U.S. patent application number 12/297505 was filed with the patent office on 2009-04-23 for compressor.
This patent application is currently assigned to DAIKIN INDUSTRIES, LTD.. Invention is credited to Masahide Higuchi, Hideki Mori, Yasukazu Nabetani, Azusa Ujihara.
Application Number | 20090100861 12/297505 |
Document ID | / |
Family ID | 38624974 |
Filed Date | 2009-04-23 |
United States Patent
Application |
20090100861 |
Kind Code |
A1 |
Higuchi; Masahide ; et
al. |
April 23, 2009 |
COMPRESSOR
Abstract
A stator core of a motor has a plurality of oil return passages
extending through one surface and the other surface of the core. On
the other surface of the stator core, a hydraulic diameter of each
oil return passage is 5 mm or larger, and a ratio of a total area
of the oil return passages to an area of a virtual circle having a
diameter equal to a maximum outer diameter of the stator core is 5
to 15%. Lubricating oil accumulated on the other surface side of
the stator core is returned to an oil reservoir through the oil
return passages, and shortage of oil in the oil reservoir is
prevented. Furthermore, a cross sectional area of the stator core
can be securely kept, and motor efficiency is maintained.
Inventors: |
Higuchi; Masahide; (Shiga,
JP) ; Nabetani; Yasukazu; (Shiga, JP) ;
Ujihara; Azusa; (Shiga, JP) ; Mori; Hideki; (
Shiga, JP) |
Correspondence
Address: |
GLOBAL IP COUNSELORS, LLP
1233 20TH STREET, NW, SUITE 700
WASHINGTON
DC
20036-2680
US
|
Assignee: |
DAIKIN INDUSTRIES, LTD.
Osaka-shi, Osaka
JP
|
Family ID: |
38624974 |
Appl. No.: |
12/297505 |
Filed: |
April 16, 2007 |
PCT Filed: |
April 16, 2007 |
PCT NO: |
PCT/JP2007/058246 |
371 Date: |
October 17, 2008 |
Current U.S.
Class: |
62/468 ;
417/410.1 |
Current CPC
Class: |
F04B 39/0284 20130101;
F04C 23/008 20130101; F04C 29/028 20130101; F04C 18/3564 20130101;
F04C 29/045 20130101 |
Class at
Publication: |
62/468 ;
417/410.1 |
International
Class: |
F25B 43/00 20060101
F25B043/00; F04B 35/04 20060101 F04B035/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 19, 2006 |
JP |
2006-116226 |
Claims
1. A compressor comprising: a closed container having an oil
reservoir; a compression element disposed within the closed
container; and a motor disposed within the closed container, the
motor being arranged to drive the compression element via a shaft,
the motor including a stator core having a plurality of oil return
passages extending through a first surface of the stator core
located on a side closer to the oil reservoir than an opposite side
and through a second surface of the stator core located on the
opposite side, and a hydraulic diameter of each of the oil return
passages at the second surface of the opposite side of the stator
core being 5 mm or larger, and a ratio of a total area of the
plurality of oil return passages at the second surface of the
opposite side of the stator core to an area of a virtual circle
having a diameter equal to a maximum outer diameter of the stator
core being 5 to 15%.
2. The compressor as claimed in claim 1, wherein the stator core is
disposed radially outside of a rotor of the motor, and the oil
return passages are located on an outer circumferential side of the
stator core.
3. The compressor as claimed in claim 1, wherein a refrigerant in
the closed container is carbon dioxide.
Description
TECHNICAL FIELD
[0001] The present invention relates to a compressor to be used
for, for example, air conditioners, refrigerators and the like.
BACKGROUND ART
[0002] Conventionally, a compressor includes a closed container, a
compression element placed within the closed container, and a motor
placed in the closed container and acting to drive the compression
element via a shaft, with an oil reservoir formed at a bottom
portion of the closed container so that lubricating oil is
accumulated in the oil reservoir (see JP 2003-262192 A).
[0003] However, in the conventional compressor described above,
because passages extending through from upper to lower portions of
the motor are small, lubricating oil accumulated in the upper
portion of the motor less returns to the oil reservoir located
lower than the motor. This would cause occurrence of shortage of
oil in the oil reservoir, as a problem. As a result of this
shortage of oil, it would be impossible to effectively feed the
lubricating oil in the oil reservoir via the shaft to sliding parts
such as the compression element or the bearing of the motor,
resulting in deteriorated reliability of the compressor. In
particular, when carbon dioxide is used as the refrigerant,
involving use of a high-viscosity lubricating oil as the
lubricating oil, the lubricating oil would be even less return to
the oil reservoir.
