A hermetic compressor may include a cylinder having anellipticalinner circumferential surface; a roller eccentric from the inner circumferential surface; and at least one vane withdrawn towards the inner circumferential surface when the roller is rotated to divide a compressionchamberspace into compression chambers.On the basis ofA first center line passes throughacontactreferencepoint where the inner circumferential surfaceof the cylinderand an outer circumferential surfaceof the rollerare closest, a first center line passesandthrough alateralcenter ofan inner space ofthe cylinder, an. A first pair ofellipsesegments arepositioned at a first side of the first center line andformingform portions ofthe inner circumferential surfaceis a first ellipse, a. Acenter point of the firstpair ofellipsesegmentsis a first center point, an. A second pair ofellipsesegments arepositioned at a second side of the first center line andformingform portions ofthe inner circumferential surfaceis a second ellipse, a. Acenter point of the secondpair ofellipsesegmentsis a second center point, and the first center point and the second center point are spaced apart from thelateralcenterof the inner space of the cylinder.
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Claim 1: . A hermetic compressor, comprising:
Claim 2: . The hermetic compressor of, wherein the first center point is farther from thelateralcenter ofthe inner space ofthe cylinder than the second center point.
Claim 3: . The hermetic compressor of, wherein the firstpair ofellipsesegmentsis formed as twoellipses having a same sum of distances to two focal points for every point thereonellipse segments, and wherein an ellipsesegmentof the twoellipsesellipse segmentspositioned at a relatively short distance from thecontactreferencepointthancompared toan ellipsesegmentof the twoellipsesellipse segmentspositioned at a relatively long distance from thecontactreferencepointis formed such that a distance between two focal points thereon ishas arelativelylargelarger eccentricity.
Claim 4: . The hermetic compressor of, wherein the secondpair ofellipsesegmentsis formed as twoellipses having a same sum of distances to two focal points for every point thereonellipse segments, and wherein an ellipsesegmentof the twoellipsesellipse segmentspositioned at a relatively short distance from thecontactreferencepointthancompared toan ellipsesegmentof the twoellipsesellipse segmentspositioned at a relatively long distance from thecontactreferencepointis formed such that a distance between two focal points thereon ishas arelativelylargelarger eccentricity.
Claim 5: . The hermetic compressor of, wherein each of the firstpair ofellipsesegmentsand the secondpair ofellipsesegmentsis formed as twoellipses having a same sum of distances to two focal points for every point thereonellipse segments, whereinone of the ellipse segments ofthe firstpair ofellipsesegmentspositioned at a relatively short distance from thecontactreferencepointthancompared to another of the ellipse segments ofthe firstpair ofellipsesegmentspositioned at a relatively long distance from thecontactreferencepointis formed such that a distance between two focal points thereon ishas arelativelylargelarger eccentricity, and whereinone of the ellipse segments ofthe secondpair ofellipsesegmentspositioned at a relatively short distance from thecontactreferencepointthancompared to another of the ellipse segments ofthe secondpair ofellipsesegmentspositioned at a relatively long distance from thecontactreferencepointis formed such that a distance between two focal points thereon ishas arelativelylargelarger eccentricity.
Claim 6: . The hermetic compressor of, wherein a line passing through the first center point in a direction perpendicular to the first center line is defined as a third center line, and a line passing through the second center point in a direction perpendicular to the first center line is defined as a fourth center line, a region of the firstpair ofellipsesegmentsis divided into first and second quadrants in a rotational direction of the roller by the first and third center linessuch that the first pair of ellipse segments includes a first ellipse segment in the first quadrant and a second ellipse segment in the second quadrant, and a region of the secondpairellipsesegmentsis divided into third and fourth quadrants by the first and fourth center linessuch that the first pair of ellipse segments includes a first ellipse segment in the first quadrant and a second ellipse segment in the second quadrant, and whereineach ellipse segment oftheellipsesellipse segmentsin the four quadrantsare formed to havehas adifferent distances between two focal points thereofeccentricity.
Claim 7: . The hermetic compressor of, wherein thecontactreferencepoint is included in the first quadranton the basis of the third center line, and whereina distance between two focal pointsan eccentricityofanthe firstellipsesegmentin the first quadrantincluding the contact pointisformed to belarger thana distance between two focal pointsan eccentricityofanthe thirdellipsesegmentin the second quadrant.
