Compressor

Abstract

This compressor (1) comprises a cylinder having a cylinder body and a cylinder plate that closes an end part of the cylinder body, a piston (33) that reciprocates in the cylinder, a connecting rod (32) that supports the piston (33), a crankshaft that imparts rotational force to an end part of the connecting rod (32), and a crank case that rotatably supports the crankshaft. The piston (33) is a swing piston that reciprocates while swinging in the cylinder as the crankshaft rotates, the piston (33) is constituted of at least a resin of which the surface that comes into contact with the inner peripheral side of the cylinder body is wear-resistant, and the outer peripheral surface of the piston (33) is a spherical surface having a diameter smaller than the diameter of the cylinder body. A compression chamber is formed by the piston (33), the cylinder body, and the cylinder plate, a hollow part (41b) is formed between the piston (33) and the connecting rod, and an intake port for introducing gas into the compression chamber is disposed on the cylinder plate.

Description

Technical Field

[0001] The present invention relates to a compressor.Background Art

[0002] There is a known reciprocating compressor thatinhibits transfer of compression heat generated in acompression chamber to a bearing of a connecting rod byusing a gas layer provided between a disk portion of apiston and a retainer (Patent Document 1).Prior Art DocumentPatent Document

[0003] Patent Document 1: JP-2008-248812-ASummary of the InventionProblem to be Solved by the Invention

[0004] The reciprocating compressor in Patent Document 1 isprovided with a gap over the entire surface between theretainer and the disk portion of the piston. This gapserves as a passage for gas, and further via a plurality ofpassage holes, communicates with the inside of a crankcase.In this manner, a gas layer is formed between the retainerand the disk portion of the piston. Due to the gas layer,transfer of compression heat generated in the compressionchamber to the connecting rod is inhibited.

[0005] In this reciprocating compressor, a suction valveattached to the upper surface of the retainer opens tothereby allow suction of new gas having passed through thegas layer from the space of the crankcase, into a cylinderthrough suction holes.

[0006] Due to this configuration, since the gas flows fromthe crankcase side at a time of actuation of the piston, atemperature increase in the gas layer is inhibited.

[0007] However, since heat dissipated from the compressionchamber is transferred to the gas layer in the intakestructure in Patent Document 1, the temperature of the gassucked into the cylinder increases.

[0008] Accordingly, this leads to sucking of the expandedgas into the cylinder. Typically, a lower temperature ofthe sucked gas contributes to enhancement of gas compressionefficiency, thus further efficiency improvements aredemanded.

[0009] An object of the present invention is to provide acompressor with high compression efficiency.Means for Solving the Problem

[0010] The present invention includes numerous means forsolving the problem described above, and an example thereofis a compressor including: a cylinder having at least acylindrical cylinder body and a cylinder plate closing anend portion of the cylinder body; a piston that reciprocatesin the cylinder; a connecting rod that supports the piston;and a crankshaft that applies a rotational force to an endportion of the connecting rod, in which the piston is anoscillating piston that reciprocates while oscillating inthe cylinder along with rotation of the crankshaft, thepiston is configured such that at least a surface of thepiston, the surface contacting an inner-circumference sideof the cylinder body, includes a wear-resistant resin, anouter circumferential surface of the piston is a sphericalsurface, the piston, the cylinder body, and the cylinderplate form a compression chamber, a hollow portion is formedbetween the piston and the connecting rod, and an intakeport for introducing gas to the compression chamber isarranged through the cylinder plate or a side surface of theend portion of the cylinder body.Advantages of the Invention

[0011] According to the present invention, compressionefficiency can be increased by sucking gas from an intakeport provided through the cylinder plate or the side surfaceof the end portion of the cylinder body.

[0012] Problems, configuration, and advantages other thanthose described above will be made clear by the followingexplanations of embodiments.Brief Description of the Drawings

[0013] FIG. 1 is a schematic diagram of a compressoraccording to a first embodiment of the present invention.FIG. 2 is a partial cross-sectional view of acompressor body according to the first embodiment.FIG. 3A is a front view of an example ofconfiguration of a piston and a connecting rod in the firstembodiment.FIG. 3B is a rear view of the example of theconfiguration of the piston and connecting rod in the firstembodiment.FIG. 3C is a partial cross-sectional view taken alonga cutting plane line A-A in FIG. 3A in the first embodiment.FIG. 3D is a partial cross-sectional view taken alonga cutting plane line B-B in FIG. 3C in the first embodiment.FIG. 4A is a front view of an example ofconfiguration of the piston and connecting rod in a secondembodiment.FIG. 4B is a rear view of the example of theconfiguration of the piston and connecting rod in the secondembodiment.FIG. 4C is a partial cross-sectional view taken alonga cutting plane line A-A in FIG. 4A in the secondembodiment.FIG. 4D is a partial cross-sectional view taken alonga cutting plane line B-B in FIG. 4C in the secondembodiment.FIG. 5A is a partial cross-sectional view of anexample of configuration of the piston and connecting rod ina third embodiment.FIG. 5B is a perspective view of the piston includinga cooling member (cooling fins) in the third embodiment asseen from the rear side.FIG. 5C is a perspective view of the piston includinga cooling member (cooling pins) in the third embodiment asseen from the rear side.FIG. 6 is a partial cross-sectional view depicting aflow of sucked gas near a cylinder head according to thefirst embodiment.FIG. 7A is a plan view of an example of a cylinderplate in the first embodiment.FIG. 7B is a rear view of the example of the cylinderplate in the first embodiment.FIG. 8 is a partial cross-sectional view depictingflows of sucked gas and discharged gas near the cylinderhead in a modification example.Modes for Carrying Out the Invention

