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Patent Searching and Data


Title:
COMPRESSOR
Document Type and Number:
WIPO Patent Application WO/2005/050023
Kind Code:
A1
Abstract:
A cover member (32) is provided on the side of an upper surface (7e) of the main bearing member (7). A space (31) between a main bearing member (7) and the cover member (32) is a passage through which has lubricated a main bearing (7a) is returned to an oil reservoir (16). Refrigeration oil which returns to the oil reservoir (16) is isolated from a main flowing place of working fluid. With this, refrigeration oil and working fluid are prevented from being mixed with each other, and an amount of refrigeration oil discharged out from a compressor together with working fluid is reduced.

Inventors:
Hasegawa, Hiroshi
Okaichi, Atsuo
Nishiwaki, Fumitoshi
Application Number:
PCT/JP2004/017436
Publication Date:
June 02, 2005
Filing Date:
November 17, 2004
Export Citation:
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Assignee:
MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD. (1006, Oaza Kadoma Kadoma-shi, Osaka, 571-8501, JP)
Hasegawa, Hiroshi
Okaichi, Atsuo
Nishiwaki, Fumitoshi
International Classes:
F04C29/02; F04C18/356; F04C23/00; (IPC1-7): F04C29/02
Foreign References:
US4878820A1989-11-07
US4955797A1990-09-11
EP1233186A22002-08-21
Other References:
PATENT ABSTRACTS OF JAPAN vol. 006, no. 069 (M - 125) 30 April 1982 (1982-04-30)
PATENT ABSTRACTS OF JAPAN vol. 014, no. 540 (M - 1053) 29 November 1990 (1990-11-29)
Attorney, Agent or Firm:
Shimizu, Yoshihiro (3rd Floor, Yashiro Building 14-4 Takadanobaba, 2-chom, Shinjyuku-ku Tokyo, 169-0075, JP)
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Claims:
CLAIMS
1. A compressor comprising a rotational motor having a stator and a rotor, a compression mechanism which has a lower space below said rotational motor and which is rotated by said rotor for compressing working fluid, and a container which accommodates said rotational motor and said compression mechanism and which is provided at its bottom with an oil reservoir for lubricant oil, in which said compression mechanism comprises a shaft to which said rotor is fixed, a main bearing which supports said shaft, oil supply means for supplying the lubricant oil from said oil reservoir to said main bearing, and an oilreturning passage through which the lubricant oil which lubricates the main bearing is returned to said oil reservoir, wherein said oilreturning passage is isolated from a main flowing place of the working fluid which was discharged from said compression mechanism into said lower space.
2. The compressor according to claim 1, wherein said oilreturning passage is a passage through which the lubricant oil discharged from an upper end of the main bearing is returned to said oil reservoir.
3. A compressor comprising a rotational motor having a stator and a rotor, a compression mechanism which has a lower space below said rotational motor and which is rotated by said rotor for compressing working fluid, and a container which accommodates said rotational motor and said compression mechanism and which is provided at its bottom with an oil reservoir for lubricant oil, in which said compression mechanism comprises a shaft to which said rotor is fixed, a cylinder, a main bearing which supports said shaft on the upper side of said cylinder, a main bearing member forming said main bearing, oil supply means which supplies the lubricant oil from said oil reservoir to said main bearing, and an oilreturning passage through which the lubricant oil which lubricated said main bearing is returned to said oil reservoir, wherein a cover member for covering at least a portion of said main bearing member is provided on an upper surface side of said main bearing member, said oilreturning passage is a space between said main bearing member and said cover member.
4. The compressor according to claim 3, wherein said cover member is shaped along an upper surface of said main bearing member.
5. The compressor according to claim 3, wherein said cover member is of circular shape whose center corresponds to said shaft.
6. The compressor according to claim 5, wherein said cover member has such an outer diameter that the entire oilreturning passage can be covered with said cover member.
7. The compressor according to any one of claims 1 to 6, wherein carbon dioxide is used as the working fluid.
Description:
DESCRIPTION COMPRESSOR Technical Field The present invention relates to a compressor used for a refrigerator-freezer, an air conditioner and the like.

