U.S. patent application number 10/742609 was filed with the patent office on 2004-09-30 for electric compressor.
Invention is credited to Akashi, Hironari, Kakiuchi, Takashi, Katayama, Makoto, Kawabata, Hirotaka, Kojima, Takeshi, Kubota, Akihiko, Nagao, Takahide, Tsuboi, Kosuke.
Application Number | 20040191094 10/742609 |
Document ID | / |
Family ID | 32984308 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040191094 |
Kind Code |
A1 |
Kojima, Takeshi ; et
al. |
September 30, 2004 |
Electric compressor
Abstract
A compressor includes a motor unit formed of a stator and a
rotor, a compressor mechanism driven by the motor unit, and an
enclosed container accommodating the foregoing elements. The
compressor mechanism includes a cylinder block equipped with a
compressing chamber and a piston. A shaft directly coupled to the
rotor that drives the piston is supported by a double-sided bearing
system, namely, a main bearing and a sub bearing. This structure
allows preventing the shaft from slanting, and reducing a loss and
a noise caused by sliding. As a result, a low profile, highly
reliable and efficient compressor is obtainable.
Inventors: |
Kojima, Takeshi;
(Yokohama-shi, JP) ; Kakiuchi, Takashi;
(Yamato-shi, JP) ; Kawabata, Hirotaka;
(Fujisawa-shi, JP) ; Nagao, Takahide;
(Fujisawa-shi, JP) ; Tsuboi, Kosuke;
(Chigasaki-shi, JP) ; Akashi, Hironari;
(Chigasaki-shi, JP) ; Katayama, Makoto;
(Chigasaki-shi, JP) ; Kubota, Akihiko;
(Chigasaki-shi, JP) |
Correspondence
Address: |
ROSSI & ASSOCIATES
P.O. Box 826
Ashburn
VA
20146-0826
US
|
Family ID: |
32984308 |
Appl. No.: |
10/742609 |
Filed: |
December 19, 2003 |
Current U.S.
Class: |
417/415 |
Current CPC
Class: |
F04B 35/04 20130101 |
Class at
Publication: |
417/415 |
International
Class: |
F04B 017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2003 |
JP |
JP 2003-033377 |
Claims
What is claimed is:
1. An electric compressor comprising: (a) a motor unit including a
stator with a winding, and a rotor with a rotor iron-core and a
permanent magnet; (b) a compressor mechanism driven by the motor
unit and including: (b-1) a shaft including an eccentric shaft
section, a main shaft section and a sub shaft section, the main
shaft section and the sub shaft section sandwiching the eccentric
shaft section vertically and being placed coaxially,; (b-2) a
cylinder block including a compressing chamber; (b-3) a main
bearing, disposed in the cylinder block such that the main bearing
crosses with an axial core of the compressing chamber at right
angles, for rotatably supporting the main shaft section; (b-4) a
sub bearing, disposed in the cylinder block, for rotatably
supporting the sub shaft section; (b-5) a piston for reciprocating
in the compressing chamber; (b-6) a linking means for coupling the
piston with the eccentric shaft section; and (c) an enclosed
container for pooling lubricant oil and accommodating the motor
unit and the compressor mechanism.
2. The compressor of claim 1, wherein the main bearing does not
cross with a plane which includes an end section of rotor iron-core
on the compressor mechanism side and is orthogonal to an axial core
of the main shaft section.
3. The compressor of claim 2, wherein the main bearing is made of
iron-based material.
4. The compressor of claim 1, wherein the rotor iron-core has a
hollow bore at its end section on the compressor mechanism side,
and the main bearing extends into the bore.
5. The compressor of claim 4, wherein the main bearing is made of
non-magnetic material.
6. The compressor of claim 1, wherein the permanent magnet is made
of rare-earth material.
7. The compressor of claim 1, wherein the motor unit is driven at a
plurality of frequencies including a frequency not lower than a
commercial power frequency.
8. The compressor of claim 1, wherein the stator includes a
plurality of teeth, and the winding is wound on the teeth via
insulating material.
9. The compressor of claim 1, wherein the motor unit starts working
as an induction motor, and when its rotation becomes near a
synchronizing rotation, synchronous pull-in is carried out for
synchronous operation.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to electric compressors used
in refrigerators with freezers or air-conditioners.