[0014] [First Embodiment]A first embodiment of a compressor according to thepresent invention is explained with reference to FIG. 1 toFIG. 3D.

[0015] First, overall configuration of a compressor 1according to the present embodiment is explained withreference to FIG. 1 and FIG. 2. FIG. 1 is a schematicdiagram of the compressor 1 in the first embodiment. Inaddition, FIG. 2 is a partial cross-sectional view of acompressor body 10 in the present embodiment.

[0016] The compressor 1 depicted in FIG. 1 includes thecompressor body 10, an electric motor 2 that drives thecompressor body 10, and a tank 3 for storing gas dischargedby the compressor body 10.

[0017] The compressor body 10 compresses gas such as air byusing a piston 33 that reciprocates in a cylinder. Asdepicted in FIG. 2, the compressor body 10 includes: acrankshaft 24; a crankcase 21 that supports the crankshaft24 rotatably about a rotation central axis 24a; one cylinder22 protruding vertically from the crankcase 21; a connectingrod 32 having a base end portion connected rotatably to acrank pin of the crankshaft 24; and the piston 33 fixed to atip portion of the connecting rod 32. The cylinder 22includes: a cylindrical cylinder body 25; a cylinder plate26 closing an end portion (an upper end portion) of thecylinder body 25; and a cylinder head 23.

[0018] The cylinder plate 26 is sandwiched by the cylinderhead 23 and the cylinder body 25. The piston 33, a cylinderinner wall surface 22a which is the inner circumferentialsurface of the cylinder body 25, and the cylinder plate 26form a compression chamber 22X. The cylinder plate 26 isprovided with: an intake port 26AG (see FIG. 6 and FIG. 7A)for introducing gas into the compression chamber 22X; anddischarge ports 26BG (see FIG. 7B) for discharging gascompressed in the compression chamber 22X. An intake valve26a (see FIG. 6 and FIG. 7B) is attached to the intake port26AG, and discharge valves 26b (see FIG. 7A) are attached tothe discharge ports 26BG.

[0019] In the present embodiment, the cylinder plate 26 isarranged on a side opposite to the crankshaft 24 such thatthe piston 33 is interposed between the cylinder plate 26and the crankshaft 24.

[0020] As depicted in FIG. 2, since the piston 33reciprocates while oscillating in the cylinder 22 along withrotation of the crankshaft 24, a central axis 30X of thereciprocating piston and connecting rod is generallyinclined to a central axis 22b of the cylinder.

[0021] Along with rotation of the crankshaft 24 caused bythe electric motor 2, the compressor body 10 applies arotational force to one end portion of the connecting rod32, and the piston 33 installed in the cylinder 22 showsreciprocating motion in the cylinder 22. At a suction stepin which the piston 33 moves from the top dead center towardthe bottom dead center, the compression chamber 22X isexpanded, the intake valve 26a (see FIG. 6 and FIG. 7B)provided to the cylinder plate 26 opens, and gas is suckedinto the compression chamber 22X through the intake port26AG from an intake chamber in the cylinder head 23.

[0022] FIG. 6 is a partial cross-sectional view depicting aflow of sucked gas near the cylinder plate 26 in the presentembodiment. FIG. 7A is a plan view of an example of thecylinder plate 26 in the present embodiment. FIG. 7B is arear view of the example of the cylinder plate 26 in thepresent embodiment.

[0023] As depicted in FIG. 6, FIG. 7A, and FIG. 7B, theintake valve 26a that is arranged on the cylinder plate 26,and opens and closes the intake port 26AG, and the dischargevalves 26b that are arranged on the cylinder plate 26, andopen and close the discharge ports 26BG are actuatedaccording to reciprocation of the piston 33.

[0024] At a compression step in which the piston 33 movesfrom the bottom dead center toward the top dead center, thevolume of the compression chamber 22X is shrunk, gas in thecompression chamber 22X is compressed, the discharge valves26b (see FIG. 7A) provided on the cylinder plate 26 areopened, the compressed gas is discharged to an exhaustchamber in the cylinder head 23 through the discharge ports26BG (see FIG. 7B), and the compressed gas is sent to thetank 3 through a pipe 7 (see FIG. 1) connected to theexhaust chamber.

