A swing-type reciprocative compressor is capable of maintaining long durability and preventing propagation of heat to the large end portion of a piston, even under high-compression. In the reciprocative compressor having a swing-type piston mechanism, a piston ring is attached to a piston ring groove to seal between a piston and a cylinder. A ring groove is provided separately from the piston ring groove on the outer circumferential side of the piston and on the crankshaft side of the piston ring groove. A guide ring restricted from moving in a radial direction and shaped like a skirt opening toward the crankshaft side is provided in the ring groove.

CLAIMS OF PRIORITY

The present application claims priority from Japanese patent application serial no. JP2009-127691, filed on May 27, 2009, the content of which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates generally to reciprocative compressors and more particularly to a swing-type reciprocative compressor in which a piston swings in a cylinder, assembly is easy and long endurance can be maintained even under high-pressure compression.

Of compressors for compressing gas, reciprocative compressors have a simple structure and allows for high-compression; therefore, they are used in various fields.

Reciprocative compressors include a piston type in which a piston is rotatably connected to a connecting rod via a bearing mechanism as illustrated in FIG. 7 of JP-A-2008-297924 and a swing type in which a piston rod is integrally combined with a compression-associated part of the upper portion of a piston as described in JP-A-2006-152960.

SUMMARY OF THE INVENTION

Reciprocative compressors are characterized by being capable of high-compression although they have small-sized and simple mechanisms. Users have increasingly requested the reciprocative compressors to achieve high-performance and high-compression.

Incidentally, the swing-type reciprocative compressor shown in JP-A-2006-152960 is configured to have a piston ring attached to the upper portion of the piston. Therefore, it has advantages of simplifying assembly and suppressing manufacturing costs. However, when a swing angle is increased along with the rotation of the piston, misalignment occurs between the center of the piston and that of the cylinder. See FIG. 6 of JP-A-2006-152960.

The piston ring is designed to have such a configuration as to accommodate such misalignment. However, for high-compression, the piston and the inner wall of the cylinder rub together, which poses a major problem of the piston ring “scoring” the cylinder.

The swing-type reciprocative compressor as described above has a simpler configuration of a compression-associated part of the piston and a less metal portion, compared with the reciprocative compressor having a piston structure as in FIG. 7 of JP-A-2008-297924. This poses a problem in that heat is easily transmitted to the large end portion (the rotary shaft side) of a piston rod portion.

Such problems are increased particularly on the high-pressure compression side of multi-stage compression.

The present invention has been made to solve such problems and aims to provide a swing-type reciprocative compressor that can maintain long durability and prevent the propagation of heat to the large end portion of a piston rod portion, even under high-compression.

A reciprocative compressor of the present invention has a swing-type piston mechanism in which a piston ring is attached to a piston ring groove to seal between a piston and a cylinder. A ring groove is provided separately from the piston ring groove on the outer circumferential side of the piston and on the crankshaft side of the piston ring groove. A guide ring restricted from moving in a radial direction is provided in the ring groove.

Preferably, the guide ring is shaped like a skirt opening toward the crankshaft side.

The reciprocative compressor according the configuration of the present invention can deal with further enhanced performance by reducing leak of compressed fluid from the piston ring. In addition, a heat insulating effect by the guide ring can be expected.

According to the present invention, a swing-type reciprocative compressor capable of maintaining long durability and preventing propagation of heat to a large end portion of a piston rod portion can be provided, even under high-compression.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments according to the present invention will hereinafter be described with reference toFIGS. 1 to 15.

First Embodiment

A first embodiment according to the present invention will hereinafter be described with reference toFIGS. 1 to 12.

A configuration of a reciprocative compression according to the first embodiment of the present invention is first described with reference toFIGS. 1 to 7.FIG. 1is a cross-sectional view of the reciprocative compressor according to the first embodiment of the present invention.FIG. 2is a cross-sectional view of the reciprocative compressor according to the first embodiment taken along line I-I ofFIG. 1.FIG. 3is an enlarged view illustrating the vicinity of an upper portion of a piston of the reciprocative compressor according to the first embodiment of the present invention.FIGS. 4A,4B and4C are views for assistance in explaining a shape of a piston ring44.FIGS. 5A and 5Bare views for assistance in explaining a shape of a guide ring43.FIG. 6is an exploded lateral view of parts in the vicinity of the upper portion of the piston.FIG. 7is an exploded perspective view illustrating a piston rod portion47and parts above the piston rod portion47.

