U.S. patent application number 13/222191 was filed with the patent office on 2012-03-08 for motor-driven compressor.
This patent application is currently assigned to KABUSHIKI KAISHA TOYOTA JIDOSHOKKI. Invention is credited to Hiroshi Fukasaku, Takahiro Hoshida, Kensuke Ikai, Takayuki Kato, Minoru Mera, Takahiro Sugioka.
Application Number | 20120057999 13/222191 |
Document ID | / |
Family ID | 45595624 |
Filed Date | 2012-03-08 |
United States Patent
Application |
20120057999 |
Kind Code |
A1 |
Fukasaku; Hiroshi ; et
al. |
March 8, 2012 |
MOTOR-DRIVEN COMPRESSOR
Abstract
The motor-driven compressor includes a housing, a compression
mechanism, a rotary shaft and an electric motor all disposed in the
housing, a protective film and a fixing resin. The electric motor
is adapted to rotate the rotary shaft thereby to drive the
compression mechanism. The electric motor has a rotor fixed on the
rotary shaft and a stator supported by the housing. The rotor has a
permanent magnet and a magnet hole in which the permanent magnet is
inserted. The magnet hole extends in an axial direction of the
rotor. The protective film is formed on a surface of the permanent
magnet for improving corrosion resistance of the permanent magnet.
The fixing resin is filled in at least part of a gap between the
permanent magnet and a wall of the magnet hole for fixing the
permanent magnet to the wall of the magnet hole.
Inventors: |
Fukasaku; Hiroshi;
(Aichi-ken, JP) ; Mera; Minoru; (Aichi-ken,
JP) ; Ikai; Kensuke; (Aichi-ken, JP) ; Kato;
Takayuki; (Aichi-ken, JP) ; Sugioka; Takahiro;
(Aichi-ken, JP) ; Hoshida; Takahiro; (Aichi-ken,
JP) |
Assignee: |
KABUSHIKI KAISHA TOYOTA
JIDOSHOKKI
Aichi-ken
JP
|
Family ID: |
45595624 |
Appl. No.: |
13/222191 |
Filed: |
August 31, 2011 |
Current U.S.
Class: |
417/410.1 |
Current CPC
Class: |
H02K 15/03 20130101;
H02K 1/276 20130101; F04B 35/04 20130101; H02K 15/12 20130101 |
Class at
Publication: |
417/410.1 |
International
Class: |
F04B 35/04 20060101
F04B035/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 6, 2010 |
JP |
2010-199283 |
Claims
1. A motor-driven compressor comprising: a housing having a suction
port and a discharge port; a compression mechanism disposed in the
housing, the compression mechanism being adapted to compress
refrigerant drawn into the housing through the suction port and to
discharge the compressed refrigerant out of the housing through the
discharge port; a rotary shaft disposed in the housing; an electric
motor disposed in the housing, the electric motor being adapted to
rotate the rotary shaft thereby to drive the compression mechanism,
the electric motor having a rotor fixed on the rotary shaft and a
stator supported by the housing, the rotor having a permanent
magnet and a magnet hole in which the permanent magnet is inserted,
the magnet hole extending in an axial direction of the rotor; a
protective film formed on a surface of the permanent magnet for
improving corrosion resistance of the permanent magnet; and a
fixing resin filled in at least part of a gap between the permanent
magnet and a wall of the magnet hole for fixing the permanent
magnet to the wall of the magnet hole.
2. The motor-driven compressor according to claim 1, wherein the
magnet hole has a main hole corresponding in shape to a contour of
the permanent magnet and an expanded hole expanded outward from
part of a wall of the main hole, wherein the expanded hole is
opened at least at one end thereof in the axial direction of the
rotor and filled with the fixing resin.
3. The motor-driven compressor according to claim 1, wherein the
protective film formed on the surface of the permanent magnet has a
chemical adsorption film having at least one of hydroxy group and
amino group.
4. The motor-driven compressor according to claim 1, wherein the
protective film formed on the surface of the permanent magnet has a
film made of a metal.
5. The motor-driven compressor according to claim 1, wherein the
protective film formed on the surface of the permanent magnet has a
film made of a resin.