SUMMARY OF THE INVENTION
[0004] Accordingly, an object of the present invention is to
provide a compressor which is prevented from shortage of oil in the
oil reservoir while motor efficiency of a motor is maintained.
[0005] In order to achieve the above object, the present invention
provides a compressor comprising:
[0006] a closed container having an oil reservoir;
[0007] a compression element placed within the closed container;
and
[0008] a motor which is placed within the closed container and
which drives the compression element via a shaft, wherein
[0009] a stator core of the motor has a plurality of oil return
passages extending through one surface of the stator core located
on its one side closer to the oil reservoir and the other surface
of the stator core located on its another side opposite to the oil
reservoir, and
[0010] on the other surface of the stator core,
[0011] a hydraulic diameter of each of the oil return passages is 5
mm or larger, and a ratio of a total area of the plurality of oil
return passages to an area of a virtual circle having a diameter
equal to a maximum outer diameter of the stator core is 5 to
15%.
[0012] In the compressor of the present invention, in the other
surface of the stator core, the hydraulic diameter of each of the
oil return passages is 5 mm or larger, and the ratio of the total
area of the plurality of oil return passages to the area of the
virtual circle having the diameter equal to the maximum outer
diameter of the stator core is 5 to 15%. Therefore, lubricating oil
accumulated on the other surface side of the stator core can be
returned to the oil reservoir located on the one surface side of
the stator core via the plurality of oil return passages, so that
oil shortage in the oil reservoir can be prevented. Moreover, the
cross-sectional area of the stator core can be ensured, and the
motor efficiency can be maintained. Particularly when carbon
dioxide is used as the refrigerant, in which use of a
high-viscosity lubricating oil is involved, the lubricating oil can
effectively be returned to the oil reservoir.
[0013] In one embodiment, the stator core is placed radially
outside of a rotor of the motor, and
[0014] the oil return passages are located on an outer
circumferential side of the stator core.
[0015] In the compressor of this embodiment, since the oil return
passages are located on the outer circumferential side of the
stator core, lubricating oil that has been scattered radially
outward by the rotor or lubricating oil that has stuck to the inner
circumferential surface of the closed container can effectively be
led to the oil return passages, so that oil shortage in the oil
reservoir can be prevented more reliably.
[0016] In one embodiment, a refrigerant in the closed container is
carbon dioxide.
[0017] In the compressor of this embodiment, since the refrigerant
within the closed container is carbon dioxide, in which use of a
high-viscosity lubricating oil is involved, the lubricating oil can
effectively be returned to the oil reservoir.
[0018] According to the compressor of the present invention, in the
other surface of the stator core, the hydraulic diameter of each of
the oil return passages is 5 mm or larger, and the ratio of the
total area of the plurality of oil return passages to the area of
the virtual circle having the diameter equal to the maximum outer
diameter of the stator core is 5 to 15% so that oil shortage in the
oil reservoir can be prevented and the motor efficiency can be
maintained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a longitudinal sectional view showing an
embodiment of a compressor of the invention;
[0020] FIG. 2 is a plan view of main part of the compressor;
[0021] FIG. 3 is a cross-sectional view of a vicinity of a motor in
the compressor;
[0022] FIG. 4 is an enlarged view of part A of FIG. 3;
[0023] FIG. 5 is a graph showing relationships of oil shortage and
motor efficiency with hydraulic diameter and area ratio;
[0024] FIG. 6A is a graph showing a relationship between area ratio
and motor-efficiency decreasing rate;
[0025] FIG. 6B is a graph showing a relationship between area ratio
and oil-level decreasing rate;
[0026] FIG. 7A is a graph showing a relationship between hydraulic
diameter and motor-efficiency decreasing rate;
[0027] FIG. 7B is a graph showing a relationship between hydraulic
diameter and oil-level decreasing rate.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Hereinbelow, the present invention will be described in
detail by way of embodiments thereof illustrated in the
accompanying drawings.
[0029] FIG. 1 shows a longitudinal sectional view which is an
embodiment of a compressor of the invention. This compressor
includes a closed container 1, a compression element 2 placed
within the closed container 1, and a motor 3 placed in the closed
container 1 and acting to drive the compression element 2 via a
shaft 12.