[0025] Note that in order to simplify the explanation, theshape of the compressor in FIG. 1 and FIG. 2 is that of aone-cylinder, one-stage compressor having only one pair of apiston and a cylinder. However, the compressor 1 may haveconfiguration having a plurality of sets of pistons andcylinders that are arranged in series or radially relativeto a crankshaft.

[0026] The compressor body 10 is arranged on and fixed tothe tank 3 in a state in which the crankshaft 24 is arrangedparallel to the rotation shaft of the electric motor 2. Asdepicted in FIG. 1, a compressor pulley 4 is fixed to thecrankshaft 24. An electric motor pulley 5 is fixed to therotation shaft of the electric motor 2. The compressorpulley 4 annexed to the compressor body 10 has vanes, and,by generating wind toward the compressor body 10 along withrotation of the vanes, facilitates heat dissipation of thecompressor body 10.

[0027] A transmission belt 6 for transmitting motive powerbetween the compressor pulley 4 and the electric motorpulley 5 is wound around the compressor pulley 4 and theelectric motor pulley 5. Thereby, according to rotation ofthe electric motor 2, the crankshaft 24 of the compressorbody 10 is rotation-driven via the electric motor pulley 5,the transmission belt 6, and the compressor pulley 4, andthe compressor body 10 compresses gas.

[0028] Note that in order to simplify the explanation, thecompressor body 10 is connected with the electric motor 2via the transmission belt 6 in the configuration depicted inFIG. 1, but the connection method is not limited to this.The crankshaft 24 of the compressor body 10 and the rotationshaft of the electric motor 2 may be directly connected witheach other by using connection means such as coupling.

[0029] Next, the structure around the piston is explainedwith reference to FIG. 2. The compressor body 10 depictedin FIG. 2 uses an oscillating-piston method in which thepiston 33 is configured integrally with the connecting rod32. In this oscillating-piston method, along with rotationof the crankshaft 24, the piston 33 reciprocates whileoscillating in the cylinder 22.

[0030] Next, the piston 33 and the connecting rod 32 areexplained with reference to FIG. 3A to FIG. 3D. FIG. 3A isa front view of an example of configuration of the pistonand connecting rod in the present embodiment, FIG. 3B is arear view thereof, and FIG. 3C is a partial cross-sectionalview taken along a cutting plane line A-A in FIG. 3A. FIG.3D is a partial cross-sectional view taken along a cuttingplane line B-B in FIG. 3C.

[0031] The piston 33 depicted in FIG. 3A and FIG. 3B is acomponent separate from the connecting rod 32 that supportsthe piston 33. At least an outer circumferential surface33a that contacts the inner-circumference side of thecylinder body 25, and a cylinder-plate-26-side piston uppersurface 33c include a wear-resistant resin.

[0032] In the present embodiment, the piston 33, except fora piston insert 41 (see FIG. 3D) mentioned later, includes ahighly wear-resistant resin.

[0033] Examples of the highly wear-resistant resin materialthat can be included in the piston 33 includepolytetrafluoroethylene (Poly Tetra Fluoro Ethylene, PTFE).Furthermore, if thermal expansion rates are taken intoconsideration, examples of the resin material of the piston33 include polyphenylenesulfide (Poly Phenylene Sulfide,PPS) and the like.

[0034] In addition, the outer circumferential surface 33a ofthe piston 33 has a spherical surface with a diameter whichis slightly smaller in size than the diameter of the innercircumference side of the cylinder body 25. The center ofthe outer circumferential surface 33a having the sphericalsurface shape is an outer-circumferential-portion center 33d(see FIG. 3A and FIG. 3C). In addition, as depicted in FIG.3C, a piston protrusion 33e is formed at an outercircumferential portion of the piston 33 that is a portionlocated on a side of the connecting rod 32 and faces theconnecting rod 32, and the piston protrusion 33e forms astructure that fits to a connecting rod protrusion 32d ofthe connecting rod 32. In addition, a ring groove 33b isprovided along the outer circumference of the piston 33 onwhich the piston 33 contacts the cylinder inner wall surface22a, and a piston ring 34 is fit into the ring groove 33b.The piston ring 34 is a seal ring that seals a gap betweenthe cylinder inner wall surface 22a and the outercircumferential surface 33a of the piston 33.

[0035] Furthermore, the piston 33 is shaped in a state inwhich the piston insert 41 including a metal such as analuminum alloy is embedded inside the piston 33. The pistoninsert 41 is for preventing the piston 33 from falling offfrom the connecting rod 32 even in a case where the piston33 receives a load by being pulled up toward the cylinderhead 23 due to a reciprocation inertial force or a frictionforce. As depicted in FIG. 3D, the piston 33 has a shape inwhich an edge section 41a of the piston insert 41 bites intothe piston 33 in the circumferential direction such that thepiston 33 does not come out. Furthermore, one or morefemale screw holes 41c, two female screw holes 41c in thepresent embodiment, that open toward the side of thecrankcase 21 are formed in the piston insert 41 such thatthe piston insert 41 and the connecting rod 32 can be fixedtogether by screws. As depicted in FIG. 2, the piston 33 isfastened with (fixed to) the connecting rod 32 by screws 35that are inserted from the side of the crankcase 21 and arearranged at two locations positioned in a directionorthogonal to the crankshaft 24.