6. The motor-driven compressor according to claim 1, wherein the
permanent magnet is a rare-earth magnet.
7. The motor-driven compressor according to claim 1, wherein the
motor-driven compressor is used for a vehicle-mounted air
conditioner having a refrigerant circulation path in which a
nonmetallic duct is connected.
8. The motor-driven compressor according to claim 1, wherein the
motor-driven compressor is used in a refrigeration system through
which the refrigerant that is expressed by molecular formula of
C.sub.3H.sub.mF.sub.n having one double bond in a molecular
structure of the molecular formula, wherein m is an integral number
of 1 to 5, n is an integral number of 1 to 5, and m+n=6, or a mixed
refrigerant containing the refrigerant circulates.
9. The motor-driven compressor according to claim 1, wherein the
housing has therein lubricating oil containing at least one of
polyolester (POE), polyvinyl ether (PVE) and polyalkylene glycol
(PAG).
10. The motor-driven compressor according to claim 1, wherein the
rotor has a rotor body and a pair of end plates, the magnet hole of
the rotor extending through the rotor body in an axial direction of
the rotor body, the paired end plates being disposed at opposite
ends in the axial direction of the rotor body for closing the
magnet hole.
11. The motor-driven compressor according to claim 10, wherein an
entire outer surface of the rotor is coated with a resin film.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a motor-driven compressor
for use in a refrigeration system.
[0002] Motor-driven compressor for use in a refrigeration system
such as vehicle-mounted air conditioner has in the housing thereof
an electric motor that drives the compression mechanism of the
compressor. The housing of the compressor forms a refrigerant
circulation path through which refrigerant circulates and the
electric motor has therein a permanent magnet such as ferrite
magnet or rare-earth magnet. Thus, the permanent magnet is exposed
to an environment where the permanent magnet is contactable with
the refrigerant and lubricating oil circulating through the
refrigerant circulation path of the refrigeration system. The
permanent magnet is relatively deteriorative in the presence of
water or acid. The deterioration of the permanent magnet leads to
the deterioration of the entire motor-driven compressor. To prevent
the deterioration of the permanent magnet, Japanese Patent
Application Publication No. 2009-225636 proposes forming a
protective film on the surface of the permanent magnet incorporated
in the electric motor of the motor-driven compressor for improving
the corrosion resistance of the permanent magnet.
[0003] The use of the protective film is effective in preventing
the deterioration of the permanent magnet. However, if the
protective film has any damage, the effect of protection by the
film is reduced. The damage of the protective film is attributed to
the fact that the permanent magnet in the rotor is urged to repeat
slight movement (or vibration) relative to the rotor body while the
motor-driven compressor is in operation. In view of the fact that
the permanent magnet is attracted firmly against the rotor body by
the magnetic force, it is unlikely that the permanent magnet moves
relative to the rotor body. However, it is considered that various
factors such as external vibrations cause the slight movement of
the permanent magnet relative to the rotor body while the
motor-driven compressor is actually in operation.
[0004] The present invention is directed to a motor-driven
compressor that prevents the permanent magnet incorporated in an
electric motor from moving relative to the rotor body of the rotor
thereby to maintain the soundness of the protective film formed on
the surface of the permanent magnet and to reduce deterioration of
the permanent magnet.
SUMMARY OF THE INVENTION
[0005] In accordance with an aspect of the present invention, the
motor-driven compressor includes a housing, a compression
mechanism, a rotary shaft, an electric motor, a protective film and
a fixing resin. The housing has a suction port and a discharge
port. The compression mechanism is disposed in the housing and
adapted to compress refrigerant drawn into the housing through the
suction port and to discharge the compressed refrigerant out of the
housing through the discharge port. The rotary shaft is disposed in
the housing. The electric motor is disposed in the housing. The
electric motor is adapted to rotate the rotary shaft thereby to
drive the compression mechanism. The electric motor has a rotor
fixed on the rotary shaft and a stator supported by the housing.
