Fluid machine   

Abstract: A fluid machine includes a lubrication mechanism (70, 72) configured to utilize a rotary shaft (14) to supply lubricating oil stored in an inside bottom (2a) of a hermetic container (2) to an upper region in the hermetic container, a frame (36) secured to the hermetic container and disposed in contact with an upper surface (16a) of a cylinder block (16) to support a driven unit (6), the frame having an upper surface (38a) onto which the lubricating oil supplied to the upper region in the hermetic container flows down, a connecting rod (20) arranged under the frame and coupling the rotary shaft to a piston (18), a piston pin (66) coupling the connecting rod to the piston, a first oil feed hole (78) formed through the frame and the cylinder block, and a second oil feed hole (80) formed through the frame.

TECHNICAL FIELD

The present invention relates to fluid machines, and more particularly, to a fluid machine suitable for use as a hermetic type reciprocating compressor for compressing a carbon dioxide refrigerant.

BACKGROUND ART

As a fluid machine of this type, a hermetic type compressor has been known which is provided with a hermetic container storing lubricating oil in an inside bottom thereof, an electric motor arranged inside the hermetic container, a compression mechanism arranged inside the hermetic container and including a piston driven by the electric motor through a rotary shaft and a cylinder block having a cylinder bore formed therein, the piston being reciprocated within the cylinder bore to draw in and discharge a working fluid, and a lubrication mechanism configured to utilize centrifugal force produced by rotation of the rotary shaft, to supply the lubricating oil stored in the inside bottom of the hermetic container to an upper region in the hermetic container.

Patent Document 1 discloses a hermetic type compressor in which an oil feed hole is formed in the cylinder block to connect the cylinder bore to the outside of the cylinder bore, and an annular groove is formed in the outer peripheral surface of the piston. When the piston is at its bottom dead center, the oil feed hole communicates with the annular groove, and when the piston is at it top dead center, the oil feed hole communicates with the cylinder bore.

Patent Document 1: Japanese Laid-open Patent Publication No. 2009-197684

SUMMARY

The above conventional technique permits the lubricating oil to be effectively supplied to the piston or cylinder bore and also enables lubrication of the gap between the piston and the cylinder block. No special consideration is, however, given to localized lubrication of a connecting rod coupling the rotary shaft to the piston and of a piston pin coupling the connecting rod to the piston. Thus, there still is a demand for improvement in the lubrication performance and reliability of fluid machines.

The present invention was created in view of the above circumstances, and an object thereof is to provide a fluid machine improved in lubrication performance and reliability.

To achieve the object, the present invention provides a fluid machine comprising: a hermetic container storing lubricating oil in an inside bottom thereof; a driving unit arranged inside the hermetic container; a driven unit arranged inside the hermetic container and including a piston driven by the driving unit through a rotary shaft and a cylinder block having a cylinder bore formed therein, the piston being reciprocated within the cylinder bore to draw in and discharge a working fluid; a lubrication mechanism configured to utilize the rotary shaft to supply the lubricating oil stored in the inside bottom to an upper region in the hermetic container; a frame secured to the hermetic container and disposed in contact with an upper surface of the cylinder block to support the driven unit, the frame having an upper surface onto which the lubricating oil supplied to the upper region in the hermetic container flows down; a connecting rod arranged under the frame and coupling the rotary shaft to the piston; a piston pin coupling the connecting rod to the piston; a first oil feed hole formed through the frame and the cylinder block; and a second oil feed hole formed through the frame (claim 1).

When the piston is at a bottom dead center thereof, the first oil feed hole is located immediately above the piston pin and the second oil feed hole is located immediately above the connecting rod (claim 2).

When the piston is at a top dead center thereof, the first and second oil feed holes are located immediately above the connecting rod (claim 3).

The frame has oil reservoir sections formed by spot-facing respective openings of the first and second oil feed holes (claim 4).

