Pumps – Condition responsive control of pump drive motor – By control of electric or magnetic drive motor
Reexamination Certificate
1998-03-06
2001-05-15
Solis, Erick (Department: 3747)
Pumps
Condition responsive control of pump drive motor
By control of electric or magnetic drive motor
C417S417000, C417S534000
Reexamination Certificate
active
06231310
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a linear compressor which compresses and externally supplies gas by driving a piston fit within a cylinder to move back and forth by a linear motor.
BACKGROUND OF THE INVENTION
In recent years, there have been developed linear compressors as a mechanism for compressing and supplying refrigerant gas in a refrigeration system. As shown in
FIG. 26
, for example, a linear compressor includes a cylindrical housing
101
having a bottom, a magnetic frame
102
of a low carbon steel formed at the upper end opening of housing
101
, a cylinder
103
formed in the central portion of magnetic frame
102
, a piston
105
fit within cylinder
103
, capable of moving back and forth and defining a compression chamber
104
in the space of cylinder
103
, and a linear motor
106
serving as a driving source to drive piston
105
to reciprocate.
Linear motor
106
has an annular permanent magnet
107
provided at an outer concentric position with cylinder
103
and fixed to housing
101
. A magnetic circuit formed of magnet
107
and magnetic frame
102
produces a magnetic field B in a cylindrical gap
108
concentric with the center of cylinder
103
. A cylindrical mobile body
109
having a bottom, formed of resin and integrally fixed to piston
105
is provided in gap
108
in the center, and a coil spring
110
for elastically supporting mobile body
109
and piston
105
and permitting them to reciprocate is fixed to housing
101
.
An electromagnetic coil
111
is wound around the outer circumference of mobile body
109
at a position opposite to magnet
107
, ac current at a prescribed frequency is passed through a lead (not shown) to drive coil
111
and mobile body
109
by the function of a magnetic field through gap
108
to force piston
105
to move back and forth within cylinder
103
, and gas pressure is generated at a prescribed cycle in compression chamber
104
.
Meanwhile, as shown in
FIG. 27
, there is known, as a representative refrigerating system, a closed type refrigerating system in which a linear compressor
121
(compressor), a condenser
122
, an expansion valve
123
and an evaporator
124
are connected by a gas flow path pipe
125
. Linear compressor
121
is used as a device to compress to a high pressure a refrigerant gas evaporated at evaporator
124
and taken in through gas flow path pipe
125
, and let out, thus pressurized, to condenser
122
through gas flow path pipe
125
.
Therefore, as shown in
FIG. 26
, compression chamber
104
is connected with gas flow path pipe
125
outside housing
101
through a valve mechanism
112
provided at the upper end portion of cylinder
103
. Valve mechanism
112
includes an inlet valve
112
a
which permits only refrigerant gas from evaporator
124
to enter through gas flow path pipe
125
, and an outlet valve
112
b
which permits only refrigerant gas to be let out to condenser
122
through gas flow path pipe
125
. Inlet valve
112
a
allows gas to flow toward compression chamber
104
by the difference in pressure of refrigerant gas between gas flow path pipe
125
on the low pressure side and compression chamber
104
.
Outlet valve
112
b
allows gas to flow toward gas flow path pipe
125
on the high pressure side by the difference in pressure of refrigerant gas between compression chamber
104
and gas flow path pipe
125
on the high pressure side. Note that inlet valve
112
a
and outlet valve
112
b
are both energized by a plate spring.
Thus, in the conventional device, refrigerant gas taken in from inlet valve
112
a
is compressed to a high pressure in compression chamber
104
, and supplied to condenser
122
through outlet valve
112
b.
In addition, in recent years, as disclosed by Japanese Patent Laying-Open No. 2-154950, for example, there has been proposed a technique of improving the efficiency by providing compression chambers on both sides in a housing and alternately operating two pistons by a single linear motor.
The linear compressors are divided into two kinds, in other words, those like a coil mobile linear compressor as disclosed by Japanese Patent Application No. 8-179492, and those like a magnet mobile type linear compressor as disclosed by Japanese Patent Application No. 8-108908. These two kinds of linear compressors both produce compressed gas in a compression chamber by driving a piston to move back and forth using a driving force obtained from a linear motor.
The above-described linear compressors are, however, encountered with various problems as follows.
First Problem
The conventional single piston type linear compressor is largely affected by non-linear force produced within a compression chamber associated with inputting-king/compression/exhaustion of a gas, and the thrust of the motor cannot be linearized, which makes it difficult to improve the efficiency.
Furthermore, the neutral point of the piston fluctuates with the fluctuation of load at the time of activation for example, and the stroke of the piston cannot be readily controlled.
Second Problem
In a conventional linear compressor
121
, piston
105
is driven by linear motor
106
to move up and down within cylinder
103
, and mobile body
109
also moves up and down, which causes gas present in the space in the magnetic circuit formed by magnetic frame
102
, permanent magnet
107
and mobile body
109
, and gas present in the space inside the mobile body on the back side of piston
105
surrounded by the inner surface portion of mobile body
109
to perform compression/expansion work as mobile body
109
moves up and down, which could lead to irreversible compression losses in linear compressor
121
.
As a countermeasure, gap
108
may be sufficiently secured to provide a sufficient gap between magnetic frame
102
and mobile body
109
and between permanent magnet
107
and electromagnetic coil
111
, but the thrust of linear motor
106
decreases in this case, which lowers the operation efficiency of linear compressor
121
.
Third Problem
In linear compressor
121
as described above, piston
105
is driven by linear motor
106
to move up and down within, and slidably in contact with, cylinder
103
, and a kind of slide bearing is formed between the piston and the cylinder.
In the conventional structure as described above, however, a force (radial force) in the direction vertical to the moving direction of the piston is generated because of the problem of processing precision and a distortion in the electromagnetic force of the electromagnetic coil, and if the radial force is large, the operation efficiency may be lowered because of frictional losses, the life of the device may be shortened because of abrasion at a gas seal portion provided at piston
105
, and the refrigerant may be contaminated by dust created by abrasion.
Fourth Problem
The linear compressor disclosed by Japanese Patent Laying-Open No. 2-154950 employs a magnet mobile type linear motor driving method rather than the coil mobile type as described above and shown in
FIG. 26
, force by magnetic field in the direction vertical to the moving direction of the piston is applied to the piston, the piston portion is prone to abrasion and therefore the compressor is not suitable for such use.
Therefore, in a linear compressor to be used for a long period of time, the driving method of the linear motor may be changed to the coil mobile type, according to which force by the magnetic field of the linear motor acts only in the same direction as the mobile direction of the piston.
Furthermore, gas present in the back space of the piston performs compression/expansion work as the piston moves back and forth, which could lead to irreversible compression losses in linear compressor
121
.
In addition, in the conventional linear compressor, the central position of the stroke of piston cannot be controlled at a prescribed position, and therefore highly efficient operation cannot be performed.
Fifth Problem
In the refrigerating system as described above, compressed gas obtained in the compression chamber
Kuwaki Yasuyuki
Matsumura Shinichi
Nakayama Takafumi
Takaoka Taizo
Tojo Naoto
Armstrong, Westerman Hattori, McLeland & Naughton
Sanyo Electric Co,. Ltd.
Solis Erick
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