[0036] Corresponding to this, in the present embodiment, theconnecting rod 32 depicted in FIG. 3D has screw throughholes 32c for the screws 35 at locations that are on abearing surface that supports the piston 33, and coincidewith the positions of the female screw holes 41c.

[0037] As depicted in FIG. 3D, the piston insert 41according to the present embodiment has a bowl-like shapewith its bottom being on the side of the cylinder head 23.On the bearing surface of the connecting rod 32, aconnecting rod recess 32b that is recessed toward thecrankshaft 24 (the lower sides in the figures) is formed ata position corresponding to the recess at the middle of thebowl-like shape of the piston insert 41. Due to thisstructure, a hollow portion 41b is formed between the lowersurface of the piston insert 41 and the upper surface of theconnecting rod 32. The hollow portion 41b has a plane thatis located on the upper side of the piston 33, and iscovered with the piston insert 41. In the presentembodiment, the inner space of the hollow portion 41b is asealed space.

[0038] Note that, in a case where the hollow portion 41blike the one depicted in FIG. 3D is formed, the resin itselfincluded in the piston 33 inevitably receives a gas loadwhen the piston 33 reciprocates, thus some measure ispreferably taken from the perspective of maintainingstrength.

[0039] In addition, in the form depicted in FIG. 3A to FIG.3D mentioned above, the female screw holes 41c of the pistoninsert 41 are provided parallel to the direction of thecentral axis 30X of the piston and connecting rod. However,the arrangement of these components is not limited to the"arrangement in which the female screw holes 41c areparallel to the central axis 30X of the piston andconnecting rod." For example, the female screw holes canalso be arranged so as to be inclined relative to thecentral axis 30X of the piston and connecting rod.

[0040] In the present embodiment, by forming the hollowportion 41b between the piston 33 and the connecting rod 32,the mass of the reciprocating portion including the piston33 and the connecting rod 32 can be reduced. Accordingly,vibrations of the compressor body 10 resulting from areciprocation inertial force are inhibited.

[0041] Furthermore, the plane of the hollow portion 41b thatis located on the upper side of the piston 33 is coveredwith the piston insert 41. Accordingly, since the pistoninsert 41 holds the piston 33 from inside, this leads to areduction of the amount of deformation based on shrinkage ofthe piston 33 at a time of shaping, and expansion due tocompression heat at a time of operation, even in a casewhere the hollow portion 41b is formed.

[0042] In addition, undepicted inspiratory holes exposed toexternal air are provided through the crankcase 21. Theinner volume of the crankcase 21 increases and decreasesalong with reciprocation of the piston 33, and air is takenin from the outside through the inspiratory holes, andexhausted to the outside. By performing ventilation throughthe inspiratory holes in this manner, cooling of the insideof the crankcase 21 is achieved.

[0043] Note that in order to avoid suction of dust, aninspiratory filter 27 (see FIG. 2) is attached to theinspiratory holes, and external air flowing into the spaceof the crankcase 21 is filtered.

[0044] In addition, the portion joining the connecting rod32 to the piston 33 has a cross-sectional outline shapewhich is increased in size by being provided with the hollowportion 41b. The connecting rod 32 in the presentembodiment has an approximately Y-shape when seen on across-section, and it is sufficient if its angle at thecrankshaft-side root portion is in the range fromapproximately 90° to approximately 110°, with the centralaxis 30X of the piston and connecting rod being interposedtherebetween.

[0045] The connecting rod recess 32b in the presentembodiment has a mortar-like or frustum shape. However, inthis structure, in order to fix the piston 33 and theconnecting rod 32 to each other by using the screws 35, thegap between inner wall surfaces that face each other in aradial direction along which the screws 35 are installed,that is, the inner dimension of the inner space of thehollow portion 41b, is slightly narrow when the inner spaceof the hollow portion 41b is seen on a cross-section takenin the radial direction.

[0046] In this manner, the compressor 1 according to thepresent embodiment includes: the cylinder 22 having at leastthe cylindrical cylinder body 25, and the cylinder plate 26closing the end portion of the cylinder body 25; the piston33 that reciprocates in the cylinder 22; the connecting rod32 that supports the piston 33; and the crankshaft 24 thatapplies a rotational force to the end portion of theconnecting rod 32. The piston 33 is an oscillating pistonthat reciprocates while oscillating in the cylinder 22 alongwith rotation of the crankshaft 24. At least a surface ofthe piston 33 on which the piston 33 contacts the innercircumference side of the cylinder body 25 includes a we-arresistant resin. The outer circumferential surface 33a ofthe piston 33 has a spherical surface. The piston 33, thecylinder body 25, and the cylinder plate 26 form thecompression chamber 22X. The hollow portion 41b is formedbetween the piston 33 and the connecting rod 32, and theintake port 26AG for introducing gas into the compressionchamber 22X is arranged through the cylinder plate 26.

