown, the conventional hybrid cylinder is formed as a symmetrical elliptical cylinder an inner circumferential surface of which is symmetrical on the basis of with respect to a first center line (L 1 ) passing through a neighboring position between an inner circumferential surface of the cylinder 1 and an outer circumferential surface of a roller 2 (hereinafter, referred to as a “first contact refrence point” (P 1 )) and passing through a lateral center (Oc) of an inner space of the cylinder 1 , and on the basis of with respect to a second center line (L 2 ) perpendicular to the first center line (L 1 ) and passing through the lateral center (Oc) of the inner space of the cylinder 1 . That is, as shown in FIG. 2 , the inner circumferential surface of the cylinder 1 includes a first ellipse segment 1 a which is at an upper side on the basis of with respect to the first center line (L 1 ), and a second ellipse segment 1 b which is at a lower side on the basis of with respect to the first center line (L 1 ). The first ellipse segment 1 a has a symmetrical shape on the basis of with respect to the second center line (L 2 ), and the second ellipse segment 1 b has a symmetrical shape on the basis of with respect to the second center line (L 2 ). The roller 2 is eccentric from the lateral center (Oc) of the inner space of the cylinder 1 , and a center (Or) of the roller 2 is concentric with a center (Os) of a rotary shaft 3 . Accordingly, even while the roller 2 is being rotated, the contact reference point (P 1 ) between the cylinder 1 and the roller 2 is maintained at a same position. An outer circumferential surface of the roller 2 has a circular shape, and a plurality of vane slots 21 is formed on the outer circumferential surface of the roller 2 in a circumferential direction. As vanes 4 are slidably inserted into the vane slots 21 , a compression space 11 of the cylinder 1 is divided into a plurality of compression chambers 11 a, 11 b, 11 c. Back pressure chambers 22 that pressurize the vanes 4 towards the inner circumferential surface of the cylinder 1 by introducing oil (or a refrigerant) towards rear surfaces of the vanes 4 are formed at inner ends of the vane slots 21 corresponding to the rear surfaces of the vanes 4 . Accordingly, if the roller 2 is rotated, the vanes 4 are withdrawn from the roller 2 by a centrifugal force and a back pressure to contact the inner circumferential surface of the cylinder 1 at a contact reference point (P 2 ). The contact reference point (P 2 ) between the vanes 4 and the cylinder 1 moves along the inner circumferential surface of the cylinder 1 . On the basis of With respect to the first contact reference point (P 1 ) between the cylinder 1 and the roller 2 , a suction opening 12 is formed at one side of the inner circumferential surface of the cylinder 1 , and discharge openings 13 a, 13 b are formed at another side thereof. The vane rotary compressor has an over-compression because its compression period is shorter than that of a general rotary compressor. Due to the over-compression, a compression loss occurs. Accordingly, in the conventional cylinder 1 , in order to solve such over-compression, a compressed refrigerant is partially and sequentially discharged through a plurality of discharge openings 13 a, 13 b formed along a compression path (a compression direction). The discharge openings 13 a, 13 b may include a sub discharge opening 13 a (or a first discharge opening) positioned located along the compression path at an a position upstream side on the basis of the compression path a main discharge opening 13b , and a the main discharge opening 13 b (or a second discharge opening) positioned located along the compression path at a position downstream side of the sub discharge opening 13a . Discharge valves 51 , 52 are installed outside the discharge openings 13 a, 13 b. In the conventional vane rotary compressor, as aforementioned, in order to solve over-compression, the plurality of discharge openings 13 a, 13 b is formed on the inner circumferential surface of the cylinder 1 , along the compression path. However, if the discharge opening 13 a (especially, the sub discharge opening) has a very large inner diameter, leakage may increase among the compression chambers 11 a, 11 b, 11 c. Accordingly, the inner diameter of the discharge opening 13 a cannot be sufficiently obtained, and the over-compression cannot be solved. This may lower a compression efficiency. Further, in the conventional vane rotary compressor, as the inner circumferential surface of the cylinder 1 is formed in a symmetrical shape, a volume diagram of the compression chambers cannot be variously controlled. As a result, there is a limitation in moving a suction completion time point or a compression starting time point towards the first contact reference point. Furthermore, in the conventional vane rotary compressor, a compression starting time at the compression space of the cylinder 1 is delayed, and thus, a compression period becomes short. This may increase a pressure difference between the compression chambers. As a result, refrigerant leakage between the compression chambers may be increased, and a frictional loss may be increased between the cylinder and the vanes. Also, in the conventional vane rotary compressor, as the compression starting time at the compression chambers of the cylinder 1 is delayed, a gradient of the compression period is sharply increased. This may lower a compression efficiency due to over-compression. Additionally, in the conventional vane rotary compressor, as the cylinder 1 and the roller 2 almost linearly-contact each other at the first contact reference point (P 1 ), a sealing area is reduced. This may cause refrigerant leakage between the compression chamber which forms the suction chamber, and the compression chamber which forms the discharge chamber. This may cause a suction loss or a compression loss.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described in detail with reference to the following drawings in which like reference numerals refer to like elements, and wherein: FIG. 1 is a cross-sectional view of a compression part of a vane rotary compressor in accordance with the conventional art; FIG. 2 is a schematic view for explaining a shape of an inner circumferential surface of a hybrid cylinder in the compression part of FIG. 1 ; FIG. 3 is a longitudinal sectional view of a vane rotary compressor having a hybrid cylinder according an embodiment; FIG. 4 is a cross-sectional view of a compression part applied to FIG. 3 ; FIGS. 5 A to 5 D are sectional view views showing processes to suction, compress and discharge a refrigerant in a cylinder according to an embodiment; FIG. 6 is a schematic view for explaining a shape of an inner circumferential surface of a cylinder according to an embodiment; FIGS. 7 A- 7 C shows show graphs comparing suction completion times with each other according to a shape of an ellipse which forms an inner circumferential surface of a cylinder; and FIG. 8 is an enlarged sectional view of the cylinder shown in FIG. 4 according to another embodiment.