The reciprocative compressor10sucks in gas (fluid) and compresses and discharges it. Referring toFIGS. 1 and 2, the reciprocative processor10has a crankcase11, the inside of which serves as a crank chamber12. An electric motor15is attached to the crankcase11as illustrated inFIG. 1. The electric motor15is composed of a stator16and a rotor17. The stator16is mounted to a stator holder18. The rotor17is secured to a rotor holding member21fitted to a key20attached to a key groove19. The rotor holding member21is secured to a bearing23held by a bearing holding portion22of the crankcase11and to an output shaft26supported by a bearing25held by a bearing holding portion24.

The output shaft26of the electric motor15has one end portion projecting into the crank chamber12, and a crank member29is concentrically secured to this projecting end portion. The crank member29and the output shaft26of the electric motor15constitute a crankshaft28. The output shaft26is formed with a key groove31. The crank member29is formed with a fitting hole32adapted to receive the output shaft26fitted thereinto eccentrically with respect to the outer circumferential portion. In addition, the fitting hole32is formed with a key groove33. A key34is fitted into the key grooves31,33to unite the crank member29with the output shaft26. In this way, the crankcase11supports the crankshaft28via the bearings23,25.

A balance weight37is secured to the output shaft26of the electric motor15by means of a nut38screwed to the output shaft26so as to be abutted against the crank member29at the intermediate position of the output shaft26. A cooling fan39is secured to the output shaft26at its distal end position.

A cylindrical cylinder45is mounted onto the crankcase11on the proximal end side. The cylinder45communicates with the inside of the crank chamber12on the proximal end side of its inner circumferential surface46. In addition, a cylinder head50composed of a valve seat plate48and a cylinder head body49is mounted on the distal end side of the cylinder45.

As illustrated inFIG. 2, a suction chamber51communicating with the outside and a discharge chamber52communicating with the outside are defined in the cylinder head body49.

The valve seat plate48is interposed between the cylinder45and the cylinder head body49. The valve seat plate48is formed with a suction hole57adapted to allow the suction chamber51to communicate with a compression chamber61provided on the side of the cylinder45and with a discharge hole58adapted to allow the discharge chamber52to communicate with the compression chamber61. A suction valve59and a discharge valve60which are reed valve are attached to the valve seat plate48. The suction valve59and the discharge valve60each have a proximal end side secured to the valve seat plate48with screws or the like and serving as a fixed end and a distal end side serving as a free end.

A swing-type piston63is slidably inserted and fitted into the cylinder45. The piston63includes a swing member41composed of a circular connecting portion54, a rod-like piston rod portion47and a disk-like receiving portion40; a disk-like ring holding member42; and a disk-like ring holding member56. The circular connecting portion54is rotatably connected via a bearing53to the eccentrically rotating crank member29located in the crank chamber12and at one end side of the piston63. The rod-like piston rod portion47is formed integrally with the connecting portion54to radially extend into the cylinder45. The disk-like receiving portion40is formed integrally with the piston rod portion47and provided on the side opposite the connecting portion54so as to have the center aligned with that of the piston rod portion47. The disk-like ring holding member42is coaxially screwed to the receiving portion40of the swing member41. The disk-like ring holding member56is fitted to the disk-like ring holding member42. The receiving portion40of the swing member41, the ring holding member42and the ring holding member56located on the other end side of the piston63are connected to each other and are reciprocated while swinging in the cylinder45to define the compression chamber61between the cylinder head50and the piston. Incidentally, the ring holding members42,56may be formed into a single piece.

The ring holding members42and56are screwed to the disk-like receiving portion40to define a circular piston ring groove64recessed radially inwardly, therebetween on the outer circumferential side of the piston63. Thus, the ring holding members42and56are formed with a flange portion66on the side opposite the piston rod portion47(on the side of the compression chamber61) and with a flange portion67on the side of the piston rod portion47respectively, so that the piston ring groove64is defined between the flange portions66and67. A piston ring44is attached to the piston ring groove64between both the flange portions66and67so as to seal between the piston63and the cylinder45.