[0047] Next, advantages of the present embodiment areexplained.

[0048] The piston 33 according to the first embodiment ofthe present invention mentioned above is an oscillatingpiston that reciprocates while oscillating in the cylinder22 along with rotation of the crankshaft 24. At least theouter circumferential surface 33a of the piston 33 on whichthe piston 33 contacts the inner-circumference side of thecylinder body 25 includes a wear-resistant resin. Inaddition, the outer circumferential surface 33a of thepiston 33 has a spherical surface made of a resin with adiameter smaller than the diameter of the cylinder body 25.Alternatively, part of the spherical surface having adiameter greater than the diameter of the cylinder body 25may be the outer circumferential surface 33a of the piston33. Then, the outer circumferential surface 33a made of aresin included in the piston 33 blocks compression heatreceived by the piston upper surface 33c.

[0049] In addition, the use of a resin as a constituentmember of the piston 33 makes it possible to attain anadvantage that the piston 33 can slide smoothly in thecompressor adopting the oscillating-piston method since thegap between the outer circumferential surface 33a of thepiston 33 and the cylinder inner wall surface 22a (see FIG.2) is kept very small. In addition, it becomes possible toavoid deformation, damage, and sealability deterioration ofthe piston ring 34 that accompany an increase in theoscillation angle.

[0050] In addition, in the compressor 1 according to thepresent embodiment, by providing the hollow portion 41bbetween the piston 33 and the connecting rod 32, the mass ofthe reciprocating portion including the piston 33 and theconnecting rod 32 can be reduced. Accordingly, vibrationsof the compressor body 10 resulting from a reciprocationinertial force are inhibited.

[0051] In addition, by sucking unexpanded gas, for examplegas such as normal-temperature air, through the intake port26AG provided through the cylinder plate 26, volumetricefficiency can be enhanced. As a result, compressionefficiency can be increased.

[0052] In addition, since the connecting rod 32 according tothe present embodiment is formed in an approximately Y-shape, the connecting rod 32 has a structure that has highermechanical rigidity and is less likely to experience abreakage or the like of the connecting rod 32 accompanyingthe locking phenomenon of the reciprocating portion, ascompared to an approximately T-shaped connecting rod inconventional technologies. Accordingly, the reliability ofthe portion joining the connecting rod 32 and the piston 33in the compressor 1 can be increased.

[0053] Accordingly, the compressor 1 according to thepresent embodiment can perform operation more stably thancompressors of conventional technologies in which a portionjoining a connecting rod to a piston is a solid portion.

[0054] [Second Embodiment]A second embodiment is explained with reference toFIG. 4A to FIG. 4D. Constituent elements which are the sameas those in the first embodiment are given identicalreference characters, and explanations thereof are omitted.The same applies also to the following embodiments.

[0055] FIG. 4A is a front view of an example ofconfiguration of the piston and connecting rod in thepresent embodiment, FIG. 4B is a rear view thereof, and FIG.4C is a partial cross-sectional view taken along a cuttingplane line A-A in FIG. 4A. FIG. 4D is a partial cross-sectional view taken along a cutting plane line B-B in FIG.4C. In the first embodiment, the inner space of the hollowportion 41b is a sealed space.

[0056] In contrast to this, as depicted in FIG. 4A, FIG. 4B,and FIG. 4C, the present second embodiment is different fromthe first embodiment in that two communication holes 32e and32f establishing communication between the space of thecrankcase 21 and the hollow portion 41b are provided on theupper-end-surface side of the connecting rod 32 contactingthe hollow portion 41b.

[0057] Next, the positions, shapes, and the like of openingsof the communication hole 32e and communication hole 32f areexplained. As depicted in FIG. 4B, the shape of the openingof the communication hole 32e in the present embodiment isan approximately fan-shape, and its center point is arrangednear a root 32Y of the approximately Y-shape of theconnecting rod 32.

[0058] The arc portion of the approximately fan-shape of thecommunication hole 32e is oriented toward the piston 33. Asdepicted in FIG. 4A, the shape of the opening of thecommunication hole 32f is part of an approximatelysemicircular shape or circular shape when the piston 33 isseen from its front side.

[0059] Note that the volume of the hollow portion 41b can beset larger as long as the mechanical strength of theconnecting rod 32 having an approximately Y-shaped cross-sectional shape at the portion joining the connecting rod 32to the piston 33 can be maintained, and additionally the atleast two screw through-holes 32c can be provided. A weightreduction of the connecting rod 32 is realized correspondingto this. In addition, in order to facilitate heatdissipation by ventilation of the hollow portion 41b, theventilation holes 32e and 32f with necessary sizes arearranged on the upper-surface side of the connecting rod 32,while adjustments of the positions of the communicationholes, and the opening shapes of the communication holes aremade as appropriate according to the shape and size of theconnecting rod 32.