The connecting rod has an oil groove formed in an upper surface thereof and extending from a location near the rotary shaft to a vicinity of the piston pin (claim 5).

Pressure of the working fluid drawn into and discharged from the driven unit prevails in an interior of the hermetic container, and the working fluid is a carbon dioxide refrigerant (claim 6). Advantageous Effects of the Invention

The fluid machine according to claim 1 is provided with the first and second oil feed holes, and the first and second oil feed holes allow the lubricating oil to reliably drop onto the piston, the piston pin and the connecting rod, which are arranged under the frame. This is because the frame is secured to the hermetic container and the lubricating oil that flows from the upper region in the hermetic container down to the upper surface of the frame is not acted upon by the centrifugal force produced by the rotation of the rotary shaft. Accordingly, the lubricating oil can effectively lubricate the driven unit without being influenced by the centrifugal force, whereby the lubrication performance and reliability of the fluid machine can be improved.

According to the invention of claim 2, when the piston is at the bottom dead center, the first oil feed hole is located immediately above the piston pin, and the second oil feed hole is located immediately above the connecting rod. Accordingly, when the piston is at the bottom dead center and thus the pressure of the working fluid in the cylinder bore is low, the lubricating oil can be made to drop from the first and second oil feed holes directly onto the piston pin and the connecting rod, respectively, without being influenced by the pressure of the working fluid slightly leaking from the cylinder bore. The driven unit can therefore be lubricated more effectively, making it possible to further improve the lubrication performance of the fluid machine.

According to the invention of claim 3, when the piston is at the top dead center, the first and second oil feed holes are located right above the connecting rod.

Thus, also when the piston is at the top dead center and thus the working fluid pressure in the cylinder bore is high, the lubricating oil can be made to drop from the first and second oil feed holes directly at least onto the connecting rod. The driven unit can therefore be lubricated more effectively, making it possible to further improve the lubrication performance of the fluid machine.

According to the invention of claim 4, the frame has the oil reservoir sections for temporarily storing the lubricating oil that flows from the upper region in the hermetic container down to the upper surface of the frame. It is therefore possible to cause the lubricating oil to intermittently drip little by little, and since the driven unit can be lubricated more effectively, the lubrication performance of the fluid machine can be further improved.

According to the invention of claim 5, the connecting rod has the oil groove formed in the upper surface thereof, and the oil groove permits the lubricating oil dropped from the first and second oil feed holes onto the connecting rod to be guided to those portions at which the connecting rod is coupled to the rotary shaft and the piston pin. Thus, since the driven unit can be lubricated more effectively, the lubrication performance of the fluid machine can be further improved.

According to the invention of claim 6, the working fluid is a carbon dioxide refrigerant. Where a carbon dioxide refrigerant is used as the working fluid, the pressure of the working fluid discharged from the cylinder bore is high, so that the pressure of the working fluid leaking from the cylinder bore and prevailing in the interior of the hermetic container may possibly become high. Consequently, the lubricating oil dropping, in particular, from the first oil feed hole directly onto the piston pin is greatly influenced by the pressure of the working fluid. With the aforementioned configuration, however, the driven unit can be effectively lubricated without the influence of the pressure of the working fluid, whereby the lubrication performance of the fluid machine can advantageously be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a compressor according to a first embodiment.

FIG. 2 is an enlarged view of a principal part of a compression mechanism shown in FIG. 1.

FIG. 3 illustrates lubrication channels in the compressor of FIG. 1.

FIG. 4 is an enlarged view of the principal part of the compression mechanism, illustrating lubrication channels formed when a piston shown in FIG. 1 is at its bottom dead center.

FIG. 5 is an enlarged view of the principal part of the compression mechanism, illustrating lubrication channels formed when the piston in FIG. 1 is at its top dead center.

FIGS. 1 through 5 illustrate a compressor 1 as a fluid machine according to a first embodiment.

