Note: Descriptions are shown in the official language in which they were submitted.
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ELECTROMAGNETICALLYACTUATED RECIPROCATING
COMPRESSOR DRIVER
FIELD OF THE INVENTION
The present invention relates generally to a driver for an
5 electromagnetically actuated valve, and more particularly to an electromagnetically
actuated compressor driver which creates linear reciprocating motion directly.
BACKGROUND OF THE INVENTION
One basic problem with a standard refrigerator compressor is the
inefficiency of the compressor due to the friction generated by the piston drive10 mechanism in the standard compressor. A standard reciprocating refrigerator
compressor uses a motor to rotate a crankshaft, which in turn moves a piston up
and down within a compression chamber. Referring to FIG. 1, a typical refrigerator
compressor 10 is shown. More specifically, the induction motor 12 creates a
torque on the crankshaft 14 which causes the piston 16 to move back and forth
15 within the cylinder 18 via a connecting rod 20. During operation, the force
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exerted by the compressing gas is transferred through the
piston's spherical bearing 22 down the connecting rod 20 to the
connecting rod bearing 24 and and finally to the crankshaft
bearings 26. These bearings are all heavily side loaded, creating
5 a great amount of friction. As a result, the bearings must be
continuously lubricated to prevent the heat build-up which will
eventually burn out the bearing.
Therefore, a need exists for a compressor driver that
o provides the required piston movement without producing
undesired amounts of friction.
Another problem with the standard compressor is that its
manufacturing process is complex, and therefore relatively
15 expensive. The conventional induction motor in the compressor is
constructed from a laminated stack of silicon-iron sheets, with a
copper coil complexly woven throughout. The motor's stator is
assembled by stamping appropriately-shaped individual laminates
from a coiled sheet silica-iron. Typically over one hundred
20 individual laminates are required. The laminates are varnished,
stacked in a jig, and welded along the side to create one integral
unit. Coil slots and holes are machined into the stacked
assembly, and plastic insulation inserts are placed in the slots
and holes. Copper wire is then woven into the inserts by a
25 complex coil winding machine. The coil extensions are then
machine stitched, the entire assembly vacuum impregnated with
epoxy, and baked. Similarly, the conventional compressor's rotor
assembly requires stacked laminates, wherein the number of
laminates and the process of stacking is identical to that
30 required for the stator.
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The standard compressor further requires three precision
bushings and and a complex spherical bearing. These parts
require precision grinding and hardened materials to provide the
requisite durability. Therefore, the manufacturing process of the
5 conventional compressor requires extensive equipment and
processing, and is therefore a costly process. In comparison, in
the compressor of the present invention, the manufacturing
process is simple, does not require the above-discussed complex
manufacturing process, and only requires precision grinding for
o the piston and cylinder. Furthermore, the compressor of the
present invention uses considerably less copper wire than the
typical compressor, and therefore is less expensive in material
costs .
Therefore, a need also exists for a compressor that is
inexpensive and relatively simple to manufacture.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention
to overcome one or more disadvantages and limitations of the
prior art.
A significant object of the present invention is to provide
2s an electromagnetic compressor valve that operates at a higher
efficiency than the prior art compressor valves.
Another object of the present invention is to provide an
electromagnetic compressor driver that creates linear piston
motion directly.
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Another object of the present invention is to provide an
electromagnetic compressor driver that eliminates the need for
dynamic seals.
Still another object of the present invention is to provide
an electromagnetic compressor driver that operates with reduced
friction, reduced wear and at a reduced operating temperature
than the prior art compressor drivers.
o Another object of the present invention is to provide an
electromagnetic compressor driver that operates with reduced
vibration and noise than the prior art compressor drivers.
It is yet another object of the present invention to provide a
compressor that is inexpensive and relatively simple to
manufacture.