The piston ring44is made of a resin material superior in wear resistance and in self-lubricating and formed generally circularly. The piston ring44is shaped in general rectangle in cross-section so as to have a radial width uniform along a generally full circle. The piston ring44is formed with a closed gap portion in a circumferential direction so that its diameter can be reduced and increased through the closed gap portion while maintaining sealing performance. Additionally, when the piston63is at the top dead center position or the bottom dead center position, its inner diameter in the state where the piston ring44is in contact with the inner circumferential surface46of the cylinder45is greater than the minimum diameter of the piston ring groove64. Thus, the piston ring44can shift in a radial direction with respect to the piston63. In addition, the piston ring44can turn relative to the piston63because of being structured not to restrict the turn.

A structure of the piston ring44is described in detail by use ofFIGS. 4A,4B and4C.FIG. 4Ais a plan view,FIG. 4Bis a lateral view andFIG. 4Cis a cross-sectional view taken along line A-A ofFIG. 4A.

The piston ring44whose shape is illustrated inFIGS. 4A to 4Cis made of a resilient resin material superior in wear resistance and in self-lubricating and generally circularly molded into a single piece. The piston ring44includes a generally circular main annular section88, a circular base section89and a circular base section90. The base section89is located at one end of the main annular section88in the circumferential direction, shifted to one end thereof in the axial direction and formed thinner than the main annular section88. The base section90is located at the other end of the main annular section88, shifted to the other end in the axial direction and formed thinner than the main annular section88. Both the base sections89and90are shifted from each other in the axial direction of the piston ring44and overlap each other in the circumferential direction, whereby mating surfaces89aand90ain contact with each other are formed. The total axial length obtained by adding the respective axial lengths of the base sections89and90together is equal to the axial length of the main annular section80.

These base sections89,90constitute the closed gap portion91. That is to say, both the base sections89and90constituting the closed gap portion91are circumferentially shifted from each other, thereby allowing for expansion and contraction of the piston ring44. The piston ring44is formed with a circumferential closed gap92between the base section89provided on the one end side of the main annular section88in the circumferential direction and the other end portion of the main annular section88in the natural state. Similarly, a closed gap93is defined between the base section90provided on the other end portion of the main annular section88and the one end portion of the main annular section88. When the piston ring44is expanded and contracted, these closed gaps92and93are enlarged and contracted.

In the present embodiment, the ring holding member42is screwed to the disk-like receiving portion40to define the circular guide ring groove65recessed radially inwardly, on the outer circumferential side of the piston. The generally disk-like guide ring43is attached to the guide ring groove65so as to secure the ring holding member42and the cylinder45centrally and coaxially with each other.FIGS. 5A and 5Billustrate a shape of the guide ring43.FIG. 5Aillustrates the guide ring43as viewed from the side of the piston rod portion47andFIG. 5Bis a cross-sectional view taken along line A-A ofFIG. 5A. The guide ring43is formed with a skirt section71adapted to increase a contact surface between the guide ring43and an inner wall surface46of the cylinder45.

Parts in the vicinity of the head of the piston to which the piston ring44and the guide ring43are attached are disassembled as illustrated inFIGS. 6 and 7. Incidentally, a tension ring44tillustrated inFIG. 7is fitted into the inside of the piston ring44to expand the piston ring44outwardly through its expanding force. Thus, the tension ring44turges the piston ring44to adhere tightly to the inner circumferential surface46of the cylinder45.

The connecting portion54is eccentrically rotated by the rotation of the crank member29, and the piston ring44and the guide ring43held by the ring holding member42are slidably guided by the inner circumferential surface46of the cylinder45. In this way, the piston63is reciprocated in the cylinder45while the ring holding members42and56swing in a direction perpendicular to the crankshaft.

The configuration of the reciprocative compressor10according to the embodiment is as described above. The operation of the compressor10is next described by use ofFIGS. 8A to 8Cin addition to the previous figures.FIG. 8Aillustrates a condition where the piston is at the top dead center.FIG. 8Billustrates a condition where the piston is at the bottom dead center.FIG. 8Cillustrates a condition where a swing angle of the piston with respect to the cylinder is maximized.