Background of the Invention A hermetical type rotary compressor is widely used for a refrigerator-freezer, an air conditioner and the like because it is small in size and its structure is simple. A structure of the hermetical type rotary compressor such as the rotary compressor is described in a non-patent document 1, ["Air-Conditioning and Refrigeration handbook", new edition 5, volume 11, machine", Air-Conditioning and Refrigeration Institute, 1993, paragraphs 30 to 43]. The structure of the conventional hermetical type rotary compressor will be explained using Figs. 4 and 5 based on the rotary compressor.

Fig. 4 is a vertical sectional view of the conventional rotary compressor. The rotary compressor shown in Fig. 4 comprises a container 1, a shaft 2 having an eccentric portion 2a, a cylinder 3, a roller 4, a vane 5, a spring 6, a main bearing member 7 having a main bearing 7a supporting the shaft 2 and a discharge hole 7c, an auxiliary bearing member 8 having an auxiliary bearing 8a which supports the shaft 2, a stator 11 which is shrink fitted into the container 1, and a rotor 12 which is shrink fitted over the shaft 2. Sliding surfaces of the main bearing 7a and the auxiliary bearing 8a are provided with helical grooves 7b and 8b, respectively. In the above structure, a portion thereof comprising a stator 11 and a rotor 12 is called a rotational motor, and a portion thereof in which a suction chamber and a compression chamber (not shown) are formed in the cylinder 3 and working fluid is compressed as the rotor 12 rotates is called a compression mechanism.

The stator 11 is provided at its outer periphery with a plurality of notches 11 which serve as passages of working fluid. A gap 18 is provided between the stator 11 and the rotor 12. The container 1 is provided with an introduction terminal 13 for energizing the stator 11, a suction pipe (not shown) for introducing working fluid from the refrigeration cycle into the cylinder 3, a discharge pipe 15 for discharging the working fluid from the container 1 into the refrigeration cycle, and an oil reservoir 16 in which refrigeration oil is reserved.

The operation of the rotary compressor having the above-described structure will be explained.

If the stator 11 is energized through the introducing terminal 13 to rotate the rotor 12, the roller 4 is eccentrically rotated by the eccentric portion 2a, and volumes of the suction chamber and the compression chamber are varied.

With this, the working fluid is sucked into the suction chamber and compressed in the compression chamber. The compressed working fluid is injected into a lower space 17 of the rotational motor through a discharge hole 7c. In a main flowing place of the injected working fluid, the working fluid collides against a lower end surface 12a of the rotor 12 and a strong turning flow is generated by the rotation of the rotor 12. Then, the working fluid passes through the notches lla and the gap 18, and is injected into an upper space 19 of the rotational motor and then, the working fluid is discharged outside of the container 1 from a discharge pipe 15.

On the other hand, as the shaft 2 rotates, the refrigeration oil in the oil reservoir 16 passes through the helical groove 8b to lubricate the auxiliary bearing 8a, and the refrigeration oil is pumped up to the eccentric portion 2a. A portion of the pumped up refrigeration oil lubricates and seals fit portions between the eccentric portion 2a and the roller 4, the upper and lower end surfaces of the roller 4, and a gap between the main bearing member 7 and the auxiliary bearing member 8, and the portion of the refrigeration oil flows into the suction chamber and the compression chamber, and the refrigeration oil is mixed with the working fluid, and they are discharged from the discharge hole 7c into the lower space 17.

The rest of refrigeration oil passes through the helical groove 7b as the shaft 2 rotates, and the refrigeration oil lubricates the main bearing 7a and is pumped up to an upper end 7d of the main bearing 7a. Thereafter, the refrigeration oil overflows from the upper end 7d and flows through the upper surface 7e of the main bearing member 7. A portion of the refrigeration oil is caught up by the turning flow of the working fluid generated in the lower space 17 and is mixed with the working fluid. The rest of refrigeration oil returns to the oil reservoir 16 through a plurality of communication holes 7f provided in an outer periphery of the main bearing member 7. A portion of the refrigeration oil mixed with the working fluid is separated in the lower space 17 or the upper space 19 of the rotational motor due to gravity or centrifugal force of the turning flow, and is returned to the oil reservoir 16.