The compressor 1 is a hermetic type reciprocating compressor, which is more particularly classified as displacement type compressor referred to as reciprocating compressor or piston compressor, and is used as a device constituting a refrigeration cycle, not shown, incorporated in an automatic vending machine, for example.

The refrigeration cycle has a path through which a refrigerant as a working fluid for the compressor 1 is circulated. For the refrigerant, carbon dioxide, which is a non-flammable natural refrigerant, is used, for example.

As illustrated in FIG. 1, the compressor 1 is provided with a hermetic container 2. The hermetic container 2 contains an electric motor (driving unit) 4 and a compression mechanism (driven unit) 6 to which driving force of the electric motor 4 is transmitted.

The hermetic container 2 has a shell structure constituted by a top shell 2A covering the electric motor 4 and a bottom shell 2B joined to the top shell 2A by welding and surrounding the compression mechanism 6. The electric motor 4 is housed with its longitudinal axis directed in a depth direction of the top shell 2A. The top shell 2A has a depth greater than that of the bottom shell 2B. The compression mechanism 6, on the other hand, is housed with its longitudinal axis directed in a radial direction of the bottom shell 2B. The bottom shell 2B has a smaller depth than the top shell 2A.

The electric motor 4 includes a stator 8 configured to generate a magnetic field when supplied with electric power, and a rotor 10 configured to rotate by the magnetic field generated by the stator 8. The rotor 10 is arranged inside the stator 8 coaxially therewith and is secured by shrink fitting to a main shaft section 24 of a crankshaft (rotary shaft) 14, described later. The stator 8 is supplied with electric power from outside of the compressor 1 through electric equipment 12 fixed to the hermetic container 2, and leads, not shown.

The compression mechanism 6 includes the crankshaft 14, a cylinder block 16, a piston 18, and a connecting rod 20. The crankshaft 14 has an eccentric shaft section 22 and the main shaft section 24 and is positioned perpendicularly to the connecting rod 20.

As illustrated in FIG. 2, a cylinder bore 26 is formed through the cylinder block 16. A cylinder gasket 28, a suction valve 50, described later, a valve plate 30, a head gasket 32 and a cylinder head 34 are urgingly fixed, in the mentioned order from the cylinder block side, to the cylinder block 16 by bolts, so as to close an outer open end of the cylinder bore 26.

The stator 8 shown in FIG. 1 is fixed by bolts to the cylinder block 16 with a frame 36 therebetween, and the frame 36 is secured to the hermetic container 2. The frame 36 is disposed in contact with an upper surface 16a of the cylinder block 16.

Specifically, the electric motor 4 and the compression mechanism 6 are supported by a seating section 38 forming a lower part of the frame 36, and the frame 36 is secured at the seating section 38 to the hermetic container 2. At a cylindrical section 40 forming an upper part of the frame 36, on the other hand, a bearing 42 for the main shaft section 24 is arranged on an inner peripheral surface 40a of the cylindrical section 40, and a bearing 44 for receiving thrust load of the rotor 10, such as a thrust race (bearing) or thrust washer, is arranged on an upper end face 40b of the cylindrical section 40.

As illustrated in FIG. 2, the valve plate 30 has a suction hole 46 and a discharge hole 48 for letting the refrigerant in and out, respectively. The suction and discharge holes 46 and 48 are respectively opened and closed by the suction and discharge valves 50 and 52, each constituted by a reed valve.

The cylinder head 34 has a suction chamber 54 and a discharge chamber 56, both for the refrigerant. When the discharge valve 52 is open during compression stroke of the piston 18, the discharge chamber 56 communicates with the cylinder bore 26 through the discharge hole 48. On the other hand, when the suction valve 50 is open during suction stroke of the piston 18, the suction chamber 54 communicates with the cylinder bore 26 through the suction hole 46.