BACKGROUND OF THE INVENTION
[0002] An electric compressor (hereinafter referred to simply as a
compressor) employed in freezers of home-use refrigerators has
undergone improvements for more efficient performance, such as use
of lubricant oil of lower viscosity, use of inverter driving, and
employment of synchronous motor. Those improvements have been done
for reducing power consumption of the compressor. At the same time,
the compressor is required to be more compact for increasing a
volume efficiency of the refrigerator.
[0003] A conventional compressor is disclosed, e.g. in Japanese
Patent Application Non-Examined Publication No. 2001-73948. This
compressor is improved its stator and main bearing. FIG. 5 shows a
vertical sectional-view of this compressor. In FIG. 5, enclosed
container 1 of the compressor pools lubricant oil 12 at its bottom
section. Container 1 accommodates motor unit 3 formed of stator 13
and rotor 14, and compressor mechanism 2 driven by motor unit
3.
[0004] Compressor mechanism 2 is detailed hereinafter. Cylinder
block 5, forming generally cylindrical cylinder 7, is equipped with
bearing 6 which rotatably supports shaft 4 and crosses with
cylinder 7 at approx. right angles. Bearing 6 is made of
aluminum-based material, i.e. non-magnetic material. Shaft 4 is
equipped with eccentric section 4a and inserted into bearing 6.
Rotor 14 is rigidly mounted to shaft 4.
[0005] Piston 9 slides in cylinder 7 and forms compressing chamber
10, and it is coupled to eccentric section 4a via connecting rod 8
which works as a linking means. Lubricating tube 11 is mounted to a
tip of eccentric section 4a.
[0006] Next, motor unit 3 is detailed hereinafter. Motor unit 3 is
a two-pole induction motor comprising stator 13 and rotor 14.
Stator 13 is formed by winding wires on a stator iron-core made of
laminated electromagnetic steel plates, and rotor 14 is formed of
rotor iron-core 15 having interior permanent-magnet 15b. Rotor
iron-core 15 has hollow bore 16 at its end face on compressor
mechanism 2 side, and bearing 6 extends into bore 16.
[0007] An operation of the foregoing conventional reciprocating
compressor is described hereinafter. Rotation of rotor 14 entails
shaft 4 to spin, and the rotation of eccentric section 4a of shaft
4 is transferred to piston 9 via connecting rod 8, so that piston 9
reciprocates in compressing chamber 10. This operation sucks
refrigerant gas supplied from a cooling system (not shown) into
compressing chamber 10, then compresses the gas, and discharges
successively the gas to the cooling system again such as a
refrigerator or an air-conditioner.
[0008] The rotation of shaft 4 causes lubricating tube 11 placed at
the lower end of shaft 4 to rotate, so that lubricant oil 12 is
drawn up by pumping operation due to the centrifugal force of tube
11. As a result, bearing 6, cylinder 7, connecting rod 8 and piston
9 are lubricated.
[0009] The foregoing structure; however, produces magnetic
attraction that attracts rotor 14 to a space of shorter distance if
the distance between rotor 14 and stator 13 is not uniform
(eccentric). In particular, when permanent magnet 15b built-in
rotor iron-core 15 is made of rare-earth material, i.e. the magnet
has intense magnetic force, the greater magnetic attraction is
produced at a greater eccentricity of the space.
[0010] As a result, shaft 4 inserted in bearing 6 slants and hits
against bearing 6. If shaft 4 rotates within bearing 6 in this
condition, the sliding faces of both bearing 6 and shaft 4 sometime
incur abrasion.
[0011] Another prior art of the foregoing conventional compressor
discloses a structure where an end-face of a main bearing made of
iron-based material is not laid over an end-face of a rotor iron
core on a compressor mechanism side. In this case, if bearing 6,
i.e. single-sided bearing, maintains the necessary bearing length,
a total length of shaft 4 is obliged to increase, which entails a
longer distance between bearing 6 and the gravity center of rotor
14. As a result, abrasion sometimes occurs on the sliding faces of
both bearing 6 and shaft 4. This is because the magnetic attraction
produced between rotor 14 and stator 13 works as strong moment
within bearing 6, so that shaft 4 hits more strongly against
bearing 6.
