Electrical generator or motor structure – Dynamoelectric – Linear
Reexamination Certificate
1999-02-05
2001-02-06
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Linear
C310S023000
Reexamination Certificate
active
06184597
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a movable magnet type linear motor and further to a linear compressor.
2. Description of the Related Art
In recent years, linear motors have been in active development. Heretofore, in Europe and America, a linear motor has been studied for use in a Stirling engine to be used in the outer space. In the late years, the American SUNPOWER Co., Ltd. has developed a linear compressor and a movable magnet linear motor for a compressor to be used under common environments (Nicholas R. van der Walt, Reuven Unger: Linear Compressors-amturing technology, International Appliance Technical Conference, pp1-6, 1994).
FIG. 37
is a schematic illustration of a conventional linear motor.
The linear motor, generally designated at numeral
300
, is made up of a cylindrical inner yoke
301
, an outer yoke
304
including two magnetic pole portions
302
,
303
, a coil
306
wound around a central axis
305
and a moving element
308
having a cylindrical permanent magnet
307
.
In this configuration, on supply of an alternating current to the coil
306
, different magnetic poles alternately take place axially in the magnetic pole portions
302
,
303
, and the magnetic attraction and repulsive action with the permanent magnet
307
of the moving element
308
generate a thrust proportional to the magnitude of the current in the coil
306
and the magnetic flux density in the permanent magnet
307
, so that the moving element
308
reciprocates in synchronism with the frequency of the alternating current.
In the aforesaid conventional example, the inner yoke
301
and the outer yoke
304
are constructed in a manner that a large number of sheets (thin plates) each having a high magnetic permeability are piled up each other. The eddy current loss of the motor shows a property proportional to the square of the plate thickness of the yoke material, and therefore, such a configuration as seen in the conventional example is capable of reducing the eddy current loss to improve the lowering of the motor efficiency due to the core (iron) loss, as compared with the case that the yoke is merely formed with a metallic block.
There is a problem which arises with the configuration of the conventional linear motor, however, in that, since the yoke has a cylindrical shape to make a dimensional difference between its inner circumferential section and its outer circumferential section, considerable difficulty is encountered in accurately piling up sheets having an even thickness toward its central axis at the fabrication. For this reason, the sheets have been made not to have an even thickness, but the outer circumferential section has been designed to have a slightly greater thickness to form it into a wedge-like shape. However, this contributes to an extremely high manufacturing cost.
Furthermore,
FIG. 38
is a cross-sectional view showing a construction of a conventional linear compressor. In
FIG. 38
, a linear compressor, designated at numeral
400
, is composed of a cylinder
401
, a piston
402
inserted into the cylinder
401
to be allowed to reciprocate therein, a compression chamber
403
defined in a state of facing a head of the piston
402
, and a suction (inlet) valve (not shown) and delivery (outlet) valve (not shown) openable and closable in response to a gas pressure in the compression chamber
403
.
The linear compressor
400
is additionally equipped with a linear motor
406
for making the piston
402
reciprocate and a resonance spring
407
for supporting the piston
402
to allow the reciprocation of the piston
402
. The linear motor
406
comprises a cylindrical inner yoke
408
, an outer yoke
411
including two magnetic pole portions
409
,
410
, a coil
413
and a moving element
415
having a cylindrical permanent magnet
414
, with the moving element
415
being in connection with the piston
402
.
On supply of an alternating current to the coil
413
, different magnetic poles alternately take place axially in the magnetic pole portions
409
,
410
, the magnetic attraction and repulsive action with the permanent magnet
414
of the moving element
415
develops a thrust proportional to the magnitude of the current in the coil
413
and the magnetic flux density of the permanent magnet
414
, so that the moving element
415
reciprocates in synchronism with the frequency of the alternating current, and consequently, the piston
402
also reciprocates. Further, when the interior of the compression chamber
403
assumes a low pressure condition, an expanded gas is taken through the suction valve into the compression chamber
403
, while, when assuming a high pressure condition, a compressed gas is discharged from the compression chamber
403
through the delivery valve, thus serving as a compressor.
The core (iron) loss such as an eddy current loss and a hysteresis loss hinders the improvement of a motor and a compressor. Since the eddy current loss is proportional to the square of the thickness of the yoke material, it is effective that a yoke is constructed by piling up sheets. However, as mentioned above, the conventional linear motor or the linear motor of the conventional linear compressor is composed of a yoke having a cylindrical configuration, and this cylindrically configured yoke encounters considerable difficulty in accurately piling up sheets toward its central axis at its fabrication.
SUMMARY OF THE INVENTION
The present invention has been developed with a view to eliminating these problems, and it is therefore an object of this invention to provide a linear motor which is capable of lessening the eddy current loss to improve the motor efficiency and of facilitating the manufacturing of the yoke at a lower cost.
Another object of this invention is to provide a linear compressor which is capable of improving the compressor efficiency and of facilitating its manufacturing.
For solving these problems, in accordance with this invention, there is provided a linear motor comprising a central axis, prismatic inner yokes each constructed in a manner that a number of sheets each having a generally rectangular configuration and having a high magnetic permeability are piled up each other, and outer yokes each constructed in a manner that a number of sheets each having a generally rectangular configuration and having a high magnetic permeability are likewise piled up each other, with each of coils being wound around a central portion of three magnetic pole portions of the outer yoke to alternately and axially establish different magnetic poles, wherein a surface of the outer yoke, which has the three magnetic pole portions, is disposed in an opposed relation to the corresponding inner yoke to define a predetermined gap therebetween so that the inner yoke and the outer yoke form each of a plurality of yoke blocks, and the plurality of yoke blocks are placed around the central axis to form a polygonal configuration so that the sheet piling-up direction is perpendicular (orthogonal) to a diametrical direction of a shaft including the central axis, and a moving element having a pair of flat-plate-like permanent magnets magnetized radially so that their magnetizing directions are opposite to each other and located between the inner yoke and the outer yoke in a state of being arranged at a predetermined interval along a direction of the central axis is placed to be movable along a direction of the central axis.
This permits the reduction of the core loss leading to the improvement of the motor efficiency and facilitation of the fabrication of the linear motor.
Furthermore, in accordance with this invention, there is provided a linear motor comprising: prismatic inner yokes each formed by piling up a number of sheets each having a generally rectangular configuration and having a high magnetic permeability; outer yokes each formed by piling up a number of sheets
4
each having a generally rectangular configuration and having a high magnetic permeability, each of the outer yokes having first and second sl
Hamaoka Koji
Shibuya Koyo
Yamamoto Hideo
Dougherty Thomas M.
Gopstein Israel
Jones Judson H.
Matsushita Refrigeration Company
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