A suction pipe 58 and a discharge pipe 60 are fixed to the hermetic container 2 and have one ends connected to the suction and discharge chambers 54 and 56, respectively, of the cylinder head 34. The suction and discharge pipes 58 and 60 have respective other ends connected to the refrigeration cycle via a suction muffler and a discharge muffler, respectively, neither of which is shown. The mufflers serve to reduce pulsation and noise of the refrigerant flowing between the compressor 1 and the refrigeration cycle.

The connecting rod 20 has one end formed as a large end portion 62 to which the eccentric shaft section 22 of the crankshaft 14 is rotatably coupled, and has the other end formed as a small end portion 64 to which the piston 18 is coupled so as to be capable of reciprocating motion. The small end portion 64 is coupled to the piston 18 by a piston pin 66, and a fixing pin 68 prevents the piston pin 66 from coming off the piston 18.

With the individual parts configured in this manner, as the crankshaft 14 rotates, the connecting rod 20 makes a rocking motion on the piston pin 66 as a fulcrum, in conjunction with eccentric rotation of the eccentric shaft section 22, and the piston 18 makes a reciprocating motion within the cylinder bore 26 in conjunction with the rocking motion of the connecting rod 20.

Discharge pressure of the refrigerant mainly prevails in the interior of the hermetic container 2. A small amount of lubricating oil for lubricating individual sliding parts of the electric motor 4 and compression mechanism 6, such as the bearings 42 and 44, is stored in an inside bottom 2a of the hermetic container 2.

An oil passage (lubrication mechanism) 70 is formed in the crankshaft 14 so as to extend from a nearly axial center of a lower end face 22a of the eccentric shaft section 22 up to an intermediate portion of the main shaft section 24. The oil passage 70 opens, at an upper section thereof, in an outer peripheral surface 24a of the main shaft section 24, and is connected, at a lower section thereof, with an oil pipe (lubrication mechanism) 72. The oil pipe 72 has an inclined portion 74 at a distal end portion thereof, and the inclined portion 74 is so inclined as to extend from nearly the axial center of the eccentric shaft section 22 toward the axis of the main shaft section 24. A distal end of the inclined portion 74 of the oil pipe 72 extends to an oil reservoir 76 formed in the inside bottom 2a of the hermetic container 2 and having a concave shape as viewed in section.

The oil reservoir 76 has a size and a depth such that a small amount, for example, about 200 cc, of lubricating oil can be stored with its oil level located above the distal end of the oil pipe 74. As the oil pipe 72 eccentrically rotates together with the eccentric shaft section 22 due to rotation of the crankshaft 14, centrifugal force acts upon the lubricating oil in the inclined portion 74 of the oil pipe 72 in an obliquely upward and outward direction, so that the lubricating oil is drawn from the oil reservoir 76 upward into the oil passage 74 by the centrifugal force.

Operation and function of the compressor 1 will be now described.

In the compressor 1, when electric power is supplied to the stator 8, the rotor 10, which is fixed to the main shaft section 24, and thus the crankshaft 14 rotate, with the result that the piston 18 is actuated by the connecting rod 20 to make a reciprocating motion inside the cylinder bore 26. As the piston 18 reciprocates, the refrigerant is drawn from the refrigeration cycle into the cylinder bore 26, then compressed in the cylinder bore 26, and discharged to the refrigeration cycle.

Specifically, as the piston 18 moves in a direction of decreasing the volumetric capacity of the cylinder bore 26, the refrigerant in the cylinder bore 26 is compressed, and when the pressure in the cylinder bore 26 exceeds a refrigerant discharge pressure, the discharge valve 52 opens because of the difference between the pressure in the cylinder bore 26 and the pressure in the discharge chamber 56. The compressed refrigerant is guided through the discharge hole 48 into the discharge chamber 56 and then is discharged to the refrigeration cycle through the discharge pipe 60.