SUMMARY OF THE INVENTION
[0012] The present invention addresses the problems discussed
above, and aims to provide a highly reliable and efficient
compressor. The compressor of the present invention comprises the
following elements:
[0013] (a) a motor unit including a stator with windings, and a
rotor with a rotor iron-core and a permanent magnet;
[0014] (b) a compressor mechanism driven by the motor unit and
including the following sub-elements;
[0015] (b-1) a shaft including an eccentric shaft section, a main
shaft section and a sub shaft section, the main shaft section and
the sub shaft section sandwiching the eccentric shaft section
vertically and being placed coaxially;
[0016] (b-2) a cylinder block including a compressing chamber;
[0017] (b-3) a main bearing, disposed in the cylinder block such
that the main bearing crosses with an axial core of the compressing
chamber at right angles, for rotatably supporting the main shaft
section;
[0018] (b-4) a sub bearing, disposed in the cylinder block, for
rotatably supporting the sub shaft section;
[0019] (b-5) a piston for reciprocating in the compressing
chamber;
[0020] (b-6) a linking means for coupling the piston with the
eccentric shaft section; and
[0021] (c) an enclosed container for pooling lubricant oil and
accommodating the motor unit and the compressor mechanism.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 shows a vertical sectional view of a compressor in
accordance with a first exemplary embodiment of the present
invention.
[0023] FIG. 2 shows a vertical sectional view of a compressor in
accordance with a second exemplary embodiment of the present
invention.
[0024] FIG. 3 shows a vertical sectional view of a compressor in
accordance with a third exemplary embodiment of the present
invention.
[0025] FIG. 4 shows a vertical sectional view of a compressor in
accordance with a fourth exemplary embodiment of the present
invention.
[0026] FIG. 5 shows a vertical sectional view of a conventional
compressor.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0027] Exemplary embodiments of the present invention are
demonstrated hereinafter with reference to the accompanying
drawings.
Exemplary Embodiment 1
[0028] FIG. 1 shows a vertical sectional view of a compressor in
accordance with a first exemplary embodiment of the present
invention. In FIG. 1, enclosed container 101 accommodates
compressor mechanism 102 and motor unit 103 that drives the
compressor mechanism. The refrigerant filled in container 101 is a
hydrocarbon refrigerant such as R134a of which ozone-destroying
coefficient is zero (0), or R600a having a low global-warming
coefficient. Container 101 also pools lubricant oil 112 mutually
soluble with the refrigerant and having viscosity of 5-10 [cts] at
its bottom.
[0029] Next, compressor mechanism 102 is detailed hereinafter.
Shaft 104 includes eccentric shaft section 117, main-shaft section
116 and sub-shaft section 118. Main-shaft section 116 and sub-shaft
section 118 sandwich eccentric shaft section 117 vertically and are
disposed coaxially. Lubricating mechanism 111 formed on shaft 104
communicates into lubricant oil 112 at its first end and
communicates with the upper end of shaft 104 to open at its second
end.
[0030] Cylinder block 105 is made from cast-iron, and is integrally
formed of cylindrical compressing chamber 110 and main bearing 120
which rotatably supports main shaft section 116. Sub-bearing 121
rotatably supporting sub-shaft section 118 is fixed to cylinder
block 105. Piston 109 is inserted into compressing chamber 110 in a
slidable manner. Connecting rod 108 working as a linking means
couples piston 109 with eccentric shaft section 117.
[0031] Motor unit 103 is detailed hereinafter. It is an
inverter-driven motor formed of stator 113 and rotor 114, and
driven at any plural frequencies such as 30 Hz, 50 Hz, 70 Hz, and
80 Hz. Stator 113 is constructed as this: a plurality of teeth 113b
radially formed is disposed at iron core 113a, and windings 113d
are provided to teeth 113b via insulating material 113c to form a
motor of a concentrated winding structure. Rotor 114 is fixed to
main-shaft section 116 of shaft 104 and includes permanent magnet
115a built in rotor iron-core 115. Permanent magnet 115a is made
of, e.g. rare-earth magnet such as neodymium, iron, boron-based
ferromagnetic materials.
[0032] Assume that there is a virtual plane which includes end
section 115b of rotor iron-core 115 on the compressor mechanism
side and is generally orthogonal to the axial core of main shaft
section 116. Main bearing 120 is structured so as not to cross with
this virtual plane.