The rest of refrigeration oil is discharged outside of the container 1 from the discharge pipe 15 together with the working fluid.

In the hermetical compressor such as the rotary compressor, a portion of the refrigeration oil reserved in the oil reservoir 16 is discharged from the container 1 in the course operation of the compressor. As a result, in a compressor having a large discharge amount of refrigeration oil, an oil level of the refrigeration oil in the oil reservoir 16 is lowered, the supply amount of refrigeration oil to the compression mechanism becomes insufficient, the lubrication of the compression mechanism becomes insufficient, abnormal wear is generated and reliability is deteriorated, the sealing of the compression mechanism against working fluid becomes insufficient, and the efficiency of the compressor is deteriorated.

Further, the refrigeration oil discharged from the compressor attaches to an inner wall of a heat exchanger to deteriorate the heat transfer coefficient between the working fluid and the inner wall. Thus, the performance of the refrigeration cycle is deteriorated. Therefore, the discharging amount of the refrigeration oil is reduced.

As a mechanism for reducing the discharge amount of the refrigeration oil, there is a method using an oil separating plate provided on an upper portion of the rotor 12 of the rotary compressor as shown in a patent document 1, [Japanese Patent Application Laid-open No. H8-28476 (paragraph 6, Figs. 1 to 3), for example. Fig. 5 is a detailed sectional view of a periphery of the oil separating plate. The rotor 12 has an upper end plate 12c and a lower end plate 12d for closing an insertion hole of a permanent magnet 12b. A plurality of through holes 12e formed in the rotor 12 so as to penetrate the rotor 12 in the vertical direction, and an oil separating plate 21 which is disposed above exits of the through holes 12e and which forms an oil separating space 20 between itself and an upper end plate 12c of the rotor 12 are fixed to the rotor 12 by a fixing member 22.

In the compressor having the above-described structure, a portion of the working fluid including oil drops of the refrigeration oil discharged into the lower space 17 of the motor from the compressor mechanism flows into the oil separating space 20 through the through holes 12e formed in the rotor 12. Here, the working fluid is discharged radially from an outer peripheral exit of the oil separating plate 21 by the centrifugal force, and blows against the coil end lib of the stator 11, and the working fluid and the refrigeration oil included in the working fluid are separated. Only the working fluid from which the refrigeration oil is separated flows upward, and is discharged out from the discharge pipe 15 provided on the upper portion of the container 1. On the other hand, refrigeration oil attached to the coil end llb of the stator 11 falls downward and returns into the oil reservoir 16 formed in the bottom of the container 1.

As described above, according to the conventional rotary compressor, when the refrigeration oil lubricates and seals a fit portion between the eccentric portion 2a and the roller 4 as well as the gap between the main bearing member 7 and the auxiliary bearing member 8, the refrigeration oil flows into the cylinder 3 and is mixed with the working fluid, or the refrigeration oil overflows from the upper end 7d of the main bearing 7a, the refrigeration oil is caught up by the turning flow in the lower space 17 and is mixed with the working fluid before the refrigeration oil returns to the oil reservoir 16, and the refrigeration oil is discharged outside of the container 1 from the discharge pipe 15 together with the working fluid.

As means for separating the refrigeration oil from the working fluid, a structure shown in Fig. 5 is used. In such a separating method, even if the refrigeration oil mixed in the working fluid blows against the coil end llb, the refrigeration oil does not attached to the coil end llb completely, and especially the amount of refrigeration oil mixed in the working fluid is large, the discharge amount of the refrigeration oil can not be reduced sufficiently. Of the working fluid flowing from the lower space 17 toward the upper space 19, this method is effectively only for working fluid passing through the through holes 12e formed in the rotor 12, and it is not possible to separate the refrigeration oil from working fluid which passes through the notches lla or gap 18.

The present invention has been accomplished to solve the problem, and it is an object of the invention to reduce the amount of refrigeration oil discharged from a compressor together with working fluid, to enhance the reliability and performance of the compressor, and to obtain a refrigeration cycle having high efficiency.