Subsequently, as the piston 18 moves from its top dead center in a direction of increasing the volumetric capacity of the cylinder bore 26, the pressure in the cylinder bore 26 lowers. Since the pressure in the cylinder bore 26 lowers, the discharge valve 52 closes due to the difference between the pressure in the cylinder bore 26 and the pressure in the discharge chamber 56.

When the pressure in the cylinder bore 26 drops below a refrigerant suction pressure, the suction valve 50 opens because of the difference between the pressure in the cylinder bore 26 and the pressure in the suction chamber 54. The refrigerant in the refrigeration cycle is guided through the suction pipe 58 into the suction chamber 54 and then drawn into the cylinder bore 26 via the suction hole 46.

Then, as the piston 18 moves from its bottom dead center in a direction of decreasing the volumetric capacity of the cylinder bore 26, the refrigerant in the cylinder bore 26 is compressed. In this manner, a series of processes, namely, suction of the refrigerant from the refrigeration cycle into the cylinder bore 26, compression of the refrigerant in the cylinder bore 26 and discharge of the refrigerant to the refrigeration cycle, repeatedly takes place.

As indicated by the arrows with symbols in FIG. 3, as the compressor 1 operates in the aforementioned manner, the lubricating oil drawn upward from the oil reservoir 76 into the oil passage 70 (arrow (a)) flows out of the oil passage (arrow (b)) and then downward toward the eccentric shaft section 22 (arrow (c)), and after lubricating the large end portion 62 and its vicinities, the lubricating oil flows down by gravity to the oil reservoir 76 (arrow (d)).

On the other hand, part of the lubricating oil flowing out of the oil passage 70 moves upward due to centrifugal force along outer peripheral grooves, not shown, formed in the crankshaft 14 (arrow (e)), thus forming an oil film in the gap between the crankshaft 14 and the frame 36 to lubricate the bearing 42, and is guided toward the upper end of the crankshaft 14. On reaching the upper end face 40b of the cylindrical section 40 (arrow (f)), the lubricating oil lubricates the bearing 44, then passes through the gap between the rotor 8 and the frame 36 (arrow (g)), and flows down onto the upper surface 38a of the seating section 38 of the frame 36.

The lubricating oil on the upper surface 3Ba passes through a first oil feed hole 78 formed through the seating section 38 of the frame 36 and the cylinder block 16 (arrow (h)) and a second oil feed hole 80 formed through the seating section 38 of the frame 36 (arrow (i)), then lubricates the compression mechanism 6, and flows down to the oil reservoir 76 (arrow (d)).

Part of the lubricating oil that failed to pass through the bearing 44 moves further upward along an inner peripheral surface 10a of the rotor 10 up to the upper end of the rotor 10 (arrow (j)), is scattered outward due to the centrifugal force produced by the rotation of the rotor 10 to cool the stator 8 (arrow (k)), and passes through the gap between the stator 8 and the rotor 10 (arrow (l)) and then through the first oil feed hole 78 (arrow (h)) and the second oil feed hole 80 (arrow (i)). After lubricating the compression mechanism 6, the lubricating oil flows down to the oil reservoir 76 (arrow (d)).

The compression mechanism 6 is lubricated in the manner described below. Oil mist drawn into the cylinder bore 26 enters, together with the refrigerant gas leaking from the cylinder bore 26, the gap between the piston 18 and the cylinder block 16 for sealing and lubrication of the piston 18 (arrow (m)). Also, part of the lubricating oil drawn into the cylinder bore 26 is discharged to the discharge chamber 56 and then to the refrigeration cycle through the discharge pipe 60 (arrow (n)).

The lubricating oil is thereafter drawn from the refrigeration cycle, together with the refrigerant, into the suction chamber 54 through the suction pipe 58 (arrow (o)), then adheres to a wall surface 54a of the suction chamber 54, and flows down by gravity to the oil reservoir 76 (arrow (p)). The lubricating oil thus reaching the oil reservoir 76 is again drawn up through the oil pipe 72 and circulates in the hermetic container 2 or through the refrigeration cycle, as stated above, while contributing to sealing and lubrication of the individual sliding parts of the electric motor 4 and compression mechanism 6.