[0030] This compressor is a so-called vertical high-pressure
dome-type rotary compressor, in which the compression element 2 is
placed below and the motor 3 is placed above within the closed
container 1. The compression element 2 is driven by a rotor 6 of
the motor 3 via the shaft 12.
[0031] The compression element 2 sucks in a refrigerant gas from an
accumulator 10 through a suction pipe 11. The refrigerant gas can
be obtained by controlling unshown condenser, expansion mechanism
and evaporator that constitute an air conditioner as an example of
a refrigeration system in combination with the compressor.
[0032] The refrigerant gas, which is carbon dioxide, becomes as
high a pressure as about 12 MPa within the closed container 1.
Alternatively, R410A or R22 or other like refrigerant may be used
as the refrigerant.
[0033] In this compressor, a compressed high-temperature,
high-pressure refrigerant gas is discharged from the compression
element 2 to fill the closed container 1 therewith internally,
while the refrigerant gas is passed through a gap between the
stator 5 and the rotor 6 of the motor 3 to cool the motor 3. The
refrigerant gas is thereafter discharged outside from a discharge
pipe 13 provided on the upper side of the motor 3.
[0034] In lower portion of a high-pressure region within the closed
container 1 is formed an oil reservoir 9 in which lubricating oil
is accumulated. This lubricating oil moves from the oil reservoir 9
through oil passages (not shown) provided in the shaft 12 to
sliding parts such as the compression element 2 and a bearing of
the motor 3, thus lubricating the sliding parts.
[0035] When carbon dioxide is used as the refrigerant, the
lubricating oil to be used is a high-viscosity one. As this
lubricating oil, a lubricating oil having a viscosity of 5-300 cSt
at 40.degree. C. is used. This lubricating oil is exemplified by
polyalkylene glycol oil (such as polyethylene glycol and
polypropylene glycol), ether oil, ester oil, and mineral oil.
[0036] The compression element 2 includes a cylinder 21 fitted to
an inner surface of the closed container 1, and an upper-side end
plate member 50 and a lower-side end plate member 60 fitted to
upper and lower opening ends of the cylinder 21, respectively. A
cylinder chamber 22 is defined by the cylinder 21, the upper-side
end plate member 50 and the lower-side end plate member 60.
[0037] The upper-side end plate member 50 has a disc-shaped body
portion 51, and a boss portion 52 provided upwardly at a center of
the body portion 51. The shaft 12 is inserted into the body portion
51 and the boss portion 52. In the body portion 51 is provided a
discharge hole 51a communicating with the cylinder chamber 22.
[0038] A discharge valve 31 is fitted to the body portion 51 so as
to be positioned on one side of the body portion 51 opposite to the
side on which the cylinder 21 is provided. This discharge valve 31
is, for example, a reed valve which opens and closes the discharge
hole 51a.
[0039] A cup-type muffler cover 40 is fitted on the body portion 51
on its one side opposite to the cylinder 21 so as to cover the
discharge valve 31. The muffler cover 40 is fixed to the body
portion 51 by fixing members 35 (e.g., bolt). The boss portion 52
is inserted into the muffler cover 40.
[0040] The muffler cover 40 and the upper-side end plate member 50
define a muffler chamber 42. The muffler chamber 42 and the
cylinder chamber 22 are communicated with each other via the
discharge hole 51a.
[0041] The muffler cover 40 has a hole portion 43. By the hole
portion 43, the muffler chamber 42 and an outer side of the muffler
cover 40 are communicated with each other.
[0042] The lower-side end plate member 60 has a disc-shaped body
portion 61, and a boss portion 62 provided downwardly at a center
of the body portion 61. The shaft 12 is inserted into the body
portion 61 and the boss portion 62.
[0043] In short, one end portion of the shaft 12 is supported by
the upper-side end plate member 50 and the lower-side end plate
member 60. That is, the shaft 12 cantilevers. One end portion (on
the support end side) of the shaft 12 intrudes into the cylinder
chamber 22.
[0044] On the support end side of the shaft 12, an eccentric pin 26
is provided so as to be positioned within the cylinder chamber 22
of the compression element 2. The eccentric pin 26 is fitted into a
roller 27. The roller 27 is placed revolvable in the cylinder
chamber 22 so that compression action is exerted by revolving
motion of the roller 27.
[0045] In other words, one end portion of the shaft 12 is supported
by a housing 7 of the compression element 2 on both sides of the
eccentric pin 26. The housing 7 includes the upper-side end plate
member 50 and the lower-side end plate member 60.