The rotor has a permanent magnet and a magnet hole in which the
permanent magnet is inserted. The magnet hole extends in an axial
direction of the rotor. The protective film is formed on a surface
of the permanent magnet for improving corrosion resistance of the
permanent magnet. The fixing resin is filled in at least part of a
gap between the permanent magnet and a wall of the magnet hole for
fixing the permanent magnet to the wall of the magnet hole.
[0006] Other aspects and advantages of the invention will become
apparent from the following description, taken in conjunction with
the accompanying drawings, illustrating by way of example the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The invention together with objects and advantages thereof,
may best be understood by reference to the following description of
the presently preferred embodiments together with the accompanying
drawings in which:
[0008] FIG. 1 is a partially cross sectional view showing a
motor-driven compressor according to a first example of the present
invention;
[0009] FIG. 2 is an exploded perspective view showing a rotor of
the motor-driven compressor of FIG. 1;
[0010] FIG. 3 is an end view showing a rotor body of the rotor of
FIG. 1, wherein permanent magnets are yet to be inserted in the
rotor body;
[0011] FIG. 4 is an end view showing the rotor body of FIG. 3,
wherein the permanent magnets have been inserted in the rotor
body;
[0012] FIG. 5 is an illustration showing a method for filling
expanded holes of the magnet holes in the rotor body of FIG. 4 with
fixing resin;
[0013] FIG. 6 is an illustration showing one of the permanent
magnets fixed by the fixing resin in the rotor body of FIG. 4;
[0014] FIG. 7 is a perspective view showing the assembled rotor of
the motor-driven compressor of FIG. 1;
[0015] FIG. 8 is a schematic view showing a vehicle-mounted air
conditioner according to the first example of the present
invention; and
[0016] FIG. 9 is a perspective view showing a rotor of a
motor-driven compressor according to a second example of the
present invention being coated with resin film by spraying.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0017] The following will describe the motor-driven compressor
according to the first example of the present invention with
reference to FIGS. 1 through 8. Referring to FIG. 1, the
motor-driven compressor 1 includes a housing 10, a compression
mechanism 15, a rotary shaft 21 and an electric motor 2 all
disposed in the housing 10. The housing 10 has therein a suction
port 11 and a discharge port 12. The compression mechanism 15 is
adapted to compress refrigerant drawn into the housing 10 through
the suction port 11 and to discharge the compressed refrigerant out
of the housing 10 through the discharge port 12. The electric motor
2 rotates the rotary shaft 21 thereby to drive the compression
mechanism 15.
[0018] The compression mechanism 15 has a fixed scroll member 13
fixed in the housing 10 and a moving scroll member 14 disposed in
facing relation to the fixed scroll member 13. The fixed scroll
member 13 and the moving scroll member 14 have therebetween a
plurality of compression chambers 150 whose volumes are variable
for compressing refrigerant. The moving scroll member 14 is
connected to an eccentric pin 210 of the rotary shaft 21 via a
bearing 216 and an eccentric bushing 215 so as to make an orbital
motion in accordance with the rotation of the rotary shaft 21
thereby to vary the volumes of the compression chambers 150.
[0019] The electric motor 2 has a rotor 22 and a stator 23 disposed
surrounding the rotor 22. The rotor 22 has therethrough a central
hole 229 in which the rotary shaft 21 is fixed. The rotary shaft 21
projects at the opposite ends thereof from the rotor 22 and is
rotatably supported at the opposite ends by bearings 41 and 42 in
the housing 10, respectively. The stator 23 is supported by the
housing 10 and provided with a coil 235. When the coil 235 is
energized, the rotor 22 having therein a plurality of permanent
magnets 3 is rotated. In the present example, the rotor 22 has four
permanent magnets 3.
[0020] Referring to FIG. 2, the rotor 22 is formed of a plurality
of magnetic steel plates laminated together into a cylinder shape.
The rotor 22 has a rotor body 220 through which a plurality of
magnet holes 225 are formed extending axially and a pair of end
plates 25 disposed at the opposite ends in the axial direction of
the rotor body 220. The paired end plates 25 close the magnet holes
225.
[0021] Each permanent magnet 3 is inserted in the magnet hole 225.