As illustrated in FIG. 4, the first oil feed hole 78 is formed in a position such that when the piston 18 is at the bottom dead center, the first oil feed hole 78 is located immediately above the piston pin 66. The lubricating oil that drips from the first oil feed hole 78 when the piston 18 is at the bottom dead center flows toward the sliding portion where the piston pin 66 is brought into sliding contact with the piston 18, as indicated by arrows, and thus can directly lubricate the piston pin 66.

The second oil feed hole 80 is formed in a position such that when the piston 18 is at the bottom dead center, the second oil feed hole 80 is located right above the connecting rod 20. The lubricating oil that drips from the second oil feed hole 80 when the piston 18 is at the bottom dead center is able to directly lubricate the connecting rod 20.

The oil feed holes 78 and 80 are respectively constituted by oil reservoir sections 82 and 84 and small-diameter holes 86 and 88 located beneath the respective oil reservoir sections 82 and 84. The lubricating oil that has reached the upper surface 38a is temporarily stored in the oil reservoir sections 82 and 84.

The oil reservoir sections 82 and 84 are formed by spot-facing the openings of the respective oil feed holes 78 and 80 in the seating section 38 of the frame 36. The oil reservoir section 82 is formed so as to extend from the seating section 38 up to an intermediate portion of the cylinder block 16.

Compared with the oil reservoir sections 82 and 84, the small-diameter holes 86 and 88 have reduced diameters set in accordance with the kinematic viscosity of the lubricating oil used. The lubricating oil stored in the oil reservoir sections 82 and 84 passes through the respective small-diameter holes 86 and 88, so that the lubricating oil intermittently drips drop by drop, or in a few drops, to the compression mechanism 6.

Also, the connecting rod 20 has an oil groove 90 formed in an upper surface 20a thereof and extending from a location near the crankshaft 14 to the vicinity of the piston pin 66. The lubricating oil that dropped from the second oil feed hole 80 to the oil groove 90 when the piston 18 is at the bottom dead center flows toward both the large and small end portions 62 and 64 due to the rocking motion of the connecting rod 20, as indicated by arrows. Thus, the large and small end portions 62 and 64 at which the connecting rod 20 is coupled to the crankshaft 14 and the piston 18, respectively, and their vicinities can be lubricated by the lubricating oil.

On the other hand, when the piston 18 is at the top dead center as illustrated in FIG. 5, the first and second oil feed holes 78 and 80 are located immediately above the connecting rod 20. The lubricating oil that dropped from the oil feed holes 78 and 80 to the oil groove 90 when the piston 18 is at the top dead center flows toward both the large and small end portions 62 and 64 due to the rocking motion of the connecting rod 20, as indicated by arrows. Thus, the large and small end portions 62 and 64 at which the connecting rod 20 is coupled to the crankshaft 14 and the piston 18, respectively, and their vicinities can be lubricated by the lubricating oil.

Further, the second oil feed hole 80 opens in a position such that the open end thereof is partly closed by an end wall 16b of the cylinder block 16 located opposite the end wall to which the cylinder head 34 is fixed. After passing through the second oil feed hole 80, the lubricating oil flows down along the end wall 16b and falls to the connecting rod 20 and the vicinities of a skirt 18a of the piston 18.

The compressor 1 of the first embodiment is provided with the first and second oil feed holes 78 and 80, and the first and second oil feed holes 78 and 80 allow the lubricating oil to reliably drop onto the piston 18, the piston pin 66 and the connecting rod 20, which are arranged below the frame 36. This is because the frame 36 is secured to the hermetic container 2 and the lubricating oil that flows from an upper region in the hermetic container 2 down to the upper surface 38a of the frame 36 is not acted upon by the centrifugal force produced by the rotation of the crankshaft 14. Accordingly, the lubricating oil can effectively lubricate the compression mechanism 6 without being influenced by the centrifugal force, whereby the lubrication performance and reliability of the compressor 1 can be improved.

