A CO.sub.2 compressor is disclosed for forcing and moving a lubricant under discharge pressure. If the oil path is reduced in size or a pressure reducing part is inserted to handle the large differential pressure caused between the discharge pressure and the intake pressure, the oil path would become liable to be easily clogged by foreign matter. In view of this, an intermittent oil supply mechanism is formed in the oil path using the sliding contact portion between a fixed member of the compressor body and a movable member. Thus, the substantial lubrication time period is shortened and the amount of oil supplied is limited.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a CO.sub.2 compressor for compressing the 
CO.sub.2 (carbon dioxide) refrigerant used in an air-conditioning system 
or, more particularly, to a lubricant supply unit for the CO.sub.2 
compressor. 
2. Description of the Related Art 
In an air-conditioning system using a fluoride such as HFC134 as a 
refrigerant, as has been widely used in the prior art, a lubricant supply 
unit is employed in which a lubricant such as a refrigerating machine oil 
mixed in advance with the refrigerant is separated from the refrigerant 
compressed and temporarily held in the discharge chamber of the 
refrigerant compressor, and the lubricant thus separated is forced by the 
differential pressure between the discharge pressure and the intake 
pressure of the compressor itself, or the differential pressure between 
the discharge pressure or the intake pressure and the pressure 
intermediate of the two pressures, without using a lubricant pump or the 
like requiring driving power, thereby supplying the lubricant to the 
sliding parts or the like of the refrigerant compressor requiring 
lubrication for forcibly lubricating such parts. 
In the lubricant supply unit described above, if the differential pressure 
between the discharge pressure and the intake pressure used for forcing 
the lubricant increases with the rotational speed of the compressor, the 
flow rate of the lubricant sometimes increases more than necessary. 
Therefore, as described in Japanese Unexamined UM Publication (Kokai) No. 
59-119992, for example, a pressure reducing part such as a thin restrictor 
or a porous material is inserted in an oil path, or the oil path of the 
lubricant is narrowed and lengthened, to increase the resistance thereof, 
thereby to suppress the flow rate of the lubricant. 
In an air-conditioning system using CO.sub.2 as a refrigerant, the 
differential pressure between intake pressure and discharge pressure is 
about five times higher than that for an air-conditioning system using an 
ordinary refrigerant such as HFC134. For forcible lubrication by forcing 
the lubricant under the differential pressure between the discharge 
pressure and the intake pressure of the refrigerant compressor using 
CO.sub.2 as a refrigerant, it is necessary to reduce the flow rate of the 
lubricant much more than when an ordinary refrigerant is used. Thus, a 
restrictor, or a like pressure reducing part, arranged in the oil path is 
required to be very thin and long. 
Fabrication of a thin, long pressure reducing part for use in the lubricant 
path requires labor for machining, which leads to a high cost. Not only 
that, foreign matter such as metal dust generated at the time of machining 
and sometimes remaining attached to the parts constituting a refrigeration 
cycle, or foreign matter or a highly viscous lump produced when a 
condensing material mixed, though rarely, in the refrigerant or the 
lubricant is condensed, can clog the pressure reducing parts such as a 
thin restrictor formed in the lubricant supply unit and prevents stable 
lubrication. This can reduce the performance and reliability of the 
compressor and hence of the air-conditioning system. 
SUMMARY OF THE INVENTION 
The object of the present invention is to cope with the above-mentioned 
problems of the conventional lubricant supply unit used for the CO.sub.2 
compressor and to obviate the problems with novel means whereby the oil 
path of the lubricant supply unit of the CO.sub.2 compressor is prevented 
from being clogged with foreign matter thereby to assure the stable supply 
of a proper amount of lubricant while at the same time reducing the 
fabrication cost of the parts associated with the lubricant supply unit of 
the CO.sub.2 compressor. 
According to the present invention, as a means for solving the problems 
described above, there is provided a CO.sub.2 compressor described in each 
of the appended claims. 
In a CO.sub.2 compressor according to this invention, the lubricant stored 
in an oil tank is forced by the differential pressure between the 
outlet-side pressure and the inlet-side pressure and supplied under 
pressure to the parts requiring lubrication. Therefore, the lubricant 
supply unit which consumes power such as a lubricant pump is not required. 