When the electric motor15is drivingly rotated, the crank member29secured to the output shaft26thereof performs eccentrically rotating movement. Then, the piston63rotatably connected to the crank member29via the bearing53allows the ring holding members42and56, the piston ring44and the guide ring43to reciprocate in the cylinder45. In a suction stroke, the ring holding member56and the piston ring44are moved toward the direction opposite the cylinder head50to enlarge the compression chamber61and to open the suction valve59with the discharge valve60remaining closed, introducing gas into the compression chamber61. In a subsequent compression stroke, the ring holding member56and the piston ring44are moved toward the cylinder head50to contract the compression chamber61and to open the discharge valve60with the suction valve59remaining closed, discharging the compressed gas from the compression chamber61into the discharge chamber52in the cylinder head50.

In the operation described above, the ring holding member56and the piston ring44reciprocate in the cylinder45while swinging.

More specifically, at the bottom dead center where the compression chamber61is most enlarged, the piston63is coaxial with the cylinder45(FIG. 8B). From this state, the crank member29is rotated counterclockwise to perform the compression stroke to move the ring holding members42,56, the piston ring44and the guide ring43in the direction of contracting the compression chamber61. Then, up to the middle between the top dead center and the bottom dead center, the connecting portion54is eccentrically rotated while being moved upward. Consequently, in the middle between the top dead center and the bottom dead center, the connecting portion54is located closest to the cylinder45(FIG. 8C). In this case, the ring holding members42,56are most tilted with respect to the central axis CA of the cylinder45.

Subsequently, in the middle of movement toward the top dead center, the ring holding members42and56generate the maximum downward force F resulting from force based on its own weight and from a centrifugal force based on swing. However, the guide ring43restricts the downward movement of the ring holding members42and56. Therefore, the piston ring groove64is maintained in the state where its center is generally coincident with the center of the cylinder45so that the piston ring44is maintained in the state where its center is generally coincident with the ring holding member42. Thereafter, at the top dead center where the compression chamber61is most contracted, the piston63becomes coaxial with the cylinder45, and thus the compression stroke is ended (FIG. 8A).

When the crank member29is rotated to perform the suction stroke from the state where the ring holding member42is at the top dead center, the piston63moves the ring holding members42and56, the piston ring44and the guide ring43in the direction of enlarging the compression chamber61. Then, up to the middle between the top dead center and the bottom dead center, the connecting portion54is eccentrically rotated while being moved downward. Consequently, the connecting portion54is located closest to the cylinder side in the middle between the top dead center and the bottom dead center. In this case, the ring holding member42is most tilted with respect to the central axis of the cylinder45.

Subsequently, the connecting portion54returns to the center as the piston63goes toward the dead bottom center. At the bottom dead center where the compression chamber is most enlarged, the piston63becomes coaxial with the cylinder45, and thus the suction stroke is ended.

According to the embodiment described above, the guide ring restricts the downward movement of the ring holding members42and56resulting from the maximum downward force F generated during the compression stroke. Therefore, the piston ring groove64is maintained in the state where its center is generally coincident with the center of the cylinder45. In this way, the piston ring44is constantly located at the center of the ring holding member42. Thus, it is possible to prevent falling-off of the piston ring44from the ring holding member42due to the pressure of compressed air, the pressure of compressed air being generated by the central misalignment between the piston ring44and the ring holding member42.

Since the guide ring43is attached and screwed to the guide ring groove65, the center of the guide ring43is coincident with that of the ring holding member42. When the cylinder45is assembled to the crankcase11, the guide ring43comes into contact with the cylinder internal wall surface46to determine the assembly position of the cylinder45. In this way, the center of the cylinder45is coincident with that of the ring holding member42. Thus, it becomes possible to perform centering between the cylinder45and the piston ring44attached onto the ring holding member42.

The guide ring43can achieve a product breakage measure which can prevent the contact between the ring holding members42,56and the cylinder45due to worn piston ring44.

Since the guide ring43is held between the ring holding member42and the receiving portion40, it is possible to prevent compression heat generated in the compression chamber61from being transmitted from the ring holding member42to the piston rod portion47. This can lower the temperature of a large end portion of the piston rod portion47. Thus, the life of the bearing53can be extended.

Various modifications of the first embodiment according to the present invention are described by use ofFIGS. 9 to 11.FIGS. 9A and 9Bare views for assistance in explaining a shape of a guide ring according to a first modification of the first embodiment.FIG. 10is an enlarged view illustrating the vicinity of an upper portion of a piston according to a second modification of the first embodiment.FIG. 11is an enlarged view illustrating the vicinity of an upper portion of a piston according to a third modification of the first embodiment.FIG. 12is an enlarged view illustrating the vicinity of an upper portion of a piston according to a fourth modification of the first embodiment.