[0046] Next, compression action of the cylinder chamber 22 is
explained.
[0047] As shown in FIG. 2, the cylinder chamber 22 is internally
partitioned by a blade 28 integrally provided with the roller 27.
That is, in a chamber on the right side of the blade 28, the
suction pipe 11 is opened in the inner surface of the cylinder
chamber 22 to form a suction chamber (low-pressure chamber) 22a. In
a chamber on the left side of the blade 28, the discharge hole 51a
(shown in FIG. 1) is opened in the inner surface of the cylinder
chamber 22 to form a discharge chamber (high-pressure chamber)
22b.
[0048] Semicolumnar-shaped bushes 25, 25 are set in close contact
with both surfaces of the blade 28 to provide a seal. Lubrication
with the lubricating oil is implemented between the blade 28 and
the bushes 25, 25.
[0049] Then, as the eccentric pin 26 eccentrically rotates along
with the shaft 12, the roller 27 fitted to the eccentric pin 26
revolves while the outer circumferential surface of the roller 27
keeps in contact with the inner circumferential surface of the
cylinder chamber 22.
[0050] As the roller 27 revolves in the cylinder chamber 22, the
blade 28 moves back and forth while both side faces of the blade 28
are held by the bushes 25, 25. Then, the low-pressure refrigerant
gas is sucked from the suction pipe 11 into the suction chamber 22a
and compressed into a high pressure in the discharge chamber 22b,
so that a high-pressure refrigerant gas is discharged from the
discharge hole 51a (shown in FIG. 1).
[0051] Thereafter, as shown in FIG. 1, the refrigerant gas
discharged from the discharge hole 51a is discharged via the
muffler chamber 42 outward of the muffler cover 40.
[0052] As shown in FIGS. 1 and 3, the motor 3 has the rotor 6, and
the stator 5 placed radially outside of the rotor 6 with an air gap
interposed therebetween.
[0053] The rotor 6 has a rotor body 610, and magnets 620 embedded
in the rotor body 610. The rotor body 610 is cylindrical shaped and
formed of, for example, multilayered electromagnetic steel plates.
The shaft 12 is fitted to a hole portion at a center of the rotor
body 610. Each of the magnets 620 is a flat permanent magnet. Six
of the magnets 620 are arrayed at center angles of equal intervals
in the circumferential direction of the rotor body 610.
[0054] The stator 5 has a stator core 510, and coils 520 wound
around the stator core 510. In FIG. 3, the coils 520 are partly
omitted in illustration.
[0055] The stator core 510 has an annular portion 511, and nine
teeth 512 protruding radially inwardly from an inner
circumferential surface of the annular portion 511 and arrayed
circumferentially at equal intervals. The stator core 510 is formed
of a plurality of multilayered steel plates. The coils 520 are
wound around the individual teeth 512, respectively, and not wound
over the plurality of teeth 512, hence a concentrated winding.
[0056] The motor 3 is a so-called 6-pole, 9-slot type one. By
electromagnetic force generated in the stator 5 caused by passing a
current through the coils 520, the rotor 6 is rotated along with
the shaft 12.
[0057] The stator core 510 has a plurality of oil return passages
530 extending through one surface (lower surface) 510a of the
stator core 510 located on its one side closer to the oil reservoir
9 and the other surface (upper surface) 510b of the stator core 510
located on the other side opposite to the oil reservoir 9.
[0058] The oil return passages 530 are located on the outer
circumferential side of the stator core 510. The oil return
passages 530 are formed by so-called core cuts of recessed grooves
or D-cut surfaces or the like formed in the outer circumferential
surface of the stator core 510. That is, the oil return passages
530 are spaces each surrounded by an inner surface of a core cut
and an inner circumferential surface 1b of the closed container
1.
[0059] The oil return passages 530 are provided radially outside of
the teeth 512, respectively, counting nine equal to that of the
teeth 512. The oil return passages 530 are formed each into a
generally rectangular shape as viewed along a center axis 1a of the
closed container 1.
[0060] In the other surface 510b of the stator core 510, the
hydraulic diameter of each oil return passage 530 is 5 mm or
larger, and the ratio of the total area of the plural oil return
passages 530 to the area of the virtual circle having a diameter
equal to the maximum outer diameter of the stator core 510
(hereinafter, referred to as area ratio) is 5 to 15%.