DETAILED DESCRIPTION

Hereinafter, a vane rotary compressor according to an embodiment will be explained with reference to the attached drawings. Where possible, like reference numerals have been used to indicate like elements, and repetitive disclosure has been omitted. FIG. 3 is a longitudinal sectional view of a vane rotary compressor having a hybrid cylinder according to an embodiment. FIG. 4 is a cross-sectional view of a compression part applied to FIG. 3 . As shown in FIG. 3 , in the vane rotary compressor according to an embodiment, a motor part or motor 200 is installed in a casing 100 , and a compression part or device 300 connected to the motor part 200 by a rotary shaft 230 is installed at one side of the motor part 200 . The motor part 200 may include a stator 210 and a rotor 220 . The casing 100 may be categorized into a horizontal type or a vertical type according to an installation aspect of the compressor. The vertical type has a structure that the motor part and the compression part are disposed at upper and lower sides in an axial direction, whereas the horizontal type has a structure that the motor part and the compression part are disposed at right and left or lateral sides. The compression part 300 may include a cylinder 330 having a compression space 410 by a main bearing 310 and a sub bearing 320 installed at both sides in an axial direction. The cylinder 330 according to this embodiment may be formed such that an inner circumferential surface thereof has an elliptical shape rather than a circular shape. The cylinder 330 may be formed as a symmetrical ellipse having a pair of long and short axes, or may be formed as an asymmetrical ellipse having a plurality of pairs of long and short axes. Such a cylinder having an asymmetrical elliptical shape is called a hybrid cylinder, and this embodiment is related to a vane rotary compressor to which a hybrid cylinder is applied. As shown in FIG. 4 , the hybrid cylinder 330 according to this embodiment (hereinafter, referred to as a “cylinder”) may have an outer circumferential surface 331 formed in a circular shape. However, the . The outer circumferential surface 331 of the cylinder 330 may be formed in a non-circular shape, if it can be fixed to an inner circumferential surface of the casing 100 . The main bearing 310 or the sub bearing 320 may be fixed to the inner circumferential surface of the casing 100 , and the cylinder 330 may be coupled to the bearing fixed to the casing 100 by, for example, a bolt. An empty space portion or space which forms a compression space 333 and includes an inner circumferential surface 332 is formed at a middle part or portion of the cylinder 330 . The empty space portion is sealed by the main bearing 310 and the sub bearing 320 , thereby forming the compression space 333 . A roller 340 , which is discussed hereinafter, may be rotatably coupled to positioned in the compression space 333 . A suction opening 334 and discharge openings 335 a, 335 b may be formed at both sides of the inner circumferential surface 332 of the cylinder 330 in a circumferential direction, on the basis of a with respect to the first reference point (P1) where the inner circumferential surface 332 of the cylinder 330 and an outer circumferential surface 341 of the roller 340 almost contact each other. The suction opening 334 may be directly connected to a suction pipe 120 which penetrates the casing 100 , and the discharge openings 335 a, 335 b may be indirectly connected to a discharge pipe 130 which may be penetratingly-coupled to the casing 100 to communicate with an inner space 110 of the casing 100 . Thus, a refrigerant may be directly suctioned into the compression space 333 through the suction opening 334 . On the other hand, the compressed refrigerant may be discharged to the inner space 110 of the casing 100 through the discharge openings 335 a, 335 b, and then discharged to the discharge pipe 130 . Accordingly, the inner space 110 of the casing 100 maintains a high pressure state which forms a discharge pressure. An additional suction valve is not installed at the suction opening 334 , whereas discharge valves 336 a, 336 b that open and close the discharge openings 335 a, 335 b may be installed at the discharge openings 335 a, 335 b. The discharge valves 336 a, 336 b may be implemented as reed valves, one first ends of which may be fixed and another second ends of which may be formed as free ends. However, the discharge valves 336 a, 336 b may be variously implemented as piston valves, for example, rather than reed valves. If the discharge valves 336 a, 336 b are implemented as reed valves, valve grooves 337 a, 337 b to mount the discharge valves 336 a, 336 b may be formed on an outer circumferential surface of in the cylinder 330 and the discharge valves 336a,336b mounted in the valve grooves 337a,337b . Accordingly, as a length of the discharge openings 335 a, 335 b is minimized, a dead volume may be reduced. As shown in FIG. 4 , the valve grooves 337 a, 337 b may be formed in a triangular shape so as to obtain a flat valve seat surface. A plurality of the discharge openings 335 a, 335 b may be formed along a compression path (a compression direction). For convenience, the discharge openings 335 a, 335 b may be sorted as a sub discharge opening (or a first discharge opening) 335 a positioned located along the compression path at an a position upstream side on the basis of the compression path of a main discharge opening 335b , and a the main discharge opening (or a second discharge opening) 335 b positioned located along the compression path at a position downstream side of the sub discharge opening 335a . However, the sub discharge opening is not necessarily required, but may be selectively provided. For example, in this embodiment, if the inner circumferential surface 332 of the cylinder 330 reduces an over-compression of a refrigerant as a compression period is formed to be long, which is discussed hereinafter, the sub discharge opening