Also, in spite of the very large differential pressure between the 
discharge pressure and the intake pressure which is a problem unique to a 
refrigerant compressor of an air-conditioning system using the CO.sub.2 
refrigerant, the lubricant is supplied to the parts requiring lubrication 
by adjusting the lubricant flow rate without using any pressure reducing 
parts for reducing the size of the lubricant flow path. Therefore, as 
compared with the case of using a pressure reducing part such as a very 
thin restrictor to meet the large differential pressure, the likelihood of 
the pressure reducing parts being clogged with foreign matter is 
eliminated, and a stable, reliable lubricant supply unit can be realized. 
Further, the absence of the process for machining the pressure reducing 
parts decreases the manufacturing cost. 
More specifically, the CO.sub.2 compressor according to the present 
invention comprises what is called an intermittent lubrication mechanism 
arranged at least in a part of the oil path for supplying oil 
intermittently. Therefore, the amount (flow rate) of the lubricant supply 
can be freely set and changed by adjusting the lubrication time length 
with the intermittent lubrication mechanism without any pressure reducing 
parts in the oil path. As a result, there is no problem of the oil path 
being clogged up with foreign matter which otherwise might be caused in 
the pressure-reducing parts used in the oil path. Thus, a stable and 
reliable lubricant supply unit can be realized. At the same time, the 
eliminated need of machining the pressure-reducing parts can reduce the 
manufacturing cost. 
In the case where the CO.sub.2 compressor according to the present 
invention is constituted of a scroll-type CO.sub.2 compressor, the 
intermittent lubrication mechanism arranged in the oil path can be 
configured of an end plate of the movable scroll of the scroll-type 
compressor and a fixed member opposed thereto. Since the oil path is 
automatically opened and closed by the orbiting of the end plate, it is 
not necessary to provide the intermittent lubrication mechanism with a 
special valve and driving means thereof or the like. In this case, the 
intermittent lubrication mechanism can be constructed between the back 
side of the end plate of the movable scroll and the surface of the fixed 
member opposed thereto or between the front side of the end plate of the 
movable scroll and the surface of the fixed member opposed thereto. 
In the case where the CO.sub.2 compressor according to this invention is 
constituted of a piston-type compressor especially having a reciprocating 
piston, on the other hand, the intermittent lubrication mechanism arranged 
in the oil path can be constructed between the piston and the cylinder 
bore into which the piston is inserted slidably. In this case, the opening 
of the oil path to the cylinder bore is opened or closed by the 
reciprocating motion of the piston. The oil path is automatically opened 
or closed by the piston and therefore provision of a special valve means 
is not required for the intermittent lubrication mechanism. Also, in the 
case where a piston ring is provided for the piston, the intermittent 
lubrication mechanism can be constructed between the piston ring and the 
cylinder bore into which the piston is slidably inserted. In this case, 
the whole structure can be simplified by constructing a part of the oil 
path with a piston ring groove.

DESCRIPTION OF THE REFERRED EMBODIMENTS 
FIG. 1 illustrates an electric motor driven CO.sub.2 compressor of scroll 
type constituting a CO.sub.2 compressor according to a first embodiment of 
the invention. A major right portion of the internal space of a main 
housing 1 is occupied by a motor 2 making up a drive unit. Specifically, a 
field core 3 is fixed along the inner surface of the housing 1, and an 
armature 4 having a plurality of permanent magnets therein is integrally 
supported by a shaft 5, thus constituting an AC motor 2. The armature 4 is 
axially supported by front and rear bearings 6a, 6b for supporting the 
shaft 5 and is adapted to rotate freely with respect to the field core 3. 
An end of the shaft 5 extends into a compressor housing 7 integrated, by 
being screwed, to the housing 1 and thereby forms a crank 5a eccentric 
with respect to the axial center of the shaft 5. The crank 5a rotatably 
supports a boss 9c at the center of a movable scroll 9 through a bearing 
8. Though not shown, an end plate 9d of the movable scroll 9 is provided 
with an anti-rotation mechanism for preventing rotation, while allowing 
orbiting, of the movable scroll 9. 