Claim 8: . The hermetic compressor of, wherein thecontactreferencepoint is included in the fourth quadranton the basis of the fourth center line, and whereina distance between two focal pointsan eccentricityofanthe fourthellipsesegmentin the fourth quadrant including the contact point is formed to be larger than a distance between two focal points of an ellipse in the third quadrant.
Claim 9: . The hermetic compressor of, wherein a section having a same curvature radius as the roller is formed at a sealing section including thecontactreferencepoint along the inner circumferential surface of the cylinder.
Claim 10: . A hermetic compressor, comprising:
Claim 11: . The hemetic compressor of, where a region of the firstpair ofpartialellipseellipsesis divided into first and second quadrants in a rotational direction of the roller by the first andsecondthirdcenter lines, and a region of the secondellipsepair of partial ellipsesis divided into third and fourth quadrants by the first andthirdfourthcenter lines, and whereintheeachpartialellipsesellipsein the four quadrantsare formed to havehas adifferentdistances between two focal points thereoneccentricity.
Claim 12: . The hermetic compressor of, wherein a section having a same curvature radius as the roller is formed at a sealing section including thecontactreferencepoint along the inner circumferential surface of the cylinder.
Claim 13: 13. A hermetic compressor, comprising:
Claim 14: 14. The hermetic compressor of, wherein an eccentricity of each of the first to fourth partial ellipses is different than an eccentricity of the other partial ellipses.
Claim 15: 15. The hermetic compressor of, wherein a section having a same curvature radius as the roller is formed at a sealing section including the reference point along the inner circumferential surface of the cylinder.
Complete technical specification and implementation details from the patent document.
Pursuant to 35 U.S.C. § 119(a), thisThisapplicationis 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), whichclaimsthe benefit of an earlier filing date of and the right ofpriority 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.
A hermetic compressor, and more particularly,toa vane rotary compressor is disclosed herein.
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 chamberon the basis ofbythe vane. In such a general rotary compressor (hereinafter referred to as a “rotary compressor”),athevane performs a linear motion whileatheroller performs an orbiting motion, and a refrigerant is suctioned, compressed, and discharged asavolumes of thesuction chamber andathedischarge chamberform a compression chamber having its volumearechanged.
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.
is a cross-sectional view of a compression part of a vane rotary compressor in accordance with the conventional art.is a schematic view for explaining a shape of an inner circumferential surface of a hybrid cylinder in the compression part of.
As shown, the conventional hybrid cylinder is formed as a symmetrical elliptical cylinder an inner circumferential surface of which is symmetricalon the basis ofwith respect toa first center line (L) passing through a neighboring position between an inner circumferential surface of the cylinderand an outer circumferential surface of a roller(hereinafter, referred to as a “firstcontactrefrencepoint” (P)) and passing through alateralcenter (Oc) ofan inner space ofthe cylinder, andon the basis ofwith respect toa second center line (L) perpendicular to the first center line (L) and passing through thelateralcenter (Oc) ofthe inner space ofthe cylinder. That is, as shown in, the inner circumferential surface of the cylinderincludes a first ellipsesegmenta which is at an upper sideon the basis ofwith respect tothe first center line (L), and a second ellipsesegmentb which is at a lower sideon the basis ofwith respect tothe first center line (L). The first ellipsesegmenta has a symmetrical shapeon the basis ofwith respect tothe second center line (L), and the second ellipsesegmentb has a symmetrical shapeon the basis ofwith respect tothe second center line (L).
The rolleris eccentric from thelateralcenter (Oc) ofthe inner space ofthe cylinder, and a center (Or) of the rolleris concentric with a center (Os) of a rotary shaft. Accordingly, even while the rolleris being rotated, thecontactreferencepoint (P) between the cylinderand the rolleris maintained at a same position.
An outer circumferential surface of the rollerhas a circular shape, and a plurality of vane slotsis formed on the outer circumferential surface of the rollerin a circumferential direction. As vanesare slidably inserted into the vane slots, a compression spaceof the cylinderis divided into a plurality of compression chambersa,b,c.