Summary of the Invention A first aspect of the present invention provides a compressor comprising a rotational motor having a stator and a rotor, a compression mechanism which has a lower space below said rotational motor and which is rotated by said rotor for compressing working fluid, and a container which accommodates said rotational motor and said compression mechanism and which is provided at its bottom with an oil reservoir for lubricant oil, in which said compression mechanism comprises a shaft to which said rotor is fixed, a main bearing which supports said shaft, oil supply means for supplying the lubricant oil from said oil reservoir to said main bearing, and an oil-returning passage through which the lubricant oil which lubricates the main bearing is returned to said oil reservoir, wherein said oil-returning passage is isolated from a main flowing place of the working fluid which was discharged from said compression mechanism into said lower space.

According to this aspect, since the lubricant oil which flows through the oil-returning passage and returns to the oil reservoir is isolated from the main flowing place of the working fluid. Therefore, the working fluid is prevented from being caught by turning flow generated in the lower space and from being mixed with the working fluid. Thus, the amount of refrigeration oil discharged out from the container can be reduced.

According to a second embodiment of the invention, in the compressor of the first embodiment, the oil-returning passage is a passage through which the lubricant oil discharged from an upper end of the main bearing is returned to the oil reservoir.

According to this aspect, the lubricant oil discharged from the upper end of the main bearing can be returned to the oil reservoir without being mixed with working fluid.

A third aspect of the invention provides compressor comprising a rotational motor having a stator and a rotor, a compression mechanism which has a lower space below the rotational motor and which is rotated by the rotor for compressing working fluid, and a container which accommodates the rotational motor and the compression mechanism and which is provided at its bottom with an oil reservoir for lubricant oil, in which the compression mechanism comprises a shaft to which the rotor is fixed, a cylinder, a main bearing which supports the shaft on the upper side of the cylinder, a main bearing member forming the main bearing, oil supply means which supplies the lubricant oil from the oil reservoir to the main bearing, and an oil-returning passage through which the lubricant oil which lubricated the main bearing is returned to the oil reservoir, wherein a cover member for covering at least a portion of the main bearing member is provided on an upper surface side of the main bearing member, the oil-returning passage is a space between the main bearing member and the cover member.

According to this aspect, since the oil-returning passage is isolated from the main flowing place of the working fluid by the cover member, the lubricant oil can be returned to the oil reservoir without being mixed with the working fluid.

According to a fourth aspect of the invention, in the compressor of the third aspect, the cover member is shaped along an upper surface of the main bearing member.

According to this aspect, the reduction of the space volume of the lower space can be minimized, and the reduction of the oil separating effect in the lower space can be minimized.

According to a fifth aspect of the invention, in the compressor of the third aspect, the cover member is of circular shape whose center corresponds to the shaft.

According to this aspect, it becomes easy to form the cover member, and it can be produced inexpensively.

According to a sixth aspect of the invention, in the compressor of the fifth aspect, the cover member has such an outer diameter that the entire oil-returning passage can be covered with the cover member.

According to this aspect, it is possible to completely prevent the refrigeration oil from being mixed with the working fluid.

According to a seventh embodiment of the invention, in the compressor of any one of the first to sixth aspects, carbon dioxide is used as the working fluid.

A density difference between the carbon dioxide and the refrigeration oil is small, and the refrigeration oil is prone to be caught by the flow of the carbon dioxide. According to this aspect, however, the oil-returning passage is isolated from the main flowing place of the carbon dioxide so that the refrigeration oil returning to the oil reservoir is prevented from being caught by the flow of the carbon dioxide. Therefore, environmentally friendly carbon dioxide can be used as the working fluid.

Brief Description of the Drawings Fig. 1 is a vertical sectional view of a rotary compressor according to a first embodiment of the present invention; Fig. 2 is a transverse sectional view of a compression mechanism of the rotary compressor shown in Fig. 1; Fig. 3 is a transverse sectional view of a rotational motor of the rotary compressor shown in Fig. 1; Fig. 4 is a vertical sectional view of a conventional rotary compressor; and Fig. 5 is a detailed sectional view of a periphery of an oil separating plate of a conventional compressor.

Detailed Description An embodiment of the present invention will be explained with reference to the drawings.

A rotary compressor of a first embodiment of the present invention has a similar structure as that of the conventional rotary compressor explained using Fig. 4, and the same elements are designated with the same symbols.