A sliding unit 22 is formed in sliding contact with the back surface 9g of 
the end plate 9d of the movable scroll and the left end surface 7e in FIG. 
1 of the compressor housing 7 as thrust receiving surfaces. In this way, a 
thrust supporting mechanism is configured in which the fluid is compressed 
in the working chamber formed between volute blades 9f, 11f of two scrolls 
9, 11, and the resulting compressive reaction force generated thereby 
pushes the movable scroll 9 rightward in the drawing while at the same 
time axially supporting the movable scroll 9. Thus, while the compressive 
reaction force in the working chamber acts on the thrust receiving 
surfaces 9g, 7e of the sliding unit 22, a thrust is generated to push back 
the movable scroll 9 toward the fixed scroll 11. 
The central working chamber 12 formed between the volute blades 9f, 11f of 
the two scrolls 9, 11 combined in mesh with each other is adapted to 
communicate with an outlet chamber 14 formed as a space outside the end 
plate 11d of the fixed scroll 11 when the discharge valve 13 constituting 
a check valve of constant-pressure open type opens. The outlet chamber 14, 
which is closed by a lid 15, communicates with the interior of the main 
housing 1 through a path not shown, and further, through the gaps of the 
field core 3 and the coil 19 of the motor 2, communicates with an outlet 
port 23. The outlet port 23 is connected to the refrigeration cycle of the 
air-conditioning system using CO.sub.2 as a refrigerant. 
According to the first embodiment, an intake port 16 is arranged at the 
upper part of the end plate 11d of the fixed scroll 11. When the outermost 
one of a plurality of crescent working chambers 17 formed between the 
volute blades 9f, 11f nearer to the outer periphery from the center of the 
two scrolls 9, 11 opens toward the outer periphery, the particular working 
chamber 17 communicates with the intake port 16 so that the CO.sub.2 to be 
compressed is allowed into the intake port 16. 
The electric motor driven CO.sub.2 compressor of a scroll type according to 
this embodiment has the configuration described above. When the coil 19 of 
the motor 2 is supplied with AC power, therefore, the armature 4 and the 
shaft 5 integrated with the armature 4 are rotationally driven, and like 
the ordinary scroll-type compressor, the movable scroll 9 is rotationally 
driven by the crank 5a with an eccentric shaft. In view of the fact that 
the movable scroll 9 is allowed to orbit but not to rotate by the 
anti-rotation mechanism, not shown, however, the crescent working chambers 
17 formed between the volute blades 9f, 11f of the two scrolls 9, 11 allow 
the CO.sub.2 gas therein from the intake port 16 when the outer peripheral 
portion of the working chambers 17 is open. After the same outer 
peripheral portion closes, the CO.sub.2 gas gradually moves radially 
inward while being reduced in volume. Thus, the CO.sub.2 gas is compressed 
into a high pressure. The compressed CO.sub.2 gas is discharged into the 
central working chamber 12 when the crescent working chambers 17 open 
toward the central working chamber 12. Further, when the pressure of the 
working chamber 12 exceeds the opening pressure of the outlet valve 13, 
the outlet valve 13 opens so that the compressed CO.sub.2 is sent into the 
outlet chamber 14. 
The compressed CO.sub.2 gas in the outlet chamber 14 flows into the main 
housing 1 and toward the outlet port 23 through a path not shown as 
indicated by arrow. In the meantime, the lubricant like the refrigerating 
machine oil mixed with CO.sub.2 as a refrigerant is separated and stays in 
the oil tank 21 on the bottom of the housing 1. In the process, the 
lubricant, of course, lubricates the internal sliding parts such as the 
bearings of the motor 2. The pressure of the compressed CO.sub.2, i.e. the 
discharge pressure is exerted on the lubricant held in the main housing 1 
and hence held in the oil tank 21 formed on the bottom thereof. The 
compressed CO.sub.2 gas flowing through the gaps of the internal component 
parts of the motor 2 in the housing 1 also acts to cool the parts 
including the coil 19 of the motor 2, etc. 