The permanent magnet 3 has on the surface thereof a protective film
35 that improves the corrosion resistance of the permanent magnet
3. The protective film 35 has a chemical adsorption film. A known
neodymium magnet (or rare-earth magnet) having neodymium (Nd), iron
(Fe) and boron (B) as the major components is used as the permanent
magnet 3.
[0022] Although a film made of a metal or any other protective
films are usable as the protective film 35, the chemical adsorption
film is used in the present example. After the surface of the
permanent magnet 3 is cleaned by removing foreign substance from
the surface of the permanent magnet 3, a film forming that forms
the chemical adsorption film is performed.
[0023] The film forming is accomplished by bringing the permanent
magnet 3 into contact with film forming solution that is alkaline
aqueous solution whose pH is 8 to 10 and then drying. More
specifically, the film forming solution is prepared so that the pH
becomes about 8 by adding three weight percentages (wt %) of
triethanolamine and one weight percentage (wt %) of polyoxyalkylene
alkyl ether that serves as a surfactant to one liter of water.
[0024] Then, the film forming solution is heated to about 60
degrees Celsius (.degree. C.) and the permanent magnet 3 is
immersed in the heated film forming solution for three minutes. The
permanent magnet 3 is removed from the alkaline aqueous solution
and kept in an oven under an air atmosphere of about 100.degree. C.
for sixty minutes. The permanent magnet 3 is removed from the oven
and left as it is until its temperature reaches an ordinary
temperature. Thus, the chemical adsorption film containing an amino
group is formed on the surface of the permanent magnet 3. The
resulting chemical adsorption film has a molecular level
thickness.
[0025] Each permanent magnet 3 having the chemical adsorption film
(protective film 35) is inserted in the magnet hole 225 as
described above. As shown in FIGS. 5 and 6, at least part of the
gap between the permanent magnet 3 and the wall of the magnet hole
225 is filled with fixing resin 6. More specifically, as shown in
FIG. 3, each magnet hole 225 has a generally rectangular main hole
228 corresponding in shape to the contour of the permanent magnet 3
and a pair of expanded holes 227 each expanded outward from part of
the short side of the rectangular main hole 228. Each expanded hole
227 extends axially through the rotor body 220. In the present
example, each expanded hole 227 is filled with the fixing resin 6
as shown in FIGS. 5 and 6.
[0026] Although various methods may be used for filling the
expanded holes 227 with the fixing resin 6, the following method is
used for the present example. As shown in FIGS. 2 through 4, each
permanent magnet 3 whose entire surface is coated with the
protective film 35 is inserted into the magnet hole 225 of the
rotor body 220 having the paired elongated holes 227. Then, a
syringe-like resin filling device 7 having a needle member 71 with
an injection hole 710 at the distal end thereof is prepared, as
shown in FIG. 5.
[0027] The resin filling device 7 has a cylindrical member 72 whose
interior communicates with that of the needle member 71 and a
piston member 73 that pushes the fixing resin 6 out of the
cylindrical member 72. Resin filling operation is performed by
inserting the needle member 71 of the resin filling device 7 into
the expanded holes 227 of the magnet hole 225 and then injecting a
proper amount of the fixing resin 6 into the expanded holes 227, as
shown in FIG. 5. In the present example, the fixing resin 6 is not
filled in each expanded hole 227 throughout its axial length, but
partially filled in the expanded hole 227 at locations spaced
axially. In order that all the permanent magnets 3 are fixed at the
opposite ends in the width direction thereof, the fixing resin 6 is
filled in all the expanded holes 227. Epoxy-series resin is used as
the fixing resin 6. It is noted that although in the present
example the fixing resin 6 is partially filled in the expanded hole
227 at locations spaced axially, the fixing resin 6 may be filled
in the expanded hole 227 throughout the axial length.
[0028] As indicated in FIG. 2, with the permanent magnets 3 having
the chemical adsorption film fixed in the respective magnet holes
225 in the rotor body 220 and also the end plates 25 disposed in
place on the opposite ends of the rotor body 220, rivets 44 are
inserted through rivet holes 224, 254 of the rotor body 220 and the
end plates 25, respectively, and one end of each rivet 44 (or the
left end as seen in FIG. 2) is crimped thereby to fix the end
plates 25 to the rotor body 220. Thus, the rotor 22 is completed.