The first modification relates to the shape of a guide ring43. Although the guide ring43of the first embodiment has the skirt section71as illustrated inFIG. 5, the guide ring43of the first modification is shaped in rectangle in cross-section as illustrated inFIG. 10by removing the skirt section71from the guide ring43.

The second modification relates to the shape of a ring holding member4and of a receiving portion40. In the second modification, the receiving portion40is formed with a step as illustrated inFIG. 10. The ring holding member42and the receiving portion40are fitted to each other so that the center of the piston rod portion47can be allowed to coincide with that of the ring holding member42.

In addition to the configuration of the second modification, the third modification is further provided with a heat-insulating air layer70between the ring holding member42and the receiving portion40. This heat-insulating air layer70can prevent heat generated by the compressed air compressed in the compression chamber61from being transmitted to the large end portion of the piston rod portion47. Thus, the life of the bearing53can be extended.

Referring toFIG. 12, a reinforcing plate95for supporting the piston ring44is provided in a fourth modification. The reinforcing plate95can support the piston ring44for prevention of its wobbling and also firmly secure the guide ring43.

Second Embodiment

A second embodiment of the present invention is hereinafter described by use ofFIGS. 13 to 15.

The compression stroke is of one-stage compression in the first embodiment; however, the compression stroke in the second embodiment is of two-stage compression.FIG. 13is a cross-sectional view of a reciprocative compressor according to the second embodiment of the present invention.FIG. 14is a cross-sectional view of the reciprocative compressor according to the second embodiment taken along line II-II ofFIG. 13.FIG. 15is an enlarged view illustrating the vicinity of an upper portion of a piston of the reciprocative compressor according to the second embodiment of the present invention.

Referring toFIG. 13, a piston73having a lip ring86is connected to an output shaft26of the reciprocative compressor of the present embodiment as well as a piston63having a piston ring44and a guide ring43attached to a piston ring groove64and a guide ring groove65, respectively, in the follow manner. A key34is fitted into a key groove74formed on the crank member75and into a key groove31formed on the output shaft26, whereby a crank member75is united with the output shaft26.

The swing-type piston73is slidably inserted and fitted into a cylinder76. The piston73includes a swing member81composed of a circular connecting portion78, a rod-like piston rod portion79and a disk-like receiving portion80; and a disk-like ring holding member82. The circular connecting portion78is rotatably connected via a bearing77to the crank member75located on one end side of the piston73and eccentrically rotated in a crank chamber12. The rod-like piston rod portion79is formed integrally with the connecting portion78to radially extend into the cylinder76. The disk-like receiving portion80is formed integrally with the piston rod portion79on the side opposite the connecting portion78so as to have the center aligned with that of the piston rod portion79. The disk-like ring holding member82is coaxially screwed to the receiving portion80of the swing member81. The receiving portion80of the swing member81located on the other end of the piston73and the ring holding member82are connected to each other and are reciprocated while swinging in the cylinder76to define a compression chamber84between the cylinder head83and the piston73. The lip ring86is attached to a lip ring groove85defined between the ring holding portion82and the receiving portion80. Incidentally, the operation of the compression stroke is the same as that described in the first embodiment.

In the present embodiment, primary compression is performed by the piston73having the lip ring86to compress air. The air thus compressed is delivered via a pipe87into the cylinder45in which secondary compression is performed by the piston63having the piston ring44and the guide ring43.FIG. 15is an enlarged view illustrating an essential portion of the piston73having the lip ring86.

According to the present embodiment described above, two-stage compression can be performed using the swing-type piston advantageous in cost for both the primary and secondary compression sides; therefore, air compression can be done effectively.

A modification of the present embodiment is next described below.

The two-stage compressor may be configured to use the piston ring44in the primary compression part.

The two-stage compressor may be configured such that both the primary compression and the second compression are performed by means of the piston63having both the piston ring44and the guide ring43. Since the piston ring44can compress higher-pressure air than the lip ring86, the configuration using the piston ring44can compress higher-pressure air in the primary compression although increasing manufacturing cost. Thus, compressor efficiency can be increased to allow for further high-pressurization as the overall compressor.