[0061] Given an area S of the oil return passage 530 on the other
surface 510b and a circumferential length L of the oil return
passage 530 on the other surface 510b as shown in FIG. 4, the
hydraulic diameter of the oil return passage 530 can be expressed
as 4S/L. FIG. 4 is an enlarged view of part A of FIG. 3.
[0062] The area S of the oil return passage 530 is, as shown by
hatching in FIG. 4, an area surrounded by the inner surface of the
recessed groove of the stator core 510 and the inner
circumferential surface 1b of the closed container 1. The
circumferential length L of the oil return passage 530 is, as shown
by bold line in FIG. 4, a value resulting from adding up a length
of the inner surface of the recessed groove of the stator core 510
and a length of the inner circumferential surface 1b of the closed
container 1.
[0063] The virtual circle having a diameter equal to the maximum
outer diameter of the stator core 510 is, as shown in FIG. 3,
coincident with the inner circumferential surface 1b of the closed
container 1. That is, the area of this virtual circle is coincident
with a cross-sectional area of the inside of the closed container 1
on the other surface 510b. The total area of the plurality of oil
return passages 530 refers to a total sum of areas S of the oil
return passages 530 on the other surface 510b.
[0064] According to the compressor constructed as described above,
the hydraulic diameter of each oil return passage 530 on the other
surface 510b of the stator core 510 is 5 mm or larger, and the area
ratio is 5 to 15%. Therefore, lubricating oil that has flowed to
the downstream side (upper side) of the motor 3 along with the
refrigerant gas so as to be accumulated on the other surface 510b
side of the stator core 510 can be returned to the oil reservoir 9
on the one surface 510a side of the stator core 510 via the
plurality of oil return passages 530, so that oil shortage in the
oil reservoir 9 can be prevented. Thus, by this prevention of oil
shortage, lubricating oil in the oil reservoir 9 can effectively be
fed via the shaft 12 to sliding parts such as the compression
element 2 and the bearing of the motor 3, so that the reliability
of the compressor is improved.
[0065] Moreover, the cross-sectional area of the stator core 510
can be ensured, and the motor efficiency can be maintained.
Particularly when carbon dioxide is used as the refrigerant, in
which use of a high-viscosity lubricating oil is involved, the
lubricating oil can effectively be returned to the oil reservoir
9.
[0066] In this case, if the hydraulic diameter of each oil return
passage 530 satisfies to be 5 mm only on the other surface 510b of
the stator core 510, the lubricating oil overcomes the viscosity by
its dead weight to move down along the oil return passages 530 up
to the oil reservoir 9.
[0067] In contrast to this, if the hydraulic diameter of each oil
return passage 530 is smaller than 5 mm, then the oil return
passages 530 are each formed into, for example, a slit shape as its
planar shape, so that the lubricating oil sticks to the other
surface 510b of the stator core 510 by its viscosity, thus not
going down along the oil return passages 530, and not moving to the
oil reservoir 9. That is, there is a problem of occurrence of oil
shortage. On the other hand, if the hydraulic diameter of each oil
return passage 530 is larger than 15 mm, then the effective surface
area of the annular portion 511 of the stator core 510 becomes
smaller, resulting in a deteriorated motor efficiency.
[0068] Further, if the area ratio is smaller than 5%, then the
number of oil return passages 530 becomes smaller, so that
lubricating oil cannot effectively be returned to the oil reservoir
9, giving rise to occurrence of oil shortage as a problem. On the
other hand, if the area ratio is larger than 15%, then the number
or area of the oil return passages 530 becomes larger, causing the
surface area of the stator core 510 to be smaller, so that the
motor efficiency decreases as a problem.
[0069] In this invention, preferably, the hydraulic diameter of
each oil return passage 530 is not more than 20 mm (more
preferably, not more than 15 mm), in which case the cross-sectional
area of the stator core 510 can more reliably be ensured and the
motor efficiency can more reliably be maintained.
[0070] Further, since the oil return passages 530 are located on
the outer circumferential side of the stator core 510, lubricating
oil that has been scattered radially outward by the rotor 6 or
lubricating oil that has stuck to the inner circumferential surface
1b of the closed container 1 can effectively be led to the oil
return passages 530, so that oil shortage in the oil reservoir 9
can more reliably be prevented.