In addition, the rotary shaft 21 is inserted through the central
hole 229 of the rotor body 220 and the central holes 259 of the end
plates 25 and fixed.
[0029] In the present example, the motor-driven compressor 1 is
used for a vehicle-mounted air conditioner 5, as shown in FIG. 8.
The air conditioner 5 includes a condenser 51, a receiver 52, an
expansion valve 53 and an evaporator 54. The compressor 1, the
condenser 51, the receiver 52, the expansion valve 53 and the
evaporator 54 are connected in this order in the refrigerant
circulation path 55 of the air conditioner 5. The expansion valve
53 is adjusted to change its opening by a controller 57 in
accordance with the refrigerant temperature measured by a
temperature sensor 56 located downstream of the evaporator 54.
[0030] The receiver 52 separates the refrigerant into vapor and
liquid and transfers only the liquid refrigerant to the expansion
valve 53. In addition, the receiver 52 removes water contained in
the refrigerant by adsorption agent (not shown) provided in the
receiver 52. The refrigerant circulation path 55, or the
motor-driven compressor 1, is filled sealingly with
2,3,3,3-tetrafluoro-1-propene (CF.sub.3--CF.dbd.CH.sub.2) as a
refrigerant and polyolester as a lubricating oil, respectively.
Resin duct that is a nonmetallic duct is used in the part of the
duct forming the refrigerant circulation path 55.
[0031] When the air conditioner 5 is operated for a long period of
time, water may permeate through the resin duct forming a part of
the refrigerant circulation path 55 and gradually enters the
refrigerant circulation path 55. In addition, refrigerant or
lubricating oil may change its properties by the reaction with
water thereby to produce acid. In the present example, as described
above, at least part of the gap between the permanent magnet 3 and
the wall of the magnet hole 225 is filled with the fixing resin 6
after the protective film 35 is formed on the surface of the
permanent magnet 3 incorporated in the rotor 22. By so doing, if
the permanent magnet 3 in the rotor 22 is urged to move relative to
the rotor body 220 for any reason while the motor-driven compressor
1 is in operation, the permanent magnet 3 is prevented from moving
by the fixing resin 6 present in each expanded hole 227. Thus, the
protective film 35 on the surface of the permanent magnet 3 is
prevented from being damaged, so that the lifetime of the sound
protective film 35 is increased and the deterioration of the
permanent magnet 3 is prevented, accordingly.
[0032] The following will describe the motor-driven compressor
according to the second example of the present invention with
reference to FIG. 9. In the present example, the rotor 22 of the
first example is further improved. That is, in the present example,
the entire outer surface of the rotor 22 is coated with film made
of resin or resin film 27 as shown in FIG. 9. The resin film 27 is
formed by coating 270 sprayed by spray units 275. Fluorine-series
resin is used as the resin film 27. The resin film 27 is formed so
as to coat not only the rotor 22 but also part of the rotary shaft
21 and the visible boundaries between the rotary shaft 21 and the
rotor 22.
[0033] In the present example, as described in the first example,
the rotor 22 includes the rotor body 220 having therethrough the
magnet holes 225, the permanent magnets 3 inserted in the magnet
holes 225, and the end plates 25 closing the openings of the magnet
holes 225. That is, the openings of the magnet holes 225 having
therein the permanent magnets 3 are closed by the end plates 25, so
that the magnet holes 225 are tentatively closed. Thus, with the
exception that water or acid permeates through minute opening
present in the rotor body 220 or minute gap between the rotor body
220 and the end plates 25, direct ingress of water or acid into the
magnet holes 225 with refrigerant and lubricating oil is
prevented.
[0034] In addition, the resin film 27 that coats the entire outer
surface of the rotor 22 prevents water or acid from permeating
through the above minute opening or gap with refrigerant and
lubricating oil. Therefore, the ingress of water or acid into the
magnet holes 225 is prevented and the deterioration of the
permanent magnet 3 is further prevented, accordingly.