[0033] An operation of the compressor discussed above is
demonstrated hereinafter. When a current runs through stator 113,
rotor 114 spins shaft 104, and eccentric motion of eccentric shaft
section 117 is transferred to piston 109 via connecting rod 108,
thereby reciprocating piston 109 in compressing chamber 110. This
operation sucks the refrigerant gas from the cooling system (not
shown) to chamber 110, and compresses the gas, then discharges the
gas to the cooling system again.
[0034] Lubricating mechanism 111 formed on shaft 104 pumps up
lubricant oil 112, which is then discharged from an upper end of
shaft 104.
[0035] Permanent magnet 115a built in rotor iron-core 115 is made
of, e.g. rare-earth material having intense magnetic force, so that
it produces extraordinary intense magnetic attraction at a place
where a distance between rotor 114 and stator 113 is small.
[0036] However, when shaft 104 of this structure receives an
unbalanced load caused by the magnetic attraction generated between
rotor 114 and stator 113, a distance between two fulcrums is
approx. doubled comparing with the conventional structure discussed
previously. Because in the case of the conventional structure, the
single-sided bearing receives the unbalanced load at its upper and
lower ends as the fulcrums arranged in the diagonal direction with
respect to the center axis of shaft 104 placed in the inner wall of
the main bearing. On the other hand, a double-sided bearing
employed in the structure of the first embodiment receives the
unbalanced load at its inner wall end on the counter side to the
sub-bearing and at an inner wall end of the sub-bearing on the
counter side to the main bearing along a diagonal direction with
respect to the axis center of shaft 104.
[0037] The extension of the distance between the fulcrums reduces a
slant angle of shaft 104 within the bearing, so that shaft 104
scarcely hits against the bearing. As a result, sliding loss due to
the hitting can be prevented and the compressor can maintain
efficient operation. At the same time, a sliding noise due to the
hitting can be suppressed, so that a compressor with a lower noise
is obtainable. The load to shaft 104 in operation is received at
eccentric shaft section 117 (fulcrum) as a center, to which a
compressing load from piston 109 is applied, and upper and lower
ends, so that the load can be distributed generally even to this
fulcrum. Comparing with the single-sided bearing, in which the load
concentrates on its one end, the sliding face of shaft 104 has
better reliability.
[0038] Shaft 104 receives the load in operation at its wide area
with little interference with the bearing, so that contact pressure
of main bearing 120 and sub bearing 121 lowers, which can shorten
the length of main bearing 120. As a result, the total height of
the compressor can be lowered. Further, a reduction of the sliding
length can lower viscosity resistance at the sliding section, so
that the efficiency is improved.
[0039] Main bearing 120 is integrally formed with cylinder bock
105, i.e. made of cast-iron that is iron-based material, however,
since bearing 120 is placed so as not to touch at rotor iron-core
115, the magnetic flux of permanent magnet 115a built in iron-core
115 seldom interferes with main bearing 120. As a result,
eddy-current loss scarcely occurs in the main bearing, and the
higher efficiency can be expected.
[0040] Motor unit 103 is inverter-driven, so that it is driven at a
high frequency such as 70-80 Hz in response to the load. At that
time, motor unit 103 produces strong magnetic attraction, which
tends to slant shaft 104; however, since shaft 104 is supported by
the double-sided bearing, i.e. main bearing 120 and sub bearing
121, shaft 104 is prevented from slanting, and at the same time,
sliding loss can be reduced. As a result, the compressor can
maintain efficient operation, and prevent the shaft from hitting
against the bearing, so that the reliability can be improved.
[0041] When motor unit 103 is driven at a low frequency such as 30
Hz, the double-sided bearing structure prevents shaft 104 from
slanting because shaft 104 is supported by main bearing 120 and sub
bearing 121, so that the sliding loss can be reduced. Thus use of
lubricant oil 112 of low viscosity such as 5-10 [cts] can assure
the reliability.
[0042] Stator 113 includes plural teeth 113b radially formed in
iron-core 113a, and windings are provided to teeth 113b via
insulating member 113c. This structure eliminates a coil-end which
is needed in the distributed winding structure. As a result, the
total heights of stator 113 and rotor 114 can be lowered, so that
the total height of the compressor can be further lowered. The low
profile of stator 113 and rotor 114 facilitates uniforming the
clearance between stator 113 and rotor 114. As a result, the
magnetic attraction rarely occurs, so that an increase of an input
current due to interference between stator 113 and rotor 114 as
well as an increase of a noise can be avoided.