[0071] Next, FIG. 5 shows relationships of oil shortage and motor
efficiency with hydraulic diameter and area ratio. In the figure,
the horizontal axis represents the hydraulic diameter of each oil
return passage, and the vertical axis represents the area ratio
(the ratio of the total area of the oil return passages to an
outer-diametral area of the stator core, i.e., the area of a circle
having a diameter equal to the outer diameter of the stator
core).
[0072] In a first region Z1, i.e., on condition that the hydraulic
diameter is 5 to 15 mm and the area ratio is 5 to 15%, then there
is no problem in oil shortage or motor efficiency.
[0073] In a second region Z2, i.e., on condition that the hydraulic
diameter is larger than 15 mm and that the area ratio is 5 to 15%,
there is a slight problem in motor efficiency, but no problem in
oil shortage.
[0074] In a third region Z3, i.e., on condition that the hydraulic
diameter is 5 mm or larger and the area ratio is larger than 15%,
there is no problem in oil shortage but is a problem in motor
efficiency.
[0075] In a fourth region Z4, i.e., on condition at least either
that the hydraulic diameter is smaller than 5 mm or that the area
ratio is smaller than 5%, there is no problem in motor efficiency
but is a problem in oil shortage.
[0076] Next, grounds of the graph of FIG. 5 are shown in FIGS. 6A,
6B, 7A and 7B.
[0077] FIG. 6A shows a relationship between area ratio (ratio of
the total area of the oil return passages to the outer-diametral
area of the stator core) and motor-efficiency decreasing rate. In
the figure, the vertical axis represents motor-efficiency
decreasing rate, where the motor efficiency decreases more and more
downward of the vertical axis. As can be seen from FIG. 6A, with
the area ratio over 15%, the motor efficiency is extremely
decreases.
[0078] FIG. 6B shows a relationship between area ratio (ratio of
the total area of the oil return passages to the outer-diametral
area of the stator core) and oil-level decreasing rate. In the
figure, the vertical axis represents oil-level decreasing rate,
where the oil level decreases more and more downward of the
vertical axis. As can be seen from FIG. 6B, with the area ratio
under 5%, the oil level extremely decreases.
[0079] In other words, since the motor efficiency decreases with
increasing total area of the oil return passages, the area ratio
(ratio of total area of oil return passages/outer-diametral area of
stator core) needs to be smaller than 15%. Also, since a smaller
total area of the oil return passages causes oil returnability to
worsen, enough oil level cannot be ensured. Therefore, the area
ratio (ratio of total area of oil return passages/outer-diametral
area of stator core) needs to be larger than 5%.
[0080] FIG. 7A shows a relationship between hydraulic diameter of
the oil return passages and motor-efficiency decreasing rate. In
the figure, the vertical axis represents motor-efficiency
decreasing rate, where the motor efficiency decreases more and more
downward of the vertical axis. As can be seen from FIG. 7A,
hydraulic diameters larger than 15 mm lead to occurrence of a
problem in motor efficiency.
[0081] FIG. 7B shows a relationship between hydraulic diameter of
the oil return passages and oil-level decreasing rate. In the
figure, the vertical axis represents oil-level decreasing rate,
where the oil level decreases more and more downward of the
vertical axis. As can be seen from FIG. 7B, with the hydraulic
diameter under 5 mm, the oil level extremely decreases.
[0082] In other words, a larger hydraulic diameter causes the
surface area of the annular portion 511 of the stator core 510 to
become smaller, so that the motor efficiency decreases. Therefore,
the hydraulic diameter needs to be smaller than 15 mm. Also, since
a smaller hydraulic diameter causes oil returnability to worsen,
enough oil level cannot be ensured. Therefore, the hydraulic
diameter needs to be larger than 5 mm.
[0083] It is noted that the present invention is not limited to the
above-described embodiment. For example, the compression element 2
may also be a rotary type one in which its roller and blade are
provided independent of each other. The compression element 2 may
further be a scroll type or reciprocating type one other than the
rotary type. The compression element 2 may also be a two-cylinder
type one having two cylinder chambers. The coils 520 may be of the
so-called distributed winding in which the coils 520 are wound over
the plurality of teeth 512.
[0084] Further, it is also allowable that the compression element 2
is provided above while the motor 3 is provided below. The oil
return passages 530 may be provided on the inner circumferential
side of the stator core 510, or provided at an intermediate portion
between the inner circumferential surface and the outer
circumferential surface of the stator core 510. Furthermore, the
oil return passages 530 may be provided at any position in the
circumferential direction of the stator core 510, and may be
provided at equal or unequal pitches.
* * * * *