[0035] If water or acid enters the magnet hole 225, the protective
film 35 that is maintained in a sound state prevents the
deterioration of the permanent magnet 3. In addition, if the
permanent magnet 3 becomes brittle and is powdered by chemical
reaction with water, acid, or hydrogen derived therefrom for any
reason, the closed structure where the rotor body 220 and the end
plates 25 are combined together and an additional closed structure
where the resin film 27 coats the minute opening and the minute gap
cooperate to prevent the magnet powder from being released from the
rotor 22.
[0036] The motor-driven compressor of the present example provides
effective measures against the circumstance under which the
permanent magnet 3 is deteriorative and the deterioration of the
permanent magnet 3, and also a measure against the permanent magnet
3 that has been deteriorated. Thus, the second example provides the
motor-driven compressor with a high reliability.
[0037] In the motor-driven compressor of the present invention, it
is preferred that the magnet hole has a main hole corresponding in
shape to the contour of the permanent magnet and an expanded hole
expanded outward from part of the wall of the main hole. It is also
preferred that the expanded hole is opened at least at one end
thereof in the axial direction of the rotor and filled with the
fixing resin. In this case, the main hole of the magnet hole should
be of a minimum required size, so that the filling of the fixing
resin is concentrated in the expanded hole. Thus, the resin filling
operation is facilitated while minimizing the deterioration of
magnetic performance due to the formation of the expanded hole in
the rotor for filling the fixing resin.
[0038] For the resin filling operation, a syringe-like resin
filling device having a needle member with an injection hole at the
distal end thereof may be used. The resin filling operation is
accomplished by inserting the needle member into the expanded hole
after inserting the permanent magnet into the magnet hole. The gap
between the magnet hole and the permanent magnet may be filled at
any position with the fixing resin without forming the expanded
hole.
[0039] Various kinds of film may be used as the protective film to
be formed on the surface of the permanent magnet as long as the
protective film improves the corrosion resistance of the permanent
magnet. The protective film formed on the surface of the permanent
magnet may have a chemical adsorption film having at least one of
hydroxy group and amino group.
[0040] The chemical adsorption film blocks the active spot from
which the corrosion of the surface of the permanent magnet starts,
thereby to prevent the development of the corrosion. In addition,
the chemical adsorption film has an effect to neutralize acid by
allowing alkaline functional group, such as hydroxy group or amino
group of the chemical adsorption film, to react with acid. That is,
the chemical adsorption film offers anti-corrosion and neutralizing
effects. Thus, even if acid is present in the refrigerant
circulation path, the permanent magnet having the chemical
adsorption film is not prone to corrode and has high
durability.
[0041] The chemical adsorption film can be easily made by allowing
the permanent magnet having a desired shape to be in contact with
the alkaline aqueous solution which contains amines and/or hydroxys
and whose pH is 8 to 10, and then drying the film forming solution
on the permanent magnet. That is, the resistance of the permanent
magnet against acid corrosion is improved by allowing the permanent
magnet to be in contact with the film forming solution and drying
the film forming solution on the permanent magnet.
[0042] The chemical adsorption film is formed by chemical
adsorption of amino group, hydroxy group or chemical compound
containing amino group and hydroxy group on the surface of the
permanent magnet. It is noted that the amino group may be defined
as monovalent functional group (--NH.sub.2, --NHR, --NRR') wherein
one or more hydrogen atoms are removed from ammonia, primary amine
or secondary amine. This definition does not intend to restrict the
material of the amino group but to provide the structure of the
amino group. The amino group includes monovalent functional group
obtained from tertiary amine.
[0043] The component of the chemical adsorption film depends on
amines and/or hydroxys contained in film forming solution used in
the film forming. The chemical adsorption film may have a
composition of hydroxy group only, amino group only or both of
hydroxy group and amino group.
[0044] The chemical adsorption film is formed of any one of the
above functional groups or chemical compound having such functional
group that is chemically adsorbed on a molecular level. Thus, the
chemical adsorption film is extremely thin. The confirmation for
the presence of the chemical adsorption film may be accomplished by
performing method such as Raman spectroscopic analysis,
infrared-ray spectroscopic analysis, or secondary ion mass
spectrometry (SIMS) for confirming the presence of amino group or
hydroxy group.