Back pressure chambersthat pressurize the vanestowards the inner circumferential surface of the cylinderby introducing oil (or a refrigerant) towards rear surfaces of the vanesare formed at inner ends of the vane slotscorresponding to the rear surfaces of the vanes. Accordingly, if the rolleris rotated, the vanesare withdrawn from the rollerby a centrifugal force and a back pressure to contact the inner circumferential surface of the cylinderat acontactreferencepoint (P). Thecontactreferencepoint (P) between the vanesand the cylindermoves along the inner circumferential surface of the cylinder.
On the basis ofWith respect tothe firstcontactreferencepoint (P)between the cylinderand the roller, a suction openingis formed at one side of the inner circumferential surface of the cylinder, and discharge openingsa,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, in order to solve such over-compression, a compressed refrigerant is partially and sequentially discharged through a plurality of discharge openingsa,b formed along a compression path (a compression direction).
The discharge openingsa,b may include a sub discharge openinga (or a first discharge opening)positionedlocated along the compression pathatana positionupstreamside on the basisofthe compression patha main discharge opening 13b, andathemain discharge openingb (or a second discharge opening)positionedlocated along the compression pathat apositiondownstreamsideof the sub discharge opening 13a. Discharge valves,are installed outside the discharge openingsa,b.
In the conventional vane rotary compressor, as aforementioned, in order to solve over-compression, the plurality of discharge openingsa,b is formed on the inner circumferential surface of the cylinder, along the compression path. However, if the discharge openinga (especially, the sub discharge opening) has a very large inner diameter, leakage may increase among the compression chambersa,b,c. Accordingly, the inner diameter of the discharge openinga 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 cylinderis 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 completiontimepointor a compression startingtimepointtowards the firstcontactreferencepoint.
Furthermore, in the conventional vane rotary compressor, a compression starting time at the compression space of the cylinderis 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 cylinderis 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 cylinderand the rolleralmostlinearly-contact each other at the firstcontactreferencepoint (P), 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.
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.
is a longitudinal sectional view of a vane rotary compressor having a hybrid cylinder according to an embodiment.is a cross-sectional view of a compression part applied to.
As shown in, in the vane rotary compressor according to an embodiment, a motor part or motoris installed in a casing, and a compression part or deviceconnected to the motor partby a rotary shaftis installed at one side of the motor part. The motor partmay include a statorand a rotor. The casingmay 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 partmay include a cylinderhaving a compression spaceby a main bearingand a sub bearinginstalled at both sides in an axial direction. The cylinderaccording to this embodiment may be formed such that an inner circumferential surface thereof has an elliptical shape rather than a circular shape. The cylindermay 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, the hybrid cylinderaccording to this embodiment (hereinafter, referred to as a “cylinder”) may have an outer circumferential surfaceformed in a circular shape. However, the. Theouter circumferential surfaceof the cylindermay be formed in a non-circular shape, if it can be fixed to an inner circumferential surface of the casing. The main bearingor the sub bearingmay be fixed to the inner circumferential surface of the casing, and the cylindermay be coupled to the bearing fixed to the casingby, for example, a bolt.
An empty space portion or space which forms a compression spaceand includes an inner circumferential surfaceis formed at a middle part or portion of the cylinder. The empty space portion is sealed by the main bearingand the sub bearing, thereby forming the compression space. A roller, which is discussed hereinafter, may be rotatablycoupled topositioned inthe compression space.
A suction openingand discharge openingsa,b may be formed at both sides of the inner circumferential surfaceof the cylinderin a circumferential direction,on the basis of awith respect to the first referencepoint(P1)where the inner circumferential surfaceof the cylinderand an outer circumferential surfaceof the rolleralmost contact each other. The suction openingmay be directly connected to a suction pipewhich penetrates the casing, and the discharge openingsa,b may be indirectly connected to a discharge pipewhich may be penetratingly-coupled to the casingto communicate with an inner spaceof the casing. Thus, a refrigerant may be directly suctioned into the compression spacethrough the suction opening. On the other hand, the compressed refrigerant may be discharged to the inner spaceof the casingthrough the discharge openingsa,b, and then discharged to the discharge pipe. Accordingly, the inner spaceof the casingmaintains a high pressure state which forms a discharge pressure.
An additional suction valve is not installed at the suction opening, whereas discharge valvesa,b that open and close the discharge openingsa,b may be installed at the discharge openingsa,b. The discharge valvesa,b may be implemented as reed valves,onefirstends of which may be fixed andanothersecondends of which may be formed as free ends. However, the discharge valvesa,b may be variously implemented as piston valves, for example, rather than reed valves.