may not be formed. However, in order to minimize an over-compression amount of a refrigerant to be compressed, the sub discharge opening 335 a may be formed at a front side of the main discharge opening 335 b, for example, at an upstream side of the main discharge opening 335 b on the basis of in the compression direction. The roller 340 may be rotatably provided at the compression space 333 of the cylinder 330 . The roller 340 may have a circular outer circumferential surface, and the rotary shaft 230 may be integrally coupled to a center of the roller 340 . As a result, the roller 340 has a center (Or) consistent with a center of the rotary shaft 230 , and the roller 340 is rotated around the center (Or) together with the rotary shaft 230 . The Referring to Fig. 4, along a first center line (L1), the center (Or) of the roller 340 is eccentric from a lateral center (Oc) of an inner space of the cylinder 330 , that is, a center along a short axis of an the inner space of the cylinder 330 , so that one side of the outer circumferential surface 341 of the roller 340 almost contacts the inner circumferential surface 332 of the cylinder 330 . When it is assumed that a point of the cylinder 330 to which one side of the roller 340 almost contacts is a the first contact reference point (P 1 ), the first contact rederence point (P 1 ) may be at a position corresponding to a short-axis of an ellipse formed as a point on the inner circumferential surface 332 of the cylinder 330 where the first center line (L 1 ) passing which passes through the lateral center (Oc) of the inner space of the cylinder 330 contacts intersects the inner circumferential surface 332 of the cylinder 330 . Vane slots 342 may be formed on the outer circumferential surface 341 of in the roller 340 in a circumferential direction , and vanes 351 , 352 , 353 may be slidably coupled to the vane slots 342 . The vane slots 342 may be formed in a radial direction on the basis of with respect to the center (Or) of the roller 340 . However, in this case, it is difficult to sufficiently obtain a length of the vanes. Thus, the vane slots 342 may be formed with a predetermined inclination angle in the radial direction, for obtainment of the vane length. The vanes 351 , 352 , 353 may be inclined in a reverse direction with respect to a rotational the radial direction of the roller 340 . That is, front end surfaces of the vanes 351 , 352 , 353 , which contact the inner circumferential surface 332 of the cylinder 330 , may be inclined towards the in a rotational direction of the roller 340 such that a compression starting angle may be towards the rotational direction of the roller 340 for early-start of compression. Back pressure chambers 343 for pressurizing the vanes 351 , 352 , 353 towards the inner circumferential surface 332 of the cylinder 330 by introducing oil (or a refrigerant) towards a rear side of the vanes 351 , 352 , 353 may be formed at inner ends of the vane slots 342 . The back pressure chambers 343 may be sealed by the main bearing 310 and the sub bearing 320 . The back pressure chambers 343 may independently communicate with a back pressure passage (not shown). However, the back pressure chambers 343 may communicate together with the back pressure passage. The vanes 351 , 352 , 353 may include a first vane 351 closest to the first contact point (P 1 ) on the basis of the compression direction , a second vane 352 secondly-closest to the first contact point (P 1 ) , and the third vane 353 farthest from the first contact point (P 1 ) . In this case, the The first and second vanes 351 , 352 may be spaced from each other, the second and third vanes 352 , 353 may be spaced from each other, and the third and first vanes 353 , 351 may be spaced from each other, by a same circumferential angle. Thus, when a compression chamber formed by the first and second vanes 351 , 352 is a first compression chamber 333 a, a compression chamber formed by the second and third vanes 352 , 353 is a second compression chamber 333 b, and a compression chamber formed by the third and first vanes 353 , 351 is a third compression chamber 333 c, all the compression chambers 333 a, 333 b, 333 c have a same volume at a same crank angle. The vanes 351 , 352 , 353 may be formed to have an approximate rectangular parallelepiped shape. Both ends of the vane in a lengthwise direction may include a front end surface contacting the inner circumferential surface 332 of the cylinder 330 , and a rear end surface facing the back pressure chamber. The front end surfaces of the vanes 351 , 352 , 353 may be curved so as to linearly-contact the inner circumferential surface 332 of the cylinder 330 . The rear end surfaces of the vanes 351 , 352 , 353 may be flat so as to evenly receive a back pressure by being inserted into the back pressure chambers 343 . In the vane rotary compressor having a hybrid cylinder, if power is supplied to the motor part 200 to rotate the rotor 220 of the motor part 200 and the rotary shaft 230 coupled to the rotor 220 , the roller 340 is rotated together with the rotary shaft 230 . Then, the vanes 351 , 352 , 353 are withdrawn from or inserted into the vane slots 343 by a centrifugal force generated when the roller 340 is rotated , and by a back pressure formed at a rear side of the vanes 351 , 352 , 353 . As a result, the front end surfaces of the vanes 351 , 352 , 353 contact the inner circumferential surface 332 of the cylinder 330 . Then, the compression space 333 of the cylinder 330 forms compression chambers having a same number as the vanes 351 , 352 , 353 , by the plurality of vanes 351 , 352 , 353 . Each of the compression chambers 333 a, 333 b, 333 c has its volume changed by a shape of the inner circumferential surface 332 of the cylinder 330 and an eccentric state of the roller 340 while moving along a rotation of the roller 340 . A refrigerant filled in each of the compression chambers 333 a, 333 b, 333 c is suctioned, compressed, and discharged while moving along the roller 340 and the vanes 351 , 352 , 353 . This will be explained hereinafter. FIGS. 5 A to 5 D are sectional view showing processes to suction, compress, and discharge a refrigerant in the cylinder according to an embodiment. As shown in FIG. 5 A FIGS. 5A-5B , until before the first second vane 351 352 passes through by the suction opening 334 and the second vane 352 reaches a suction completion time, a volume of the first compression chamber 333 a is continuously increased. As a result, a refrigerant is continuously introduced into the first compression