[0045] The protective film formed on the surface of the permanent
magnet may have a film made of a metal. The metal for the
protective film includes aluminum, nickel and copper. Known method
such as plating, sputtering or evaporation may be used for forming
a metal film. The corrosion resistance of the permanent magnet is
improved remarkably by using a film made of a metal as the
protective film. Film made only of a metal may be used as the
protective film. Alternatively, the chemical adsorption film may be
formed on the surface of the film made of a metal. In this case,
the combined effects of the metal film and the chemical adsorption
film synergistically enhance the corrosion resistance of the
permanent magnet. To prevent the deterioration of the electric
motor, a film made of a magnetic metal such as nickel is preferably
used as the film made of a metal.
[0046] The protective film formed on the surface of the permanent
magnet may have a film made of a resin. The resin for the film
includes epoxy resin, acrylic resin and fluorine resin. The resin
film may be formed by various coating methods. Using a film made of
a resin as the protective film, hydrophobic surface that is prone
to repel water may be easily formed. Although a film made only of a
resin may be used as the protective film, the film made of a resin
may be combined with the chemical adsorption film and/or the film
made of a metal in a laminar form. For example, the chemical
adsorption film may be formed on the surface of the resin film
formed on the surface of the permanent magnet. Alternatively, the
resin film may be formed on the surface of the metal film formed on
the surface of the permanent magnet. In addition, the chemical
adsorption film may be formed on the surface of such resin film.
The use of a plurality of different films combined offers
synergetic effect to further enhance the corrosion resistance of
the permanent magnet.
[0047] The permanent magnet may be a rare-earth magnet. From the
viewpoint of magnetic properties, the rare-earth magnet is more
suitable than the ferrite magnet for use as the permanent magnet of
the motor-driven compressor. On the other hand, however, the
rare-earth magnet is more prone to corrode than the ferrite magnet.
Therefore, the use of the motor-driven compressor having the
protective film on the surface of the permanent magnet for
improving the corrosion resistance of the permanent magnet and
having the gap between the permanent magnet and a wall of the
magnet hole filled with a fixing resin for fixing the permanent
magnet to the wall of the magnet hole, is particularly effective
for this case.
[0048] The motor-driven compressor is preferably used for a
vehicle-mounted air conditioner having a refrigerant circulation
path in which a nonmetallic duct is connected. The vehicle-mounted
air conditioner includes a condenser, an expansion valve and an
evaporator as well as the compressor that are connected by the
refrigerant circulation path. The refrigerant circulation path is
sealingly filled with refrigerant and lubricating oil. Nonmetallic
duct such as resin duct may be used in part of the duct forming the
refrigerant circulation path to impart the flexibility to the duct
and to enhance the vibration-damping property. The term "resin" is
used herein in a broad sense, including natural resin, synthetic
resin, natural rubber and synthetic rubber. The nonmetallic duct
such as resin duct is more prone to permit water permeation. If the
nonmetallic duct is used for a long period of time in hot and humid
conditions, water in the air may enter the refrigerant circulation
path via the nonmetallic duct such as resin duct. Due to the
ingress of water into the refrigerant circulation path, refrigerant
and/or lubricating oil may change their properties thereby to
produce acid. Therefore, the use of the motor-driven compressor
having the protective film on the surface of the permanent magnet
for improving the corrosion resistance of the permanent magnet and
having the gap between the permanent magnet and a wall of the
magnet hole filled with a fixing resin for fixing the permanent
magnet to the wall of the magnet hole, is particularly effective
for the vehicle-mounted air conditioner.
[0049] The motor-driven compressor is preferably used in a
refrigeration system through which the refrigerant that is
expressed by molecular formula of C.sub.3H.sub.mF.sub.n having one
double bond in a molecular structure of the molecular formula,
where m is an integral number of 1 to 5, n is an integral number of
1 to 5, and m+n=6, or a mixed refrigerant containing such
refrigerant circulates. There is a general trend that a refrigerant
having less impact on the ozone layer than the refrigerant that has
been referred to generally as chlorofluorocarbon has been used
preferentially as the refrigerant for the refrigeration system. As
such a new type of refrigerant, the refrigerant that is expressed
by molecular formula of C.sub.3H.sub.mF.sub.n having one double
bond in a molecular structure of the molecular formula, where m is
an integral number of 1 to 5, n is an integral number of 1 to 5,
and m+n=6, such as 2,3,3,3-tetrafluoro-1-propene
(CF.sub.3--CF.dbd.CH.sub.2), has been attracting the attention from
the industry. Such refrigerant is referred to as HFO1234yf type
refrigerant.