According to a broad aspect of the present invention, a
compressor includes an electromagnetic actuator for driving the
piston in the compression cylinder. The actuator includes an
electromagnetic element having a core and a coil. The core has
an electromagnet surface and a channel extending through the
core. The coil is disposed in the channel. An axially
reciprocating armature element is interconnected with the
piston. The armature element defining an axial stroke having a
stroke midpoint and a stroke peak. The armature element also has
an armature surface dimensioned to align with and correspond to
the electromagnet surface at the stroke peak. The actuator also
includes a primary spring disposed on one end of the armature
element for biasing the armature from movement in an axial
direction. A secondary spring is disposed on the opposing end of
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the armature element and biases the armature from movement in
an opposite axial direction. The armature is biased by the springs
to resonate at a pre-determined frequency. Applying current to
the coil in the electromagnetic element when the armature
5 surface passes through the stroke midpoint allows the armature
surface to overcome losses due to friction and compression
forces, and causes the armature surface to continue resonating at
the predetermined frequency.
o A feature of the present invention is that the
electromagnetically actuated valve directly produces linear
piston movement in the compressor.
Yet another feature of the present invention is that amount
S of friction produced by the piston movement in the compressor is
greatly reduced from the prior art by the use of the
electromagnetically actuated driver due to the elimination of
side-loaded bearings.
These and other objects, advantages and features of the
present invention will become readily apparent to those skilled in
the art from a study of the following description of an exemplary
preferred embodiment when read in conjunction with the attached
drawing and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional view of a prior art
30 refrigerator compressor valve; and
WO 94/18681 213 3 ~ 9 ~ PCT/US94/01123
Figure 2 is a cross-sectional view of one embodiment of
the compressor valve of the present invention.
Figure 3 is an alternative embodiment of the compressor
s valve and driver of the present invention.
DESCRIPTION OF AN EXEMPLARY PREFERRED EMBODll\llENT
o Referring now to Figure 2, one embodiment of a compressor
50 with an electromagnetically actuated valve driver 52 is shown
in cross-section. In the embodiment shown, the compressor S0
includes a compressor containment can 54, a compression
cylinder 56, a piston 58, and the electromagnetically actuated
S driver 52 for controlling the movement of the piston 58 in the
compressor 50.
The containment can 54 includes a low pressure intake port
60,a high pressure outlet port 62, and, which is connected to a
reed valve 98. The cylinder 56 is disposed within the
containment can 54, and includes a cylinder cover 64. The
compressor is located between an upper support surface 66 and a
lower support surface 68. The upper support surface 66 defines a
preferably cylindrical aperture 70, providing a location for the
cylinder 56, within which the piston 58 is disposed. The aperture
70 also defines an aperture upper end 72 and an aperture lower
end 74, which defines the top and bottom of the cylinder. The
electromagnetically actuated valve driver controls the movement
of the piston 58 between the upper end 72 and the lower end 74 of
the aperture 70.
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The electromagnetically actuated valve driver 52 includes an
electromagnetic element 76, including a core element 77 and a coil 80, an
armature element 78, a retaining bar 82, a valve shaft 96, a support spring 84, and
at least one lower spring 86. The core 77 of the electromagnetic element 76 has
a first face 104, with an opening at the first face 104 that extends through thecore element to define a central chamber 88. The electromagnetic element 76
preferably has annular horizontal cross-section. The first face 104 of the core
element 77 further includes a central channel 90 that extends around the centralchamber 88.
In an alternative embodiment of the invention, the electromagnetic
element 76 may be toroidal-shaped, and extend annularly around the valve shaft
96, or have a substantially U-shaped vertical cross-sectional area. The
electromagnetic element 76 therefore defines two open polar faces 92 which
provide a large electromagnetic pole face area. This alternative configuration is
explained in detail in co-owned U.S. Patent No. 5,222,714 of June 29, 1993.
Referring still to FIG.2, in the embodiment shown, the central channel
90 has a top portion 106 preferably of a frustoconical cross-section, and a bottom
portion 108. The frustoconical top portion defines two polar faces 92 of the
electromagnetic element 76 extending from the channel 90, each of the polar faces
20 extending at a pre-selected angle. The armature element 78 also preferably has an
annular horizontal cross-section. The armature 78 has a raised portion 110 that
is dimensioned to fit in the top portion 106 of the channel 90. The armature raised
portion defines two armature pole faces 94, which are at an armature pole face
angle corresponding to the pre-selected electromagnet angle. The armature pole
25 faces 94 are angled for maximum contact with the electromagnetic element 76.