chamber 333 a from the suction opening 334 . As shown in FIG. 5 B , if the second vane 352 reaches the suction completion time (or a compression starting angle), the first compression chamber 333 a is in a sealed state to move towards the discharge openings together with the roller 340 . In this process, the volume of the first compression chamber 333 a is continuously decreased. As a result, the refrigerant in the first compression chamber 333 a is gradually compressed. As shown in FIG. 5 C , if the first vane 351 passes through by the first discharge opening 335 a and the second vane 352 does not reach the first discharge opening 335 a, the first compression chamber 333 a communicates with the first discharge opening 335 a, and the first discharge valve 336 a is opened by a pressure of the first compression chamber 333 a. Then, the refrigerant in the first compression chamber 333 a is partially discharged to the inner space 110 of the casing 100 through the first discharge opening 335 a. As a result, the pressure of the first compression chamber 333 a is lowered to a predetermined value. If the first discharge opening 335 a is not provided, the refrigerant of the first compression chamber 333 a further moves towards the second discharge opening 335 b , the main discharge opening without being discharged out . As shown in FIG. 5 D , if the first vane 351 passes through the second discharge opening 335 b and the second vane 352 reaches a discharge starting angle, the second discharge valve 336 b is opened by the pressure of the first compression chamber 333 a. As a result, the refrigerant of the first compression chamber 333 a is discharged to the inner space 110 of the casing 100 through the second discharge opening 336 b 335b . The above processes are equally repeated at the second compression chamber 333 b between the second and third vanes 352 , 353 , and at the third compression chamber 333 c between the third and first vanes 353 , 351 . Accordingly, in the vane rotary compressor according to this embodiment, a discharge operation is performed three times per single rotation of the roller 340 , that is, six times if a discharge operation from the first discharge opening is included. However, if the hybrid cylinder has an inner circumferential surface formed in a symmetrical shape, a suction period is relatively long, and a compression period becomes short. This may cause a pressure difference at each compression chamber to be increased, resulting in leakage of a refrigerant to a space between the cylinder 330 and the vanes. Also, if a back pressure with respect to the vanes is increased, a frictional loss may be increased between the cylinder 330 and the vanes. Further, as the compression period becomes short, a gradient of the compression period also becomes steep. This may increase an over-compression amount, resulting in lowering a compression efficiency. The hybrid cylinder according to this embodiment may prevent or solve over-compression by lowering a pressure difference between the compression chambers and by making the compression period have a gradual gradient, by decreasing the suction period of the compression chambers and by increasing the compression period. FIG. 6 is a schematic view for explaining a shape of the inner circumferential surface of the cylinder according to an embodiment. As shown, the hybrid cylinder according to this embodiment may be formed such that an inner circumferential surface thereof may have an a hybrid elliptical shape. In this case, center points (O′,O″) of the ellipse may be spaced apart from a lateral center (Oc) of an inner space of the cylinder 330 by a predetermined gap distances , in an eccentric manner. For a reduced suction period and an increased compression period, the center points (O′,O″) of the ellipse may be positioned at a side of the suction opening 334 and the discharge openings 335 a, 335 b on the basis of with respect to a second center line (L 2 ) that extends perpendicular to a first center line (L 1 ) passing which passes through the first contact reference point (P 1 ) and the lateral center (Oc) of the inner space of the cylinder 330 . Further, if the center point (O′) of the ellipse segment where the suction opening is formed is farther from the lateral center (Oc) of the inner space of the cylinder 330 than the center point (O″) of the ellipse segment where the discharge openings are formed, between the center points (O′,O″) which constitute the inner circumferential surface 332 of the cylinder 330 , the compression starting angle may be towards the suction opening as the suction period becomes short or decrease decreases . This may be more effective to restrict an over-compression. Further, the center point (O″) of the ellipse segment where the discharge openings are formed may be closer to the center point (O′) of the ellipse segment where the suction opening is formed, or may be farther from the lateral center (Oc) of the inner space of the cylinder 330 than the center point (O′) of the ellipse . In this case, the compression period may become long or increase and the compression gradient may become gradual. This may be effective to reduce a compression loss. For example, in the cylinder according to this embodiment, it is assumed that a line passing through the first contact reference point (P 1 ) where the inner circumferential surface 332 of the cylinder 330 and the outer circumferential surface 341 of the roller 340 are closest to each other and passing through the lateral center of the inner space of the cylinder 330 , is defined as a the first center line (L 1 ). And it is assumed that a line perpendicular to the first center line (L 1 ) and passing through the lateral center of the inner space of the cylinder 330 is defined as a the second center line (L 2 ). In this case, the inner circumferential surface 332 of the cylinder 330 may have an asymmetrical shape on the basis of with respect to the first and second center lines (L 1 , L 2 ). That is, it is assumed that the inner circumferential surface 332 of the cylinder 330 includes a first ellipse segment pair (or partial hybrid ellipse) 332 a positioned at one side of the first center line (L 1 ), and a second ellipse segment pair (or partial hybrid ellipse) 332 b positioned at another side of the first center line (L 1 ). And it is assumed that the first ellipse segment pair has a the first center point (O′), and the second ellipse segment pair has a the second center point (O″). In this case, the first center point (O′) and the second center