[0060] Accordingly, in addition to those mentioned above,several other configuration examples with a differentnumber, opening shapes, or opening directions ofcommunication holes can be conceived.

[0061] For example, the cross-sectional shape of thecommunication hole 32e may be a circle or an oval. Inaddition, the communication hole 32e is preferably arrangedso as to face the communication hole 32f with the centralaxis 30X of the piston and connecting rod being interposedtherebetween, when seen on a radial-direction cross-sectionof the piston 33.

[0062] In addition, the cross-sectional shape of thecommunication hole 32f that serves as a gas ejection portwhen the piston 33 moves downward may be a long hole or anoval. In addition, a plurality of communication holes 32fmay be arranged in the angle range of approximately 10° to30° in the radial direction of the piston 33.

[0063] Basically, in a case where the active intake of gasfrom the crankcase 21 into the inner space of the hollowportion 41b is considered, the opening planes of thecommunication hole 32e and the communication hole 32f areparticularly preferably provided such that they haveopenings in mutually different directions.

[0064] In a case where a plurality of communication holesare provided, at least one of them has preferably an openingtoward the crankshaft 24 like the communication hole 32e.Further, at least one of them has preferably an opening in aradial direction of the cylinder body 25 like thecommunication hole 32f. Furthermore, in a case where aplurality of communication holes are provided, particularlypreferably, at least one of them has an opening toward thecrankshaft 24, and additionally at least one of them has anopening in a radial direction of the cylinder body 25.

[0065] In addition, similarly to the first embodiment, thecrankcase 21 is provided with undepicted inspiratory holesexposed to external air, and the inspiratory filter 27 foravoiding suction of dust is attached to the inspiratoryholes in the present embodiment also.

[0066] As depicted in FIG. 4C, the communication hole 32eserves as an intake port for taking in gas in the crankcase21 into the hollow portion 41b when the piston 33 movesdownward. In contrast to this, the communication hole 32fserves as an ejection port for ejecting gas inside thehollow portion 41b outward when the piston 33 movesdownward.

[0067] Because of this, the communication hole 32e and thecommunication hole 32f have openings in different directionsoutward from the inner hollow portion 41b. The opening ofthe communication hole 32e that serves as a gas intake portwhen the piston 33 moves downward is an opening orientedtoward the crankshaft 24 from the hollow portion 41b. Incontrast to this, the opening of the communication hole 32fthat serves as a gas ejection port is an opening outward ina radial direction of the cylinder body 25.

[0068] In addition, also when the piston 33 moves upward, acertain flow of gas can occur between the hollow portion 41band the space outside the connecting rod 32.

[0069] Next, advantages of the present embodiment areexplained.

[0070] The piston 33 according to the present embodiment,similarly to the first embodiment, has the outercircumferential surface 33a formed of a wear-resistant resinon which the piston 33 contacts the inner-circumference sideof the cylinder body 25, and the outer circumferentialsurface 33a has a spherical surface made of a resin with adiameter smaller than the diameter of the cylinder body 25.Thereby, compression heat received by the piston uppersurface 33c is blocked by the piston 33.

[0071] Furthermore, in the compressor 1 according to thepresent embodiment, communication is established between thespace of the hollow portion 41b and the space of thecrankcase 21 by the communication hole 32f and thecommunication hole 32e.

[0072] Because of this, the hollow portion 41b is cooled bya cooling wind 42 of gas (see FIG. 4C).

[0073] Since the cooling effect is augmented by thisconfiguration, the compressor 1 according to the presentembodiment can avoid deformation of the piston ring 34, andfavorable slidability attained by the spherical outercircumferential surface 33a made of a resin enhancessealability, as compared to compressors of conventionaltechnologies in which a portion joining a connecting rod toa piston is a solid portion. Further, since a temperatureincrease in gas taken in can be avoided, volumetricefficiency is enhanced, and operation can be performed morestably. Then, compression efficiency can be increased.Furthermore, since cooling of the piston 33 makes heattransfer to the connecting rod 32 unlikely to occur, thelifetime of a bearing of the connecting rod 32 is extended.

[0074] [Third Embodiment]A third embodiment is explained with reference toFIG. 5A to FIG. 5C. The present embodiment is differentfrom the second embodiment in that a piston insert rearsurface 41d is provided further with a cooling member forfacilitating heat dissipation such that the cooling effectat the hollow portion 41b is augmented, and heat dissipationof the piston 33 can be facilitated further.

[0075] FIG. 5A is a partial cross-sectional view of anexample of configuration of the piston and connecting rod inthe present embodiment in a case where the configuration isseen on a cross-section taken along a cutting plane line A-Ain the front view depicted in FIG. 4A. A cooling member(cooling pins 41f) is provided on the piston insert rearsurface 41d of the piston 33.

[0076] FIG. 5B is a perspective view of the piston 33including the piston insert rear surface 41d provided withthe cooling fins 41e used as a cooling member, as seen fromthe rear side. In this form, the plurality of cooling fins41e are preferably installed such that their array directioncoincides with a flow of the cooling wind 42 in the innerspace of the hollow portion 41b.