Fig. 1 is a vertical sectional view of the rotary compressor of the first embodiment. Fig. 2 is a transverse sectional view of a compression mechanism of the rotary compressor shown in Fig. 1, taken along the arrow Z1-Z1 in Fig.

1. Fig. 3 is a transverse sectional view of a lower space of a rotational motor of the rotary compressor shown in Fig. 1, taken along the arrow Z2-Z2 in Fig. 1.

The rotary compressor shown in the drawings includes a container 1, a compressor mechanism disposed in a lower portion of the container 1, and a rotational motor disposed in an upper portion of the compressor mechanism. The compression mechanism includes a shaft 2 which includes an eccentric portion 2a and which can rotate around a center axis L, a cylinder 3, a roller 4 which is fitted into the eccentric portion 2a and which eccentrically rotates in the cylinder 3 as the shaft 2 rotates, a vane 5 which reciprocates in a vane groove 3a of the cylinder 3 in a state in which a tip end of the vane 5 is in contact with the roller 4, a spring 6 which pushes the vane 5 against the roller 4, a main bearing member 7 which includes a main bearing 7a for supporting the shaft 2 and a discharge hole 7c for discharging working fluid from the cylinder 3 and which closes an upper opening of the cylinder 3, and an auxiliary bearing member 8 which has an auxiliary bearing 8a for supporting the shaft 2 and which closes a lower opening of the cylinder 3. Sliding surfaces of the main bearing 7a and the auxiliary bearing 8a are provided with helical grooves 7b and 8b, respectively, as oil supply means which supplies lubricant oil. A space between the cylinder 3 and the roller 4 sandwiched between the main bearing member 7 and the auxiliary bearing member 8 is divided into a suction chamber 9 and a compression chamber 10 by the vane 5.

The rotational motor includes a stator 11 fixed in the container 1 and a rotor 12 fitted into the shaft 2. The stator 11 is provided at its outer periphery with a plurality of notches lla which serve as passages for working fluid. A gap 18 is provided between the stator 11 and the rotor 12. The container 1 is provided at its upper portion with an introduction terminal 13 which energizes the stator 11 from outside of the container 1, and a discharge pipe 15 which discharges working fluid into the refrigeration cycle from the container 1. The container 1 is provided at its side with a suction pipe 14 which introduces the working fluid into a suction chamber 9 from the refrigeration cycle. The container 1 is provided at its bottom with an oil reservoir 16 in which refrigeration oil is reserved.

In the rotary compressor of this embodiment, in addition to the above structure, a cover member 32 is disposed on the side of the upper surface 7e of the main bearing member 7 (that is, on the side of the lower space 17 of the rotational motor), and separates a space 31 from the upper surface 7e. The size of the space 31 is about the same as a thickness of flow of refrigeration oil which overflows from the upper end 7d of the main bearing 7a and flows on the upper surface 7e of the main bearing member 7. The thickness of flow of the refrigeration oil is increased as the supply amount of the refrigeration oil to the main bearing 7a is greater and the viscosity of the refrigeration oil is higher.

The cover member 32 is of circular shape whose center corresponds to the shaft 2. The cover member 32 is shaped along the upper surface 7e of the main bearing member 7 and thus, the cover member 32 is provided with a projecting portion 32a which projects from the center of the main bearing member 7 to cover the main bearing 7a. The projecting portion 32a has a hole 32b through which the shaft 2 passes, and a flange 32c formed around the hole 32b. A gap 33 between the shaft 2 and the hole 32b is set as small as possible within such a range that no sliding is generated.

The cover member 32 is provided at its outer periphery with a circular edge 32d. The edge 32d has such a size that covers about half of the communication holes 7f of the main bearing member 7. The edge 32d is provided with a flange 32e.

The cover member 32 has a discharge hole 32f through which working fluid discharged from the discharge hole 7c of the main bearing member 7 flows upward. The location of the discharge hole 32f corresponds to that of the discharge hole 7c. A thick portion 32g is provided around the discharge hole 32f of the cover member 32 so that the discharge hole 32f and the discharge hole 7c are in communication with each other without a gap.