point (O″) are spaced apart from the lateral center (Oc) of the inner space of the cylinder 330 in the same direction, on the first center line (L 1 ). The first ellipse segment pair 332 a may be is formed as two ellipses ellipse segments (or partial ellipses) 332 a′, 332 a″ having a same sum of distances to two focal points for every point thereon . Center points of the The two ellipses ellipse segments 332 a′, 332 a″ are overlapped with each other to form have the same center point (O′). The ellipse segment 332 a′ is positioned at a relatively short distance from the first contact reference point (P 1 ) than compared to the ellipse segment 332 a″ positioned at a relatively long distance from the first contact reference point (P 1 ) . The ellipse segment 332a′ may be formed such that a distance between two its focal points thereon is relatively large in comparison to a distance between focal points of the ellipse segment 332a″ . That is, the first ellipse segment pair 332 a may be formed in an asymmetrical shape, on the basis of with respect a center line passing through the first center point (O′) and perpendicular to the first center line (L 1 ) (hereinafter, referred to as a “third center line L 3 ”) , even if the sum of distances to two focal points for every point thereon is the same . In this case, it is assumed that a section from the first contact reference point (P 1 ) to an intersection point between the two ellipses ellipse segments 332 a′, 332 a″, that is, the third center line (L 3 ) is defined as a first quadrant (Q 1 ), and a section from the third center line (L 3 ) to the first center line (L 1 ) in the rotational direction of the roller 340 is defined as a second quadrant (Q 2 ). The ellipse segment 332 a′ in the first quadrant (Q 1 ) and the ellipse segment 332 a″ in the second quadrant (Q 2 ) have a same length of a long axis, but have different lengths of short axes. That is, as the ellipse segment 332 a″ in the second quadrant (Q 2 ) has the longer short axis than the ellipse segment 332 a′ in the first quadrant (Q 1 ), an eccentricity of the ellipse segment 332 a′ in the first quadrant (Q 1 ) is larger than that of the ellipse segment 332 a″ in the second quadrant (Q 2 ). With such a configuration, a suction volume in the first quadrant (Q 1 ) is increased, and a suction completion time becomes short or decreases. This may allow the suction opening 334 to move towards the contact first reference point (P1) . If the suction completion time becomes short or decreases, a compression starting time becomes early, resulting in increasing a compression period. If the compression period is increased, a motor efficiency may be enhanced, and thus, a compression efficiency of the compressor may be enhanced. Further, as a linear velocity in the first quadrant (Q 1 ) and the second quadrant (Q 2 ) is reduced, a frictional loss on the inner circumferential surface 332 of the cylinder 330 corresponding to the first ellipse segment pair 332 a may be reduced. Like the first ellipse segment pair 332 a, the second ellipse segment pair 332 b may be is formed as two ellipses ellipse segements (or partial ellipses) 332 b′, 332 b″ having a same sum of distances to two focal points for every point thereon . Center points of the The two ellipses ellipse segements 332 b′, 332 b″ are overlapped with each other to form have the same center point (O′) (O″) . The ellipse segment 332b″ is positioned at a relatively short distance from the first contact reference point (P 1 ) than compared to the ellipse segment 332b′ positioned at a relatively long distance from the first contact reference point (P 1 ) , The ellipse segment 332b″ may be formed such that a distance between two its focal points thereon is relatively large in comparison to a distance between focal points of the ellipse segment 332b′ . That is, the second ellipse segment pair 332 b may be formed in an asymmetrical shape, on the basis of with respect to a center line passing through the second center point (O″) and perpendicular to the first center line (L 1 ) (hereinafter, referred to as a “fourth center line L 4 ”) , even if the sum of distances to two focal points for every point thereon is the same . In this case, it is assumed that a section from the first center line (L 1 ) to an intersection point between the two ellipses ellipse segments 332 b′, 332 b″, that is, the fourth center line (L 4 ) , in the rotational direction of the roller 340 is defined as a third quadrant (Q 3 ), and a section from the fourth center line (L 4 ) to the first contact reference point (P 1 ) in the rotational direction of the roller 340 is defined as a fourth quadrant (Q 4 ). The ellipse segment 332 b′ in the third quadrant (Q 3 ) and the ellipse segment 332 b″ in the fourth quadrant (Q 4 ) have a same length of a long axis, but have different lengths of short axes. That is, as the ellipse segment 332 b″ in the fourth quadrant (Q 4 ) has a smaller short axis than the ellipse segment 332 b′ in the third second quadrant (Q 3 ), an eccentricity of the ellipse segment 332 b′ in the third quadrant (Q 3 ) is smaller than that of the ellipse segment 332 b″ in the fourth quadrant (Q 4 ). Accordingly, as a compression gradient in the third quadrant (Q 3 ) and the fourth quadrant (Q 4 ) becomes gradual, an over-compression amount may be reduced. This may enhance a compression efficiency. Further, as a linear velocity in the third quadrant (Q 3 ) and the fourth quadrant (Q 4 ) is reduced, a frictional loss on the inner circumferential surface 332 of the cylinder 330 corresponding to the second ellipse segment pair 332 b may be reduced. FIG. 7 shows graphs comparing suction completion times with each other according to a hybrid elliptical shape of an ellipse which forms the inner circumferential surface of the cylinder. An ellipse segment with respect to each quadrant may be defined as follows. Referring to FIG. 6 , on the first ellipse segment 332 a′ in the first quadrant (Q 1 ) and the first second ellipse segment 332 a″ in the second quadrant (Q 2 ), it may be assumed that a long-axis radius dimension of the first ellipse segment pair 332 a corresponding to positioned along the third center line (L 3 ) is A, a short-axis radius dimension of the first ellipse segment 332 a′ in the first quadrant (Q 1 ) is B1, and a short-axis radius dimension of the first second ellipse segment 332 a″ in the second quadrant (Q 2 ) is B2. In this case, the short-axis radius dimension of the first ellipse 332 a segment 332a′ in the first quadrant (Q 1 ) with respect to