[0043] In this embodiment, connecting rod 108 is used as the
linking means for coupling the piston with the eccentric shaft;
however, a ball joint or a Scotch yoke can be used as the linking
means.
Exemplary Embodiment 2
[0044] FIG. 2 shows a vertical sectional view of a compressor in
accordance with the second exemplary embodiment of the present
invention. Similar elements to those in the first embodiment have
the same reference marks, and the detailed descriptions thereof are
omitted here. In FIG. 2, motor unit 203 is a two-pole synchronous
motor comprising the following elements:
[0045] stator 213 formed of a stator iron-core wound with windings,
the iron-core being formed by laminating electromagnetic steel
sheets, and
[0046] rotor 214 formed of rotor iron-core 215 equipped with a
secondary conductor, iron-core 215 being formed by laminating
electromagnetic steel sheet.
[0047] Rotor iron-core 215 incorporates permanent magnet 215a made
of, e.g. neodymium of rare-earth magnet, iron, boron-based
ferromagnetic materials. Other structures remain unchanged as the
first embodiment.
[0048] An operation of the foregoing compressor is demonstrated
hereinafter. Motor unit 203 starts working as an induction motor,
and when it comes around the synchronizing rpm, synchronous pull-in
is carried out for synchronous operation.
[0049] Since permanent magnet 215a is made of ferromagnetic
material having intense magnetic force, it produces extraordinary
intense magnetic attraction at the place where a clearance between
rotor 214 and stator 213 is small. However, the same structure as
that in the first embodiment can overcome this problem. As a
result, highly efficient operation of the synchronous motor is
advantageously used for obtaining high energy efficiency. At the
same time, the shaft of the compressor is prevented from hitting
the bearing due to slant, so that the reliability can be
improved.
Exemplary Embodiment 3
[0050] FIG. 3 shows a vertical sectional view of a compressor in
accordance with the third exemplary embodiment of the present
invention. Similar elements to those in the first embodiment have
the same reference marks, and the detailed descriptions thereof are
omitted here.
[0051] In FIG. 3, enclosed container 101 accommodates compressor
mechanism 302 and motor unit 303 that drives this compressor
mechanism. Cylinder block 305 of compressor mechanism 302 is made
from cast-iron and forms cylindrical compressing chamber 110. Main
bearing 320 for rotatably supporting main shaft section 116 of
shaft 104 and sub-bearing 121 for rotatably supporting sub-shaft
section 118 are rigidly mounted to cylinder block 305.
[0052] Motor unit 303 comprising stator 113 and rotor 314 is an
inverter-driven motor that is driven at plural frequencies. Rotor
314 is fixed to main-shaft section 116 of shaft 104 and includes
permanent magnet 315a built in rotor iron-core 315. Permanent
magnet 315a is made of, e.g. rare-earth magnet such as neodymium,
iron, boron-based ferromagnetic materials. Rotor iron-core 315 has
hollow bore 306 at its end face on compressor mechanism 302 side.
Main bearing 320 is made from aluminum alloy which is non-magnetic
material, and extends into bore 306.
[0053] An operation of the foregoing compressor is described
hereinafter. When a current runs into stator 113, rotor 314 spins
shaft 104, and eccentric motion of eccentric shaft section 117 is
transferred to piston 109 via connecting rod 108, so that piston
109 reciprocates in compressing chamber 110. This operation sucks
refrigerant gas supplied from a cooling system (not shown) into
compressing chamber 110, then compresses the gas, and discharges
the gas into the cooling system again. Lubricating mechanism 111
formed on shaft 104 pumps up lubricant oil 112, which is then
discharged from an upper end of shaft 104.
[0054] Permanent magnet 315a built in rotor iron-core 315 is made
of, e.g. rare-earth material having intense magnetic force, so that
it produces extraordinary intense magnetic attraction at a place
where a clearance between rotor 314 and stator 113 is small.