The angle of the pole faces relative to the stroke motion of the valve serves tominimize the amount of electromagnetic energy required to pull the valve from anopen to closed position and compress the gap. The angle of the electromagnetic
pole faces 92 and armature pole faces 94 are also selected so as to provide a polar
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surface that provides adequate electromagnetic force to match the force that is
exerted by compressing gas on the piston during the compression cycle. The
process of calculating the required values for the angles of the polar faces andother dimensions is explained in detail in co-owned U.S. Patent No. 5,222,714.
5 More specifically, the shape of the electromagnetic face 92 and aperture face 94
define the electromagnets force to gap relationship. As the angle of the
electromagnetic face in relation to the horizontal axis increases, the wider the gap
is through which the aperture face can be attracted to the electromagnet. For a
compressor application, the face is shaped such that the force applied by the
10 electromagnet matches closely to the force exerted by the gas compressing onto
the piston.
The coil 80 extends within the bottom portion 108 of the central
channel of the electromagnetic element and is bonded to the electromagnetic
element. The central location of the coil element and the cross-sectional shape of
1 5 the electromagnetic element provides maximized magnetomotive force with minimal
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resistance. The valve shaft 96 is disposed within the central
~ chamber 88 of the electromagnetic element 76. The piston 58 is
connected to one end of said shaft 96. The retaining bar 82
connects the armature element 78 to the valve shaft 96.
s Therefore, the piston 58, valve shaft 96, and armature element 78
combine to form a moving assembly.
The support spring 84 is disposed within the central
chamber 88 of the electromagnetic element 76 and extends from
~o the retaining bar 82 to the upper support 66. Therefore, the
support spring 84 restrains the armature 78 from upper
movement. In the embodiment shown, two lower springs 86
extend from the armature element 78 or retaining bar 82 to the
lower support surface 68 of the cylinder 56. The lower springs
5 restrain the armature 78 from downward movement.
Referring still to FIG. 2, the operation of the compressor 50
will be described. The support spring 84 and lower springs 86
bias the armature in its initial spaced apart position from the
20 electromagnetic element. In order to and raise the piston 58 to
the upper end 72 of the aperture 70, the electromagnet 76 is
energized by applying current to the coil 80, creating an
electromagnetic field. The electromagnetic field attracts the
armature 78 towards the electromagnet 76. Because the
25 armature 78 is attached to the piston 58 via the retaining bar 82
and shaft 96, the movement of the armature 78 towards the
electromagnet 76 moves the piston 58 in the aperture 70 toward
the aperture upper end 72. The upward movement of the armature
78 also causes the compression of the support spring 84, thereby
30 storing energy in the support spring 84.
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When the moving assembly, consisting of the piston, shaft,
and armature reaches the uppermost position in the aperture 70,
the current in the coil 80 is interrupted, and the moving assembly
is forced downward by the compressed support spring 84. The
5 momentum of the moving assembly causes it to drive past its
center position, compressing the lower spring 86. The lower
springs 86 therefore slows and eventually stops the downward
movement of the moving assembly. As the piston is moving
downward, refrigeration gas is drawn into the compression
o chamber through the intake valve 60 and reed valve assembly 98.
After the lower springs 86 stop the downward movement of
the moving assembly, the compressed lower springs 86 drive the
moving assembiy upward, past its center point and toward the top
S of its stroke. As the piston 58 moves upward in the aperture 70
the pressure increase in the compression chamber causes the
intake valve to close, and the compression of the gas begins. As
the piston begins to move from its bottom position, the amount of
force required to compress the gas is low. However, as the piston
20 moves upward in the compression cylinder, the amount of force
required increases, and it therefore becomes necessary to apply
an external force in order to drive the piston to its uppermost
position. The external force is applied by energizing the
electromagnet 76, as described above. The size and shape of the
25 electromagnet is designed such that the amount of
electromagnetic force generated matches the restricting force
generated by the compressed gas, so as to allow the piston to
reach its uppermost position. Once the piston reaches its
uppermost position, the current to the coil element is
30 interrupted, the moving assernbly is driven downward by the
compressed support spring 84. and the cycle is repeated.