the long-axis radius dimension of the first ellipse segment pair 332 a may satisfy a formula, 0.5≤B1/A≤0.7. And the short-axis radius dimension of the first second ellipse segment 332 a″ in the second quadrant (Q 2 ) with respect to the long-axis radius dimension of the first ellipse segment pair 332 a may satisfy a formula, 0.7≤B2/A≤0.9. On the second third ellipse segment 332 b′ in the third quadrant (Q 3 ) and the second fourth ellipse segment 332 b″ in the fourth quadrant (Q 4 ), it may be assumed that a short-axis radius dimension of the second third ellipse segment 332 b′ in the third quadrant (Q 3 ) is B3, a short-axis radius dimension of the second fourth ellipse segment 332 b″ in the fourth quadrant (Q 4 ) is B4, and a radius dimension of the cylinder 330 at along the fourth center line (L 4 ) is C. In this case, the short-axis radius dimension (B3) of the second third ellipse segment 332 b′ in the third quadrant (Q 3 ), with respect to the radius dimension C of the cylinder 330 may satisfy a formula, 1.0≤B3/C≤1.2. Further, the short-axis radius dimension (B4) of the second fourth ellipse segment 332 b″ in the fourth quadrant (Q 4 ), with respect to the radius dimension C of the cylinder 330 may satisfy a formula, 0.8≤B4/C≤1.0. Referring to FIG. 7 FIGS. 7A-7C under such conditions, when the radiuses dimensions in the respective quadrants are defined as the following examples, results are obtained as shown in the following table. TABLE 1 Reference Example Example Example Exam- Example Items Example {circle around (1)} {circle around (2)} {circle around (3)} ple {circle around (4)} {circle around (5)} Quadrant B1/ 0.7 0.6 0.5 0.7 0.7 0.5 1 A Quadrant B2/ 0.7 0.8 0.9 0.7 0.7 0.9 2 A Quadrant B3/ 1 1 1 1.1 1.2 1.2 3 C Quadrant B4/ 1 1 1 0.9 0.9 0.8 4 C That is, it was shown that suction completion times of ellipses hybrid elliptical shapes corresponding to examples {circumflex over (1)}, {circumflex over (2)} and {circumflex over (5)} are earlier than that of an ellipse elliptical shape corresponding to the reference example. Suction completion times of ellipses hybrid elliptical shapes corresponding to examples {circumflex over (3)} and {circumflex over (4)} are equal to that of the ellipse elliptical shape corresponding to the reference example. Further, it was shown that compression starting times of the ellipses hybrid elliptical shapes corresponding to the examples {circumflex over (1)}, {circumflex over (2)} and {circumflex over (5)} are earlier than that of an ellipse elliptical shape corresponding to the reference example, as the suction completion times thereof become early. Compression starting times of the ellipses hybrid elliptical shapes corresponding to the examples {circumflex over (3)} and {circumflex over (4)} are slightly earlier than that of the ellipse elliptical shape corresponding to the reference example. When the ellipses ellipse segments in the respective quadrants (Q 1 ,Q 2 ,Q 3 ,Q 4 ) which form the inner circumferential surface 332 of the cylinder 330 are defined, it may be seen that the suction starting time becomes early and thus a compression is performed early. In the aforementioned embodiments, the first center point (O′) is formed to be farther from the lateral center (Oc) of the inner space of the cylinder 330 , than the second center point (O″). However, the second center point (O″) may be formed to be farther from the lateral center (Oc) of the inner space of the cylinder 330 , than the first center point (O′). This may be selectively applied according to whether the compressor is in a cooling mode or a heating mode. As the inner circumferential surface of the cylinder is formed in an asymmetrical shape having four ellipses ellipse segments , a volume diagram may be variously controlled. As a result, a suction period and a compression period may be properly controlled to enhance a compression efficiency. Accordingly, the inner circumferential surface of the cylinder may be formed to have a larger number of ellipses ellipse segments than the aforementioned ellipses elliptical shapes . A sealing section 338 having a same curvature radius (Rc) as a curvature radius (Rr) of the roller 340 may be further formed on the inner circumferential surface 332 of the cylinder 330 including the first contact reference point (P 1 ). FIG. 8 is an enlarged sectional view of the cylinder shown in FIG. 4 according to another embodiment. That is In the embodiment of FIG. 4 , the ellipse segment 332 a′ corresponding to the first quadrant (Q 1 ) and the ellipse segment 332 b″ corresponding to the fourth quadrant (Q 4 ) are connected to each other at a region corresponding to the first contact reference point (P 1 ) among of the inner circumferential surface 332 of the cylinder 330 . However, a curvature radius (Rc) at this region is larger than a curvature radius (Rr) of the roller 340 formed by the outer circumferential surface 341 of the roller 340 , similar to the curvature radius (Rc) at other regions. Accordingly, the outer circumferential surface 341 of the roller 340 , and the inner circumferential surface 332 of the cylinder 330 linearly are almost in linear contact with each other even at the first contact reference point (P 1 ). The first compression chamber 333 a which forms a suction pressure and the third second compression chamber 333 c 333b which forms a discharge pressure are formed at both sides of the first contact reference point (P 1 ). Accordingly, a sealing force of the first contact reference point (P 1 ) should be higher than that of another region. For this, an oil film on the first contact reference point (P 1 ) should be widely formed and should be maintained stably. However, if the outer circumferential surface 341 of the roller 340 and the inner circumferential surface 332 of the cylinder 330 linearly are almost in linear contact with each other even at the first contact reference point (P 1 ), oil is not kept at the first contact reference point (P 1 ). This may cause an oil film not to be formed, thereby not sealing a space between the two compression chambers. However, as shown in FIG. 8 , if a curvature radius (Rc 1 ) of the inner circumferential surface 332 of the cylinder 330 at a sealing section 338 of the first contact reference point (P 1 ) is smaller than a curvature radius (Rc 2 ) of the inner circumferential surface 332 of the cylinder 330 at another region, and is the same as the curvature radius (Rr) of the roller 340 formed by the outer circumferential surface 341 of the roller 340 , the roller 340 and the cylinder 