Electric compressor

Details Electric compressor Electric compressor

2001-06-15

2003-04-15

Walberg, Teresa (Department: 3742)

Pumps

Motor driven

Electric or magnetic motor

C417S902000

Reexamination Certificate

active

06547538

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an electric compressor used in a freezer, refrigerator, or air-conditioner. More particularly it relates to a highly efficient electric compressor in which loss torque and iron loss due to magnetic attraction are reduced. The magnetic attraction is produced at a bearing in a compressing section jointed to a motor section of the compressor.
BACKGROUND ART
A prior art is described with reference to
FIG. 7
where a reciprocal electric compressor is shown.
In
FIG. 7
, the compressor comprises hermetic container
1
, compressing section
2
disposed at lower part of the container, and motor section
3
disposed above the compressing section. Shaft
4
mounted to rotor
14
of motor section
3
has crank
4
a
on its tip.
Cylinder block
5
formed of a casting made of iron system material comprises bearing
6
, in which shaft
4
is inserted, and cylinder
7
formed at right angles with bearing
6
.
Piston
9
is linked to crank
4
a
via connecting rod
8
. When motor section
3
is driven, rotating movement of shaft
4
is converted to reciprocal movement by crank
4
a
, and delivered to piston
9
via rod
8
, so that piston
9
slides with respect to inner wall of cylinder
7
. Compressing chamber
10
is formed by cylinder
7
and piston
9
. Oil pipe
11
is mounted to a tip of crank
4
a
, and lubricant
12
pooled at the bottom of hermetic container
1
is lubricated to compressing section
2
and shaft
4
through oil pipe
11
, so that respective sliding sections move smoothly.
Motor
3
is a two-pole induction motor comprising the following elements: (a) stator
13
formed of winding-wound-iron-core made of laminated magnetic sheets, and (b) rotor
14
formed of rotor iron core
15
with a secondary conductor, the rotor iron core being made of laminated magnetic sheets.
Bored section
16
is provided at the end of rotor-iron-core
15
on the side of compressing section
2
, and bearing
6
extends inside bored section
16
.
An operation of the conventional reciprocal compressor of which structure is discussed above is described hereinafter.
When rotor
14
spins, piston
9
performs reciprocal movement via connecting rod
8
linked to crank
4
a
of shaft
4
, so that piston
9
compresses coolant gas in compressing chamber
10
. The compressed gas is discharged through a discharging pipe (not shown) to a system such as a freezer, refrigerator, or air-conditioner.
Regarding the lubrication to respective sliding sections such as bearing
6
, cylinder
7
, connecting rod
8
and piston
9
of compressing section
2
, oil pipe
11
mounted to lower end of shaft
4
rotates and pumps up lubricant
12
for lubrication.
Recently, reducing the power consumption of freezers, refrigerators, and air-conditioners has drawn attention because of energy saving tendency, and lower profiles of those apparatuses have been studied because of downsizing requirement. The rotor is disposed as close as possible to the compressing section, and a part of bearing extends inside the bored section, thereby regulating undesirable rotating deflection of the rotor and lowering the total height of the compressor. Thus the downsizing requirement is satisfied. However, power saving of the motor, which consumes the largest power in the freezing system, has not yet arrived at a satisfactory level.
In the conventional two-pole induction motor used in compressors, magnetic steel sheets of lower iron loss has been employed, a shape of the core has been optimized, or volume of materials used has been increased, in order to raise the efficiency of the motor. The induction motor, however, needs the exciting power for forming a magnetic circuit in addition to the power for producing torque as well as rotating load. Accordingly, efficiency improvement of the motor tends to be saturated, and it is difficult to expect a further substantial improvement of the efficiency.
A self-starting-synchronous-type two-pole motor using permanent magnets draws attention as another measures for increasing the efficiency of the motor. Because the permanent magnets are buried in the rotor, thereby eliminating the exciting power.
An example of this self-starting-synchronous-motor is described with reference to
FIGS. 8 and 9
. Regarding the entire compressor, only the motor is changed, and the changed points are detailed hereinafter.
Rotor
17
of the synchronous motor comprises iron core
18
made of laminated magnetic steel sheets and shaft hole
19
for receiving shaft
4
to fit into core
18
. Bored section
20
is provided at the end of core
18
in an axial direction. It is not shown in the drawings, but a part of bearing
6
of a cylinder block
5
extends inside bored section
20
.
Two pieces of plate-type permanent magnet
21
butt each other and form angle a to shape in a hill. Two pairs of these magnets
21
are inserted into rotor
17
. A first pair of two magnets are placed such that S pole faces outside the rotor and N pole faces inside the rotor. A second pair of two magnets are placed such that N pole faces outside the rotor and S pole faces inside the rotor. Thus the first pair forms a rotor pole and the second pair forms another pole, so that entire rotor
17
has two poles. The width of magnet
21
is referred to as “P”.
A starter cage-shaped conductor is unitarily formed by aluminum diecasting comprising numbers of conductive bars
22
provided to core
18
and shorting grommets
23
covering both ends of core
18
in an axial direction.
Both end-faces of core
18
in the axial direction have protective terminal plates
24
made of non-magnetic material for securing magnets
21
from coming off. Barriers
25
, for preventing magnetic flux between the permanent magnets from shorting, are provided to core
18
. Barriers
25
are unitarily formed with the starter cage-shaped conductor by the aluminum diecasting.
The flow of magnetic flux from magnet
21
is schematically described with reference to
FIG. 9
using the arrow marked lines. The magnetic flux from N poles of two magnets
21
placed at upper side of
FIG. 9
travels mainly through the center section of core
18
and is attracted to S poles of two magnets
21
placed at lower side of FIG.
9
. Thus the magnetic density through core section
18
a
around the outer rim
20
a
of bored section becomes substantially high.
As such, self-starting-synchronous type motor using permanent magnets can be used instead of the conventional induction motor. However, since bearing
6
made of iron-system material exists inside bored section
20
, magnetic attraction works between the inner wall of bored section excited and the outer wall of bearing
6
. The magnetic attraction produces loss torque which lowers the torque produced by the motor, and yet, magnetic flux of magnet
21
travels to bearing
6
and produces eddy-current-loss. The motor needs another power to compensate the loss torque and eddy-current-loss in order to continue operating, and this prevents the efficiency from increasing.
DISCLOSURE OF THE INVENTION
The present invention addresses the problem discussed above, and aims to provide a highly efficient electric compressor in which loss torque due to magnetic attraction and iron loss (particularly eddy-current-loss) in the bearing are reduced.
The compressor of the present invention comprises the following elements:
a compressing section accommodated in a hermetic container; and
a motor section for driving the compressing section and coupled to the compressing section.
The motor section includes a motor of two rotor poles, and the motor has a bored section at an end on the compressing section side and a rotor core in which permanent magnets are buried. The compressing section includes a bearing, made of non-magnetic material, extending inside the bored section.
This structure allows magnetic attraction not to work between an inner wall of the bored section and an outer wall of the bearing, so that no loss torque is produced. Since the bearing is made of non-magnetic material, magnetic flux from the perm

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