When the piston 18 is at the bottom dead center, the first oil feed hole 78 is located immediately above the piston pin 66, and the second oil feed hole 80 is located immediately above the connecting rod 20. Accordingly, when the piston 18 is at the bottom dead center and thus the refrigerant pressure in the cylinder bore 26 is low, the lubricating oil can be made to drop from the first and second oil feed holes 78 and 80 directly onto the piston pin 66 and the connecting rod 20, respectively, without being influenced by the pressure of the refrigerant gas slightly leaking from the cylinder bore 26. The compression mechanism 6 can therefore be lubricated more effectively, making it possible to further improve the lubrication performance of the compressor 1.

When the piston 18 is at the top dead center, the first and second oil feed holes 78 and 80 are located right above the connecting rod 20. Thus, also when the piston 18 is at the top dead center and thus the refrigerant pressure in the cylinder bore 26 is high, the lubricating oil can be made to drop from the first and second oil feed holes 78 and 80 directly at least onto the connecting rod 20. The compression mechanism 6 can therefore be lubricated more effectively, making it possible to further improve the lubrication performance of the compressor 1.

Further, the frame 36 has the oil reservoir sections 82 and 84 for temporarily storing the lubricating oil that flows from the upper region in the hermetic container 2 down to the upper surface 38a of the frame 36. It is therefore possible to cause the lubricating oil to intermittently drip little by little, and since the compression mechanism 6 can be lubricated more effectively, the lubrication performance of the compressor 1 can be further improved.

Also, the connecting rod 20 has the oil groove 90 formed in the upper surface 20a thereof, and the oil groove 90 permits the lubricating oil dropped from the first and second oil feed holes 78 and 80 onto the connecting rod 20 to be guided to the large and small end portions 62 and 64 at which the connecting rod 20 is coupled to the crankshaft 14 and the piston pin 66. Thus, since the compression mechanism 6 can be lubricated more effectively, the lubrication performance of the compressor 1 can be further improved.

The present invention is not limited to the foregoing embodiment and may be modified in various ways.

Specifically, in the above embodiment, a carbon dioxide refrigerant is exemplified as the working fluid for the compressor 1, but the working fluid to be used is not limited to the carbon dioxide refrigerant. Where a carbon dioxide refrigerant is used as the working fluid, the working fluid discharged from the compression mechanism 6 is in a supercritical state and thus the pressure thereof is very high, so that high pressure may possibly prevail in the interior of the hermetic container 2. Consequently, the lubricating oil dropping, in particular, from the first oil feed hole 78 directly onto the piston pin 66 is greatly influenced by the pressure of the working fluid. With the aforementioned configuration, however, the compression mechanism 6 can be effectively lubricated without the influence of the pressure of the working fluid, whereby the lubrication performance of the compressor 1 can advantageously be enhanced.

Also, in the foregoing embodiment, the displacement type compressor 1 is explained by way of example. The present invention is applicable to hermetic type fluid machines in general, such as scroll compressor and expander, and fluid machines to which the invention is applied can of course be used as devices constituting refrigeration cycles incorporated in apparatuses other than automatic vending machines.

1 compressor (fluid machine) 2 hermetic container 2a inside bottom 4 electric motor (driving unit) 6 compression mechanism (driven unit) 14 crankshaft (rotary shaft) 16 cylinder block 16a upper surface 18 piston 20 connecting rod 20a upper surface 26 cylinder bore 36 frame 38a upper surface 66 piston pin 70 oil passage (lubrication mechanism) 72 oil pipe (lubrication mechanism) 78 first oil feed hole 80 second oil feed hole 82 oil reservoir section 84 oil reservoir section 90 oil groove