330 almost come into planar-contact planar contact with each other at the sealing section 338 . Then, the sealing section 338 of the first contact reference point (P) serves as a sealing section to keep a predetermined amount of oil therein. As a result, an oil film 338 a may be formed at the sealing section 338 , thereby enhancing a sealing effect between the compression chambers 333 a, 333 c 333b . Embodiments disclosed herein provide a vane rotary compressor capable of excluding a sub discharge opening except for a main discharge opening, or capable of minimizing the number of sub discharge openings or an inner diameter of the sub discharge opening and effectively reducing over-compression. Further, embodiments disclosed herein provide a vane rotary compressor capable of variously controlling a volume diagram by forming an inner circumferential surface of a cylinder in an asymmetric shape, and capable of enhancing a compression efficiency by properly changing a suction period and a compression period. Furthermore, embodiments disclosed herein provide a vane rotary compressor capable of preventing refrigerant leakage between compression chambers and capable of reducing a frictional loss between a cylinder and a vane , by reducing a . A pressure difference between the compression chambers is reduced by reducing a suction period and increasing a compression period . This is accomplished by changing a shape of an inner circumferential surface of the cylinder. Embodiments disclosed herein also provide a vane rotary compressor capable of enhancing a compression efficiency by reducing an over-compression amount by making a gradient of a compression period gradual. Embodiments disclosed herein provide a vane rotary compressor capable of preventing refrigerant leakage between a suction chamber and a discharge chamber by obtaining a wide sealing area at a region near a cylinder and a roller. Embodiments disclosed herein further provide a vane rotary compressor having a structure that an inner circumferential surface of a cylinder is formed in an elliptical shape , and a . A long axis of the cylinder is eccentrically spaced apart from a center of the cylinder by a predetermined distance. A center line in a direction of the long axis of the cylinder, perpendicular to a center line in a direction of a short axis of the cylinder may be formed in plurality in number. Embodiments disclosed herein provide a hermetic compressor that may include a cylinder having an inner circumferential surface which forms a compression chamber formed in an a hybrid elliptical shape; a roller provided to be eccentric from the inner circumferential surface of the cylinder, and configured to change a volume of the compression chamber by being rotated; and a vane formed to be withdrawn towards the inner circumferential surface of the cylinder when the roller is rotated, and configured to divide the compression chamber into a plurality of spaces. On the basis of A first center line passes through a contact first reference point where the inner circumferential surface of the cylinder and an outer circumferential surface of the roller are closest to each other, and a first center line passing and through a lateral center of an inner space of the cylinder , an . A first pair of ellipse segments are positioned at one a first side of the first center line and forming form portions of the inner circumferential surface of the cylinder may be defined as a first ellipse, a . A center point of the first pair of ellipse may be defined as segments is a first center point , an . A second pair of ellipse segments are positioned at another a second side of the first center line and forming form portions of the inner circumferential surface of the cylinder may be defined as a second ellipse, a . A center point of the second pair of ellipse may be defined as segments is a second center point . Under these assumptions , and the first center point and the second center point may be are spaced apart from the lateral center of the inner space of the cylinder. The first center point and the second center point may be positioned on the first center line. The first center point and the second center point may be positioned on the first center line, at different separation distances from the lateral center of the inner space of the cylinder. The first center point and the second center point may be positioned on a same side, on the basis of with respect to a second center line passing through the lateral center of the inner space of the cylinder and perpendicular to the first center line. The first center point may be farther from the lateral center of the cylinder than the second center point. The first ellipse may be segment pair is formed as two ellipses having a same sum of distances to two focal points for every point thereon ellipse segments . The ellipse segment positioned at a relatively short distance from the contact first reference point than compared to the ellipse segment positioned at a relatively long distance from the contact first reference point may be formed such that a distance between two its focal points thereon is relatively large. The second ellipse may be segment pair is formed as two ellipses having a same sum of distances to two focal points for every point thereon ellipse segments . The ellipse segment positioned at a relatively short distance from the contact first reference point than compared to the ellipse segment positioned at a relatively long distance from the contact first reference point is formed such that a distance between two its focal points thereon is relatively large. Each of the first ellipse segment pair and the second ellipse may be segment pair is formed as two ellipses having a same sum of distances to two focal points for every point thereon ellipse segments . The In the first ellipse segment pair, the first ellipse segment positioned at a relatively short distance from the contact first reference point than compared to the first second ellipse segment positioned at a relatively long distance from the contact first reference point may be formed such that a distance between two its focal points thereon is relatively large. The second In the second ellipse segment pair, the fourth ellipse segment positioned at a relatively short distance from the contact first reference point than compared to the second third ellipse segment positioned at a relatively long distance from the contact first reference point may be formed such that a distance between two its focal points thereon is relatively large. A