[0055] When shaft 104 of this structure receives an unbalanced load
caused by the magnetic attraction generated between rotor 314 and
stator 113, a distance between two fulcrums becomes far longer than
that of the conventional structure discussed previously. On top of
that, since main bearing 320 extends into bore 306, the distance
between the fulcrums becomes further longer. Because in the case of
the conventional structure, the single-sided bearing receives the
unbalance load at its upper and lower ends as fulcrums arranged in
the diagonal direction with respect to the center axis of shaft 104
placed in the inner wall of the main bearing. On the other hand,
the double-sided bearing employed in this third embodiment receives
the unbalanced load at the following two fulcrums: its inner wall
end on the counter side to the sub-bearing and at an inner wall end
of the sub-bearing on the counter side to the main bearing along a
diagonal direction with respect to the axis center of shaft
104.
[0056] The extension of the distance between the fulcrums reduces a
slant angle of shaft 104 within the bearing, so that shaft 104
scarcely hits against the bearing. As a result, sliding loss due to
the hitting can be prevented and the compressor can maintain
efficient operation. At the same time, a sliding noise due to the
hitting can be suppressed, so that a compressor with a lower noise
is obtainable. The load to shaft 104 in operation is received at
eccentric bearing 117 (fulcrum) as a center, to which a compressing
load from piston 109 is applied, and upper and lower ends, so that
the load can be distributed generally even to this fulcrum. In
comparison with the single-sided bearing, in which the load
concentrates on its one end, the sliding face of shaft 104 has
better reliability.
[0057] Since main bearing 320 is made of aluminum alloy, i.e.
non-magnetic material, permanent magnet 315a built in rotor
iron-core 315 does not produce eddy-current. Thus eddy-current loss
can be eliminated, and high efficiency can be achieved.
[0058] Motor unit 303 is inverter-driven, so that it is driven at a
high frequency in response to the load. At that time, motor unit
303 produces strong magnetic attraction, which tends to slant shaft
104; however, since shaft 104 is supported by the double-sided
bearing, i.e. main bearing 320 and sub bearing 121, shaft 104 is
prevented from slanting, and at the same time, sliding loss can be
reduced. As a result, the compressor can maintain efficient
operation, and prevent the shaft from hitting against the bearing,
so that the reliability can be improved.
[0059] Stator 113 includes plural teeth 113b radially formed in
iron-core 113a, and windings 113d are provided to teeth 113b via
insulating member 113c. This structure eliminates a coil-end which
is needed in the distributed winding structure. As a result, total
heights of stator 113 and rotor 314 can be lowered, so that the
total height of the compressor can be further lowered. The low
profile of stator 113 and rotor 314 facilitates uniforming the
clearance between stator 113 and rotor 314, and as a result, the
magnetic attraction rarely occurs, so that an increase of an input
current due to interference as well as an increase of noise can be
avoided.
Exemplary Embodiment 4
[0060] FIG. 4 shows a vertical sectional view of a compressor in
accordance with the fourth exemplary embodiment of the present
invention. Similar elements to those in the third embodiment have
the same reference marks, and the detailed descriptions thereof are
omitted here.
[0061] In FIG. 4, motor unit 403 is a two-pole synchronous motor
comprising the following elements:
[0062] stator 213 formed of a stator iron-core wound with windings,
the iron-core being formed by laminating electromagnetic steel
sheets, and
[0063] rotor 414 formed of rotor iron-core 415 equipped with a
secondary conductor, iron-core 415 being formed by laminating
electromagnetic steel sheets,
[0064] Rotor iron-core 415 incorporates permanent magnet 415a made
of, e.g. neodymium of rare-earth magnet, iron, boron-based
ferromagnetic materials. Other structures remain unchanged as the
third embodiment.
[0065] An operation of the foregoing compressor is demonstrated
hereinafter. Motor unit 403 starts working as an induction motor,
and when it comes near the synchronizing rpm, synchronous pull-in
is carried out for synchronous operation. Since permanent magnet
415a is made of ferromagnetic material having intense magnetic
force, it produces extraordinary intense magnetic attraction at the
place where a clearance between rotor 414 and stator 213 is
small.
[0066] However, the same structure as that in the third embodiment
can overcome this problem. As a result, highly efficient operation
of the synchronous motor is advantageously used for obtaining high
energy efficiency. At the same time, the shaft of the compressor is
prevented from hitting the bearing caused by the slant, so that the
reliability can be improved.
* * * * *