The thick portion 32g is in direct contact with the upper surface 7e of the main bearing member 7.

Next, the operation of the rotary compressor of this embodiment will be explained.

If the stator 11 is energized through the introduction terminal 13 to rotate the rotor 12, the roller 4 is eccentrically rotates by the eccentric portion 2a of the shaft 2, and the volumes of the suction chamber 9 and the compression chamber 10 are varied. With this, the working fluid is sucked into the suction chamber 9 from the suction pipe 14, and compressed in the compression chamber 10. The compressed working fluid is injected into the lower space 17 of the rotational motor through the discharge hole 7c of the main bearing member 7 and the discharge hole 32f of the cover member 32. In a main flowing place of the injected working fluid, the working fluid collides against the lower end surface 12a of the rotor 12, and strong turning flow is generated in the working fluid by the rotation of the rotor 12. Thereafter, the working fluid passes through the gap 18 between the stator 11 and the rotor 12 or through the notches lla of the stator 11, and is injected into the upper space 19 of the rotational motor and discharged outside of the container 1 from the discharge pipe 15.

On the other hand, the refrigeration oil in the oil reservoir 16 passes through the helical groove 8b of the auxiliary bearing 8a as the shaft 2 rotates, lubricates the auxiliary bearing 8a and is pumped up to the eccentric portion 2a of the shaft 2. A portion of the pumped up refrigeration oil lubricates and seals the fit portions between the eccentric portion 2a and the roller 4, and the gaps between the upper end surface of the roller 4 and the main bearing member 7, and between the lower end surface of the roller 4 and the auxiliary bearing member 8, and the portion of the refrigeration oil flows into the suction chamber 9 and the compression chamber 10, and the refrigeration oil is mixed with the working fluid, and they are discharged into the lower space 17 through the discharge hole 7c of the main bearing member 7 and the discharge hole 32f of the cover member 32.

A portion of the discharged refrigeration oil is separated from the working fluid in the lower space 17 and the upper space 19 of the rotational motor due to gravity or centrifugal force, but the rest of the discharged refrigeration oil is not separated from the working fluid and discharged outside of the container 1 from the discharge pipe 15 together with the working fluid.

As the shaft 2 rotates, the rest of the refrigeration oil passes through the helical groove 7b of the main bearing 7a, lubricates the main bearing 7a and is pumped up to the upper end 7d of the main bearing 7a. Thereafter, the refrigeration oil overflows from the upper end 7d, flows into the space 31 between the cover member 32 and the upper surface 7e of the main bearing member 7, and if the refrigeration oil reaches the edge 32d of the cover member 32, the flowing direction of the refrigeration oil is changed downward by the flange 32e, and the refrigeration oil is returned to the oil reservoir 16 through the plurality of communication holes 7f formed in the outer periphery of the main bearing member 7.

As described above, according to the rotational motor of the embodiment, an oil-returning passage through which the refrigeration oil which lubricates the main bearing 7a and overflows from the upper end 7d returns to the oil reservoir 16 is the space 31 between the cover member 32 and the upper surface 7e of the main bearing member 7. This oil-returning passage is completely isolated from the main flowing place of the working fluid which is discharged into the lower space 17 of the rotational motor from the discharge hole 32f. Therefore, the refrigeration oil which overflows from the upper end 7d of the main bearing 7a and returns to the oil reservoir 16 can completely be prevented from being mixed with the working fluid.

Therefore, according to the rotary compressor of the embodiment, the amount of refrigeration oil discharged out from the container 1 together with the working fluid can be reduced. That is, it is possible to avoid a case in which the oil level of the refrigeration oil is lowered, the lubrication of the compression mechanism becomes insufficient and the reliability is deteriorated, and a case in which the sealing performance of the compression mechanism becomes insufficient and the efficiency of the compression mechanism is deteriorated.

The influence which refrigeration oil discharged from the compressor attaches to the inner wall of the heat exchanger tube of the heat exchanger can be reduced. Therefore, the heat transfer coefficient between the working fluid and the inner wall of the heat exchanger tube is not deteriorated, and the performance of the refrigeration cycle can be enhanced.