line passing through the first center point in a direction perpendicular to the first center line may be defined as a third center line, and a line passing through the second center point in a direction perpendicular to the first center line may be defined as a fourth center line. A region of the first ellipse segment pair may be divided into first and second quadrants in a rotational direction of the roller by the first and third center lines, and a region of the second ellipse segment pair may be divided into third and fourth quadrants by the first and fourth center lines. The ellipses ellipse segments in the four quadrants may be formed to have different distances between two focal points thereof . The contact first reference point may be included in the first quadrant on the basis of the third center line , and a distance between two focal points of an ellipse segment in the first quadrant including the contact first reference point may be formed to be larger than that of an ellipse segment in the second quadrant. The contact first reference point may be included in the fourth quadrant on the basis of the fourth center line, and a distance between two focal points of an ellipse segment in the fourth quadrant including the contact first reference point may be formed to be larger than that of an ellipse segment in the third quadrant. A section having a same curvature radius as the roller may be further formed at a peripheral section of the inner circumferential surface of the cylinder including the contact first reference point among the inner circumferential surface of the cylinder . Embodiments disclosed herein provided a hermetic compressor that may include a cylinder having an inner circumferential surface which forms a compression chamber formed in an a hybrid elliptical shape; a roller provided to be eccentric from the inner circumferential surface of the cylinder, and configured to change a volume of the compression chamber by being rotated; and a vane formed to be withdrawn towards the inner circumferential surface of the cylinder when the roller is rotated, and configured to divide the compression chamber into a plurality of spaces. A position where the inner circumferential surface of the cylinder and an outer circumferential surface of the roller are closest to each other may be a contact the first reference point, a line passing through the contact first reference point and a lateral center of an inner space of the cylinder may be a first center line, and a line perpendicular to the first center line and passing through the lateral center of the inner space of the cylinder may be a second center line. Under the assumptions, the inner circumferential surface of the cylinder may be formed to have an asymmetrical shape on the basis of with respect to the first and second center lines. The inner circumferential surface of the cylinder may be divided into four quadrants by the first and second center lines, and the quadrants corresponding to each other among the four quadrants may be formed to be asymmetrical with each other on the basis of with respect to the second center line. The vane rotary compressor according to embodiments may have at least the following advantages. Firstly, as a compression period is formed to be long, a pressure difference between the compression chambers may be lowered, in a state that a sub discharge opening is excluded or the number of sub discharge openings or an inner diameter of the sub discharge opening is minimized. With such a configuration, the number of processes with respect to the sub discharge opening, and the number of valves for opening and closing the sub discharge openings may be reduced, resulting in lowering the fabrication costs. Further, as the inner circumferential surface of the cylinder is formed in an asymmetrical shape having three or more ellipses four partial ellipse segments , a volume diagram may be variously controlled. As a result, a suction period and a compression period may be properly controlled to enhance a compression efficiency. Furthermore, as the inner circumferential surface of the cylinder is formed such that the suction period is short and the compression period is long, over-compression in the compression chambers may be prevented or reduced. This may enhance a compression efficiency. Also, as the inner circumferential surface of the cylinder is formed such that a position of a suction completion time and a compression starting time are towards a suction opening, the compression period becomes long, and thus, a compression difference between the compression chambers is reduced. Besides, as the compression period has a gradual gradient, an over-compression amount may be reduced. Further, as a wide sealing area is obtained at a region near the cylinder and the roller, refrigerant leakage between a suction chamber and a discharge chamber may be prevented. This may reduce a suction loss or a compression loss. Further scope of applicability of embodiments will become more apparent from the detailed description given. However, it should be understood that the detailed description and specific examples, while indicating embodiments, are given by way of illustration only, since various changes and modifications within the spirit and scope will become apparent to those skilled in the art from the detailed description. As the present features may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims. It will be understood that when an element or layer is referred to as being “on” another element or layer, the element or layer can be directly on another element or layer or intervening elements or layers. In contrast, when an element is referred to as being “directly on” another element or layer, there are no intervening elements or layers present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that, although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. Spatially relative terms, such as “lower”, “upper” and the like, may be used herein for ease of description to describe the relationship of one element or feature to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “lower” relative to other elements or features would then be oriented “upper” relative the other elements or features. Thus, the exemplary term “lower” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Embodiments of the disclosure are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the disclosure. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the disclosure should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.