[0077] FIG. 5C is a perspective view of the piston 33including the piston insert rear surface 41d provided withthe cooling pins 41f used as a cooling member, as seen fromthe rear side. The piston insert 41 is provided with alarge number of the cooling pins 41f as a cooling memberprotruding from the piston insert rear surface 41d. In thisform, a large number of the cooling pins 41f are arrayed ina staggered manner. In a case where the cooling pins 41fare used, a greater volume of gas contacts each cooling pin41f. Accordingly, the dependency of cooling efficiency onthe flow direction of gas in the inner space of the hollowportion 41b decreases.

[0078] In addition, in the present embodiment, inspiratoryholes (not depicted) installed through the crankcase 21, andthe inspiratory filter 27 for filtering are attachedsimilarly to the second embodiment.

[0079] Next, advantages of the present embodiment areexplained.

[0080] In the present embodiment also, since the outercircumferential surface 33a of the piston 33 includes aresin, compression heat generated inside the cylinder 22 isblocked by the piston 33. In addition, since the hollowportion 41b is formed between the piston 33 and theconnecting rod 32, the mass of the reciprocating portionincluding the piston 33 and the connecting rod 32 isreduced. Accordingly, vibrations of the compressor body 10resulting from a reciprocation inertial force can beameliorated.

[0081] Furthermore, in the present embodiment, the pistoninsert rear surface 41d is provided with the cooling fins41e or the cooling pins 41f as a cooling member forfacilitating heat dissipation from the piston 33. By thesecooling members, the amount of heat dissipation from thepiston insert rear surface 41d increases.

[0082] The compressor 1 according to the present embodimentis provided with, inside the piston 33, the metallic pistoninsert 41 having the female screw holes 41c, the pistoninsert 41 is fixed to the connecting rod 32 from the side ofthe crankcase 21 by the screws 35, and the hollow portion41b is formed between the piston insert 41 and theconnecting rod 32. Accordingly, the mass of thereciprocating portion including the piston 33 and theconnecting rod 32 is reduced.

[0083] The intake port 26AG that continues to thecompression chamber 22X is installed through the cylinderplate 26, and communication is established between the spaceof the hollow portion 41b and the space of the crankcase 21by the communication holes 32f and 32e. Accordingly, heatdissipation from the piston 33 is facilitated.

[0084] Furthermore, a surface of the piston insert 41 on theside of the crankcase 21, that is, the piston insert rearsurface 41d, has the cooling fins 41e or the cooling pins41f which are cooling members to facilitate heatdissipation. Accordingly, heat dissipation from the piston33 is facilitated further as compared to a case where thepiston insert 41 is not provided with a cooling member.

[0085] Accordingly, the compressor 1 according to thepresent embodiment provides a relatively longer lifetime ofa bearing of the connecting rod 32 than the secondembodiment mentioned above.

[0086] [Modification Example]A modification example is explained with reference toFIG. 8. In the present modification example, the structureof the intake valve 26a and intake ports 26AG that supplygas to the inside of the cylinder body 25 is different fromthat in the first embodiment, the second embodiment, and thethird embodiment including the intake port 26AG through thecylinder plate 26.

[0087] As depicted in FIG. 8, the cylinder plate 26 isprovided with the discharge port 26BG, and the dischargevalve 26b that opens and closes the discharge port 26BG. Acompressed gas discharged from the discharge port 26BG issent from an outlet 26BO through the external pipe 7 to thetank 3.

[0088] The supply of gas to the inside of the cylinder body25 goes through the intake ports 26AG provided through theside surface of an end portion of the cylinder body 25. Theintake valves 26a are actuated in conjunction withreciprocation of the piston 33, and a plurality of theintake ports 26AG are opened and closed.

[0089] In the present modification example, the intake ports26AG are arranged lower than the top dead center of thepiston 33 in the axial direction of the cylinder body 25.That is, since the intake ports 26AG are arranged lower thanthe uppermost portion of the piston 33 at the top deadcenter, the intake ports 26AG are not exposed to thecompression chamber 22X when the piston 33 is positioned atthe top dead center.

[0090] Next, when the piston 33 starts moving downward fromthe position of the top dead center in order to take in air,the intake ports 26AG are exposed to the cylinder inner wallsurface 22a. At this phase, gas is supplied to the insideof the compression chamber 22X from the plurality of intakeports 26AG facing each other on the cylinder inner wallsurface 22a, and collision compression of the gas occurs.In this case, expanded gas is not taken in, and volumetricefficiency of gas that has been compressed in the end isimproved further.

[0091] In this manner, in the present modification examplealso, the discharge port 26BG attached through the cylinderplate 26, and the intake ports 26AG provided through theside surface of the end portion of the cylinder body 25 arearranged on a side opposite to the crankshaft 24 with thepiston 33 interposed therebetween.

[0092] Next, advantages of the present modification exampleare explained.