If the discharge valvesa,b are implemented as reed valves, valve groovesa,bto mount the discharge valvesa,bmay be formedon an outer circumferential surface ofinthe cylinderand the discharge valves 336a,336b mounted in the valve grooves 337a,337b. Accordingly, as a length of the discharge openingsa,b is minimized, a dead volume may be reduced. As shown in, the valve groovesa,b may be formedin a triangular shapeso as to obtain a flat valve seat surface.
A plurality of the discharge openingsa,b may be formed along a compression path (a compression direction). For convenience, the discharge openingsa,b may be sorted as a sub discharge opening (or a first discharge opening)apositionedlocated along the compression pathatana positionupstreamside on the basis of the compression pathof a main discharge opening 335b, andathemain discharge opening (or a second discharge opening)bpositionedlocated along the compression pathat apositiondownstreamsideof 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 surfaceof the cylinderreduces 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 openinga may be formed at a front side of the main discharge openingb, for example, at an upstream side of the main discharge openingbon the basis ofinthe compression direction.
The rollermay be rotatably provided at the compression spaceof the cylinder. The rollermay have a circular outer circumferential surface, and the rotary shaftmay be integrally coupled to a center of the roller. As a result, the rollerhas a center (Or) consistent with a center of the rotary shaft, and the rolleris rotated around the center (Or) together with the rotary shaft.
TheReferring to Fig. 4, along a first center line (L1), thecenter (Or) of the rolleris eccentric from alateralcenter (Oc) ofan inner space ofthe cylinder, that is, a centeralong a short axisofantheinner space of the cylinder, so that one side of the outer circumferential surfaceof the rolleralmost contacts the inner circumferential surfaceof the cylinder. When it is assumed that a point of the cylinderto which one side of the rolleralmost contacts isathefirstcontactreferencepoint (P), the firstcontactrederencepoint (P) may be at aposition corresponding to a short-axis of an ellipse formed as apoint on the inner circumferential surface 332 of the cylinder 330 where thefirst center line (L)passingwhich passes throughthelateralcenter (Oc) ofthe inner space ofthe cylindercontactsintersectsthe inner circumferential surfaceof the cylinder.
Vane slotsmay be formedon the outer circumferential surfaceofinthe rollerin a circumferential direction, and vanes,,may be slidably coupled to the vane slots. The vane slotsmay be formed in a radial directionon the basis ofwith respect tothe center (Or) of the roller. However, in this case, it is difficult to sufficiently obtain a length of the vanes. Thus, the vane slotsmay be formed with a predetermined inclination angle in the radial direction, for obtainment of the vane length.
The vanes,,may be inclinedin a reverse directionwith respecttoa rotationalthe radialdirection of the roller. That is, front end surfaces of the vanes,,, which contact the inner circumferential surfaceof the cylinder, may be inclinedtowards thein arotational direction of the rollersuch that a compression starting angle may be towards the rotational direction of the rollerfor early-start of compression.
Back pressure chambersfor pressurizing the vanes,,towards the inner circumferential surfaceof the cylinderby introducing oil (or a refrigerant) towards a rear side of the vanes,,may be formed at inner ends of the vane slots. The back pressure chambersmay be sealed by the main bearingand the sub bearing. The back pressure chambersmay independently communicate with a back pressure passage (not shown). However, the back pressure chambersmay communicate together with the back pressure passage.
The vanes,,may include a first vaneclosest to the first contact point (P) on the basis of the compression direction, a second vanesecondly-closest to the first contact point (P), and the third vanefarthest from the first contact point (P).In this case, theThefirst and second vanes,may be spaced from each other, the second and third vanes,may be spaced from each other, and the third and first vanes,may be spaced from each other, by a same circumferential angle.
Thus, when a compression chamber formed by the first and second vanes,is a first compression chambera, a compression chamber formed by the second and third vanes,is a second compression chamberb, and a compression chamber formed by the third and first vanes,is a third compression chamberc, all the compression chambersa,b,c have a same volume at a same crank angle.
The vanes,,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 surfaceof the cylinder, and a rear end surface facing the back pressure chamber.