The feature of the first embodiment lies in an oil path 20 establishes a 
communication between the compressor housing 7. The oil path 20 
communicates between the oil tank 21 formed in the lower part of the main 
housing 1 for storing the lubricant separated from the CO.sub.2 
refrigerant and the outlet port 20a opening at the position operated by 
the orbiting motion of the end plate 9d of the movable scroll, on the end 
surface 7e of the housing 1 forming the sliding unit 22 in sliding contact 
with the back surface 9g of the end plate 9d of the movable scroll 9. 
FIG. 2 is a side view taken in line II--II in FIG. 1, and the four diagrams 
(a), (b), (c) and (d) thereof show the state of the movable scroll 9 moved 
in increments of 90.degree. from the state (a). In (a) of FIG. 1, the 
outlet port 20a of the oil path is not covered with the end plate 9d of 
the movable scroll 9 but opens toward the intake chamber 24. Therefore, 
the internal pressure of the oil tank 21, i.e. the differential pressure 
between the discharge pressure of the CO.sub.2 compressor and the intake 
pressure of the intake chamber 24 causes the lubricant in the oil tank 21 
to be moved under pressure to the discharge port 20a formed in the sliding 
unit 22 through the oil path 20. As a result, the lubricant is supplied to 
and sufficiently lubricates the sliding contacting portions of the volute 
blades 9f, 11f of the two scrolls 9, 11 forming the working chambers 17 
and the working chamber 12. 
In the state shown in (b) to (d) of FIG. 2 where the movable scroll 9 is 
orbited and the discharge port 20a is covered by the back surface 9g of 
the end plate 9d, the flow of the lubricant passing through the oil path 
20 is shut off. In the process, the back surface 9g of the end plate 9d is 
pressed against the end surface 7e of the compressor housing 7 by the 
compressive reaction force exerted in the working chambers 12, 17. The 
discharge port 20a thus is closed up positively. As a consequence, the 
lubricant is supplied intermittently from the outlet port 20a and the time 
length of supplying the lubricant is shortened substantially. This in turn 
makes it possible to increase the amount of lubricant supplied through the 
outlet port 20a during a given time when the outlet port 20a is open. 
Therefore, the pressure-reducing parts such as the restrictor for limiting 
the flow rate of the lubricant is not required in the oil path 20. As a 
result, the problems of foreign matter clogging the pressure reducing 
parts and the additional cost of machining are obviated. Thus, the 
lubricant can be supplied stably and positively, while at the same time 
reducing the cost and improving the performance and reliability of the 
compressor. 
In the above-mentioned case, the substantial time length of supplying the 
lubricant and the amount of lubricant supplied can be changed by changing 
the opening position of the outlet port 20a of the oil path 20 on the end 
surface 7e of the compressor housing 7. The amount of lubricant supplied 
can thus be easily changed according to the type of the compressor. The 
same function is obtained by opening a communication hole of a retainer or 
the like in registry with the outlet port 20a, which retainer or the like 
is inserted as a sliding member into the end surface 7e of the housing 7 
forming the sliding unit 22. 
In the first embodiment shown, the intermittent oil supply mechanism having 
the outlet port 20a is configured on the sliding unit 22 between the back 
surface 9g of the end plate 9d of the movable scroll 9 and the end surface 
7e of the compressor housing 7. As an alternative, the intermittent oil 
supply mechanism can be formed between the other surface, i.e. the front 
surface 9i of the end plate 9d of the movable scroll 9 and a protruded 
portion, not shown, formed to expand from the end plate 11d of the fixed 
scroll 11 in opposed relation to the front surface 9i. Also, the feature 
of the first embodiment is not limited to the electric motor driven 
scroll-type compressor enclosed in its entirety as shown but is applicable 
also to the scroll-type open CO.sub.2 compressor as well. 