[0050] The HFO1234yf type refrigerant is relatively prone to
dissolve in the presence of water because it contains the double
bond. If water is mixed with refrigerant in the refrigerant
circulation path for any reason during the manufacturing process of
the compressor or during the market use, the refrigerant may
dissolve thereby to produce hydrofluoric acid (HF). Acid such as
hydrofluoric acid causes the permanent magnet to corrode relatively
early. Therefore, the use of the motor-driven compressor having the
protective film on the surface of the permanent magnet for
improving the corrosion resistance of the permanent magnet and
having the gap between the permanent magnet and a wall of the
magnet hole filled with a fixing resin for fixing the permanent
magnet to the wall of the magnet hole, is particularly effective
for the refrigeration system using the HFO1234yf type
refrigerant.
[0051] The motor-driven compressor is effective when the housing
has therein lubricating oil containing at least one of polyolester
(POE), polyvinyl ether (PVE) and polyalkylene glycol (PAG). The
ingress of water or acid into the refrigerant circulation path is
undesirable also in the case where the motor-driven compressor
contains such lubricating oil in the housing. For example,
polyolester hydrolyzes in the presence of water thereby to produce
organic carboxylic acid. As in the case of the hydrofluoric acid,
the organic carboxylic acid may cause the permanent magnet to
corrode. Therefore, the use of the motor-driven compressor having
the protective film on the surface of the permanent magnet for
improving the corrosion resistance of the permanent magnet and
having the gap between the permanent magnet and a wall of the
magnet hole filled with a fixing resin for fixing the permanent
magnet to the wall of the magnet hole, is particularly effective
for this case.
[0052] It is preferred that the rotor has a rotor body and a pair
of end plates, that the magnet hole of the rotor extends through
the rotor body in an axial direction of the rotor body, and that
the paired end plates are disposed at opposite ends in the axial
direction of the rotor body for closing the magnet hole. In this
case, the paired end plates close the magnet hole thereby reducing
the chance of the permanent magnet contacting with the refrigerant
containing water causing the deterioration of the permanent magnet,
which reduces the deterioration of the permanent magnet.
[0053] In a case where the rotor body is formed of a plurality of
magnetic steel plates laminated together, on the other hand, it is
difficult to completely prevent the refrigerant from entering the
magnet hole via slight gap between the laminated magnetic steel
plates. In the motor-driven compressor of the present invention,
therefore, it is preferred that an entire outer surface of the
rotor is coated with a resin film. The resin film prevents the
ingress of water or acid into the magnet hole.
[0054] The term "resin" as in the resin film is used herein in a
broad sense, including natural resin, synthetic resin, natural
rubber and synthetic rubber. The resin forming the film includes
resin or rubber of, for example, polyethylene series, epoxy series,
fluorine series, acrylic series, polyamide series, polyamide-imide
series, silicone series, polyether ether ketone (PEEK) series,
polyetherimide series, phenolic series, melamine series and
urethane series. Of these resins, fluorine series resin is suitable
for use because of its high flexibility.
[0055] In the motor-driven compressor of the present invention, the
electric motors may be of either of a first type wherein the rotor
rotating with the rotary shaft is disposed radially inward of a
cylindrical stator or a second type wherein a cylindrical rotor is
disposed radially outward of the stator. In the first type of
electric motor, the permanent magnet is formed of a flat plate and
a plurality of the permanent magnets is disposed so as to form a
polygon in cross section perpendicular to the axial direction of
the rotor. In the second type of electric motor, the permanent
magnet is formed of a curved plate whose cross section is arched
and a plurality of the permanent magnets is disposed so as to form
a circle in cross section perpendicular to the axial direction of
the rotor.
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