The front end surfaces of the vanes,,may be curved so as to linearly-contact the inner circumferential surfaceof the cylinder. The rear end surfaces of the vanes,,may be flat so as to evenly receive a back pressure by being inserted into the back pressure chambers.
In the vane rotary compressor having a hybrid cylinder, if power is supplied to the motor partto rotate the rotorof the motor partand the rotary shaftcoupled to the rotor, the rolleris rotated together with the rotary shaft. Then, the vanes,,are withdrawn from or inserted into the vane slotsby a centrifugal force generatedwhen the rolleris rotated, and by a back pressure formed at a rear side of the vanes,,. As a result, the front end surfaces of the vanes,,contact the inner circumferential surfaceof the cylinder.
Then, the compression spaceof the cylinderforms compression chambers having a same number as the vanes,,, by the plurality of vanes,,. Each of the compression chambersa,b,c has its volume changed by a shape of the inner circumferential surfaceof the cylinderand an eccentric state of the rollerwhile moving along a rotation of the roller. A refrigerant filled in each of the compression chambersa,b,c is suctioned, compressed, and discharged while moving along the rollerand the vanes,,.
This will be explained hereinafter.are sectional view showing processes to suction, compress, and discharge a refrigerant in the cylinder according to an embodiment.
As shown inFIGS. 5A-5B, untilbeforethefirstsecondvane352passesthroughbythe suction openingandthe second vanereaches a suction completion time, a volume of the first compression chambera is continuously increased. As a result, a refrigerant is continuously introduced into the first compression chambera from the suction opening.
As shown in, if the second vanereaches the suction completion time (or a compression starting angle), the first compression chambera is in a sealed state to move towards the discharge openings together with the roller. In this process, the volume of the first compression chambera is continuously decreased. As a result, the refrigerant in the first compression chambera is gradually compressed.
As shown in, if the first vanepassesthroughbythe first discharge openinga and the second vanedoes not reach the first discharge openinga, the first compression chambera communicates with the first discharge openinga, and the first discharge valvea is opened by a pressure of the first compression chambera. Then, the refrigerant in the first compression chambera is partially discharged to the inner spaceof the casingthrough the first discharge openinga. As a result, the pressure of the first compression chambera is lowered to a predetermined value. If the first discharge openinga is not provided, the refrigerant of the first compression chambera further moves towards the second discharge openingb, the main discharge opening without being discharged out.
As shown in, if the first vanepasses through the second discharge openingb and the second vanereaches a discharge starting angle, the second discharge valveb is opened by the pressure of the first compression chambera. As a result, the refrigerant of the first compression chambera is discharged to the inner spaceof the casingthrough the second discharge openingb335b.
The above processes are equally repeated at the second compression chamberb between the second and third vanes,, and at the third compression chamberc between the third and first vanes,. Accordingly, in the vane rotary compressor according to this embodiment, a discharge operation is performed three times per single rotation of the roller, 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 cylinderand the vanes. Also, if a back pressure with respect to the vanes is increased, a frictional loss may be increased between the cylinderand 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.
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 haveana hybridelliptical shape. In this case, center points (O′,O″)of the ellipsemay be spaced apart from alateralcenter (Oc) ofan inner space ofthe cylinderbyapredeterminedgapdistances, in an eccentric manner. For a reduced suction period and an increased compression period, the center points (O′,O″)of the ellipsemay be positioned ata side ofthe suction openingand the discharge openingsa,bon the basis ofwith respect toa second center line (L)that extendsperpendicular to a first center line (L)passingwhich passesthrough the firstcontactreferencepoint (P) and thelateralcenter (Oc) ofthe inner space ofthe cylinder.
Further, if the center point (O′) of the ellipsesegmentwhere the suction opening is formed is farther from thelateralcenter (Oc) ofthe inner space ofthe cylinderthan the centerpoint(O″) of the ellipsesegmentwhere the discharge openings are formed,between the center points (O′,O″) which constitute the inner circumferential surfaceof the cylinder,the compression starting angle may be towards the suction opening as the suction period becomes short ordecreasedecreases. This may be more effective to restrict an over-compression. Further, the center point (O″) of the ellipsesegmentwhere the discharge openings are formed may be closer to the center point (O′) of the ellipsesegmentwhere the suction opening is formed, or may be farther from thelateralcenter (Oc) ofthe inner space ofthe cylinderthan 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.
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April 7, 2026
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