FIG. 3 is a longitudinal front sectional view of a CO.sub.2 compressor of 
swash plate type configured as open type according to a second embodiment 
of the invention. In FIG. 3, numeral 31 designates a front housing, 
numeral 32 a swash plate mounted on a shaft 33, numeral 34 a cylinder 
block, numeral 34a a plurality of cylinder bores formed in the cylinder 
block 34 in parallel to the shaft 33, numeral 35 a piston slidably 
inserted into a cylinder bore 34a, numeral 36 a shoe arranged at the 
portion of the piston 35 where it is slidably coupled to the swash plate 
32, numerals 37a, 37b radial bearings for axially supporting the shaft 33, 
numerals 38a, 38b thrust bearings, and numeral 39 a valve plate. 
Numeral 40 designates a rear housing mounted at an end of the cylinder 
block 34 with the valve plate 39 therebetween. The rear housing 40 has an 
intake chamber 40a formed therein. An intake port 40b for receiving the 
CO.sub.2 gas to be compressed is arranged in the intake chamber 40a. 
Further, an oil separator 41 is mounted on the back of the rear housing 
40. These component parts are fastened to each other integrally by a 
through bolt or the like not shown. The oil separator 41 has a space 
formed therein for separating the lubricant from the CO.sub.2 refrigerant 
under pressure. The lower part of the oil separator 41 constitutes an oil 
tank 41a and the upper part thereof constitutes an outlet chamber 41b. An 
outlet port 41c communicating with the refrigeration cycle of the 
air-conditioning system, not shown, is formed in the upper part of the oil 
separator 41. Numeral 42 designates a gasket, numeral 43 an intake valve, 
and numeral 44 an outlet valve. 
The feature of the second embodiment lies in that an oil path 45a open to 
the wall surface of the cylinder bore 34a is formed through the oil tank 
41a of the oil separator 41, the rear housing 40, the gasket 42 and the 
cylinder block 34 in that order. The piston 35 is formed with an oil path 
45b in radial direction in such a position as to communicate with the oil 
path 45a when the piston 35 is at about the bottom dead center. Further, 
the shaft 33 is formed with an oil path 45c communicating with the parts 
requiring lubrication including radial bearings 37a, 37b, thrust bearings 
38a, 38b, and a shaft seal 46. When the oil paths 45a, 45b described above 
communicate with each other, the oil path 45c comes to communicate with 
these oil paths through an oil path 45d formed in the cylinder block 34 
thereby to receive the lubricant. 
Numeral 45e designates an oil path branching from the oil path 45b for 
supplying the lubricant to the sliding contact surfaces of the swash plate 
32 and the shoe 36. The oil path 45a formed in the upper part of the 
cylinder block 34 also communicates with the lower oil path 45a to receive 
the lubricant from the oil tank 41a through an oil path such as an oil 
groove not shown formed along the surface on which the gasket 42 of the 
valve plate 39 is mounted. 
As long as the swash plate chamber 47 containing the swash plate 32 remains 
to communicate with the intake chamber 40a in the rear housing 40 by a 
path not shown, the swash plate chamber 47 is kept under an intake 
pressure during the operation. In the absence of such a path, however, the 
swash plate chamber 47 naturally assumes a pressure intermediate between 
the discharge pressure of the outlet chamber 41b and the intake pressure 
of the intake chamber 40a. Therefore, the pressure of the swash plate 
chamber 47 is lower than the discharge pressure. Consequently, in the 
example shown in FIG. 3, the lubricant stored in the oil tank 41a is 
supplied under pressure to the parts requiring lubrication, due to the 
differential pressure described above, only when any one of the pistons 35 
reaches the neighborhood of the bottom dead center and the oil paths 45a, 
45d of the cylinder block 34 communicate with the oil path 45b of the 
piston 35. As a result, the lubricant is supplied intermittently, and the 
amount of the lubricant supplied is properly adjusted without any pressure 
reducing parts such as a restrictor in the oil paths, thereby attaining 
substantially the same effect as the first embodiment. 
Though not shown, in a CO.sub.2 compressor with a piston ring mounted on 
the piston thereof as a modification of the second embodiment, an 
intermittent oil supply mechanism can be configured of an opening of the 
oil path formed in the cylinder bore, the cylindrical surface of the 
piston and the sliding surface of the piston ring by using the piston ring 
groove as a part of the oil path. Also, as in the first and second 
embodiments, an electric motor driven enclosed compressor of a piston type 
can be configured.