[0093] In the present modification example, the intake ports26AG are arranged lower than the top dead center of thepiston 33 in the axial direction of the cylinder body 25.Accordingly, volumetric efficiency at a time of taking inand compressing external gas is enhanced further.

[0094] The mechanism for taking in and discharging airaccording to the present modification example can be used incombination with the forms of the piston and the connectingrod in the first to third embodiments mentioned above. Inthat case, even if the gas compression rate is set higher,the compressor 1 according to the present modificationexample can keep volumetric efficiency high by providing thehollow portion 41b in the piston and the connecting rod, andfacilitating heat dissipation from the hollow portion 41b onthe rear side of the piston 33. As a result, compressionefficiency is increased.

[0095] Accordingly, the compressor 1 according to thepresent modification example enhances sealability, can keepvolumetric efficiency high even if the compression rate isset high, and can be operated more stably as compared tocompressors of conventional technologies in which a portionjoining a connecting rod to a piston is a solid portion. Inaddition, since the piston 33 can be cooled efficiently, thelifetime of a bearing of the connecting rod 32 is extended.

[0096] [Others]Note that the compressor according to the presentinvention can be applied to various compressors that areincluded in compressors compressing various types of gassuch as air or a refrigerant, and that can adopt theoscillating-piston method, and the types, models, and usesof those compressors are not limited particularly. Thepresent invention is not limited to the embodimentsdescribed above, but includes various modification examples.The embodiments described above are explained in detail inorder to explain the present invention in an easy-tounderstand manner, and the present invention is notnecessarily limited to embodiments including all theconstituent elements explained.

[0097] In addition, some of the constituent elements of anembodiment can be replaced with constituent elements ofanother embodiment, and also the constituent elements of anembodiment can additionally have constituent elements ofanother embodiment. In addition, some of the constituentelements of each embodiment can additionally have otherconstituent elements, can be deleted, or can be replacedwith other constituent elements.Description of Reference Characters

[0098] 1: Compressor2: Electric motor3: Tank4: Compressor pulley5: Electric motor pulley6: Transmission belt10: Compressor body21: Crankcase22: Cylinder22a: Cylinder inner wall surface22b: Central axis of cylinder23: Cylinder head24: Crankshaft24a: Rotation central axis25: Cylinder body26: Cylinder plate26a: Intake valve26AG: Intake port26b: Discharge valve26BG: Discharge port27: Inspiratory filter30X: Central axis of piston and connecting rod32: Connecting rod32b: Connecting rod recess32c: Screw through-hole32d: Connecting rod protrusion32e: Communication hole32f: Communication hole33: Piston33a: Outer circumferential surface33b: Ring groove33c: Piston upper surface33d: Outer-circumferential-portion center33e: Piston protrusion34: Piston ring35: Screw41: Piston insert41a: Edge section41b: Hollow portion41c: Female screw hole41d: piston insert rear surface42: Cooling wind

Claims

1. A compressor comprising: a cylinder having at least a cylindrical cylinder body and a cylinder plate closing an end portion of the cylinder body; a piston that reciprocates in the cylinder; a connecting rod that supports the piston; and a crankshaft that applies a rotational force to an end portion of the connecting rod, wherein the piston is an oscillating piston that reciprocates while oscillating in the cylinder along with rotation of the crankshaft, the piston is configured such that at least a surface of the piston, the surface contacting an inner-circumference side of the cylinder body, includes a wear-resistant resin, an outer circumferential surface of the piston is a spherical surface, the piston, the cylinder body, and the cylinder plate form a compression chamber, a hollow portion is formed between the piston and the connecting rod, and an intake port for introducing gas to the compression chamber is arranged through the cylinder plate or a side surface of the end portion of the cylinder body.

2. The compressor according to claim 1, wherein a crankcase that rotatably supports the crankshaft is included, and communication between a space of the hollow portion and a space of the crankcase is established by a communication hole.

3. The compressor according to claim 2, wherein a metallic piston insert having a female screw hole is included in an inside of the piston, the piston insert is fixed to the connecting rod from a side of the crankcase by a screw, and the hollow portion is formed between the piston insert and the connecting rod.

4. The compressor according to claim 3, wherein a surface of the piston insert on the side of the crankcase has a cooling member that facilitates heat dissipation.

5. The compressor according to claim 4, wherein the cooling member is a cooling fin or a cooling pin.

6. The compressor according to claim 2, wherein a plurality of the communication holes are provided.

7. The compressor according to claim 6, wherein at least one of the communication holes has an opening toward the crankshaft.

8. The compressor according to claim 6, wherein at least one of the communication holes has an opening in a radial direction of the cylinder body.

9. The compressor according to claim 6, wherein at least one of the communication holes has an opening toward the crankshaft, and at least one of the communication holes has an opening in a radial direction of the cylinder body.

10. The compressor according to claim 1, wherein the intake port is arranged through the cylinder plate.

11. The compressor according to claim 1, wherein the intake port is arranged through the side surface of the end portion of the cylinder body.