In the rotary compressor of the embodiment, the projecting portion 32a of the cover member 32 is provided with the flange 32c, and the gap 33 between the shaft 2 and the cover member 32 is made small. With this structure, the refrigeration oil which overflows from the upper end 7d of the main bearing 7a can be prevented from leaking from the gap 33 upward of the cover member 32, that is, upward toward the lower space 17 of the rotational motor, and prevented from being caught by the flow of the working fluid. Therefore, the amount of refrigeration oil discharged outside of the container 1 together with the working fluid can further be reduced and thus, the effect obtained by the cover member 32 can further be enhanced.

Further, the cover member 32 (cross section thereof shown in Fig. 1) is shaped along the upper surface 7e of the main bearing member 7. Therefore, even if the space 31 having sufficient size for returning the refrigeration oil is provided between the cover member 32 and the upper surface 7e of the main bearing member 7, the reduction of the space volume of the lower space 17 can be minimized. Since the velocity of flow of the working fluid is reduced due to the large space volume of the lower space 17 of the rotational motor, the reduction of the separating effect of the refrigeration oil from the working fluid can be minimized. Since the retention time of the working fluid is long, the reduction of the separating effect, due to gravity, of the refrigeration oil from the working fluid can be minimized.

Since the cover member 32 is of circular shape (plan view thereof shown in of Fig. 3) whose center corresponds to the shaft, it is easy and inexpensive to shape the cover member 32, and the refrigeration oil which overflows from any of circumferential directions of the upper end 7d of the main bearing 7a can be returned to the oil reservoir 16 efficiently.

It is not always necessary that the cover member 32 is circular in shape, and the amount of discharged oil can be reduced only if the space 31 which comes into communication with the oil reservoir 16 from the main bearing 7a can be formed.

The flange 32e is provided on the edge 32d of the outer periphery of the cover member 32 and thus, the space 31 opens only toward the communication holes 7f of the main bearing member 7 which is in communication with the oil reservoir 16.

Therefore, the working fluid in the lower space 17 of the rotational motor does not easily flow into the space 31, and it is possible to prevent the working fluid and the refrigeration oil from being mixed with each other. With this, since the amount of refrigeration oil discharge outside of the container 1 together with the working fluid can be reduced, the effect of the cover member 32 can further be enhanced.

Since the cover member 32 covers a portion of the communication holes 7f of the main bearing member 7, the refrigeration oil which flowed through the space 31 can easily return to the oil reservoir 16 through the communication holes 7f, and the refrigeration oil which has been separated from the working fluid in the lower space 17 of the rotational motor due to gravity or the centrifugal force can return to the oil reservoir 16 from a portion of the communication holes 7f of the main bearing member 7 which is not covered with the cover member 32. Thus, the refrigeration oil is not prevented from separating from the working fluid in the lower space 17 of the rotational motor.

When carbon dioxide is used as the working fluid, as compared with a case in which flon is used as the working fluid, since the density of carbon dioxide is extremely great, the density difference between the refrigeration oil and carbon dioxide is reduced. Therefore, although the refrigeration oil which overflowed from the upper end 7d of the main bearing 7a is prone to be caught by the flow of carbon dioxide, since the oil-returning passage is isolated from the main flowing place of the working fluid in this embodiment, it is possible to prevent the refrigeration oil returning to the oil reservoir from being caught by the flow of carbon dioxide. For example, when the cover member 32 is provided, its effect is exhibited more remarkably, and environmentally friendly carbon dioxide can be used as working fluid.

According to the compressor of the present invention, the oil-returning passage is isolated from the main flowing place of the working fluid, lubricant oil returning to the oil reservoir, e. g. , the refrigeration oil which overflows from the upper end 7d of the main bearing 7a is prevented from being mixed with the working fluid. Therefore, the amount of refrigeration oil which is mixed with the working fluid and discharged from the compressor can be reduced, the reliability and efficiency of the compressor can be enhanced, and a refrigeration cycle having high efficiency can be obtained.

Industrial Applicability The compressor according to the present invention has a function for compressing and transporting working fluid, and is effective for a refrigerant type heat pump such as a refrigerator-freezer and an air conditioner. The compressor can also be used for a vacuum pump.