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An addition feature of the present invention is the vibration
cancellation system of the compressor. As shown in FIG. 2, the
compressor includes two upper springs 100 and a spring mounted
5 reaction mass 102. The compression and extension of the support
spring 84 drives the reaction mass 102 180 degrees out-of phase
with the moving assembly. The matching of the weight of the
reaction mass 102 to the weight of the moving assembly causes
the natural and nearly complete cancellation of rectilinear
o vibrations. Any remaining small amounts of vibration eliminated
by mounting the compressor assembly to springs within the
housing, and rubber-mounting the entire compressor unit to the
refrigerator frame.
s In order to create a two-stage compressor, the separate
compressors may be mounted back-to-back such that the
vibration created by one moving mass is cancelled by the other
moving mass. With this two-stage compressor configuration, a
reaction mass is not required
It should be noted that in an alternative embodiment of the
invention, more than one electromagnetic element and armature
element may be used. The use of multiple electromagnetic
element and armature pairs is significant in that it reduces the
mass required to complete the magnetic circuit, without reducing
the area allocated for the flux. Therefore, although the current
and power requirements will increase with multiple
electromagnet pairs and armatures, the total current and power
requirement remains desirably manageable.
Referring now to Figure 3, a second embodiment 120 of the
WO 94/18681 :213 3 ~1 9 4 PCT/US94/01123
compressor valve driver of the present invention is shown. The
compressor shown in Figure 3 utilizes two identical piston drive
assemblies 122, which will be described in more detailed herein .
Each of the piston drive assemblies 122 includes a piston
124, a driver portion 126, a primary spring 132, a secondary
spring 134, and an electromagnetic element 148, comprising an
electromagnetic coil 128 and an electromagnet core 130. The
core 130 has an electromagnet surface or face 138 with an
o opening 164 in the electromagnet surf 138 extending through the
core 130. The opening 164 defines a channel 166. The coil 128 is
disposed in the channel 166.
In the embodiment shown, the piston 124 and driver portion
s 126 are formed as a single assembly of solid low-carbon steel.
The piston is preferably precision machined to in order to provide
close tolerance with the cylinder walls. The close tolerance
serves to minimize - gas leaks around the piston during
compression (referred to as blow-by) during the compression
20 stage. The driver portion 126 is positioned towards the rear end
of the piston drive assembly 122, and includes an armature 168
having an armature face 136. The armature 168 forms a magnetic
circuit with the electromagnetic coil 128 and electromagnet 130.
The armature face 136 and the electromagnet face 138 are
25 dimensioned to correspond and align with each other. As shown in
Figure 3, the armature 168 and the electromagnetic element 148
are annular in cross-section.
In its initial at rest position, the piston drive assembly 122
30 iS biased between the primary spring 132 and the secondary
spring 134 at the midpoint of the piston's travel. When the
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compressor is operating, the piston drive assembly 122
reciprocates at the natural frequency as determined by the
stiffness of the springs 132,134 and the mass of the piston drive
assembiy 122. The electromagnetic circuit maintains the
5 periodic motion by energizing the coil 128 and thereby
accelerating the piston drive assembly 122 each time it passes
through its midpoint during its compression stroke.
Still referring to Figure 3, the operating principle of the
o piston drive assembly is explained. As the electromagnetic coil
128 is energized, magnetic flux lines are generated. An axial
force is generated between the electromagnet 130 and drive
assembly 126 as flux attempts to create a minimum reluctance
path. In the embodiment shown, the minimum reluctance path is
15 achieved when the electromagnet face 138 directly aligns with
the armature face 136. In the embodiment shown, the
electromagnetic face 138 aligns with the armature face at the
peak of the armature's stroke. At this point, the axial force drops
to zero.
If the current in the electromagnetic coil 128 is applied at
the same frequency as the natural mass spring resonance of the
of the piston drive assembly 122 supported between the springs
132, 134, the piston assumes a natural harmonic motion.
During the intake stroke of the piston 124, gas is drawn
into a compression chamber 140, and the secondary spring 134 is
compressed. At the bottom of the stroke, the energy stored in the
secondary spring 134 drives the piston 124 forward, creating
30 positive pressure in the in the compression chamber 140, which,
in turn, closes an intake valve 144. As the gas is compressing
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14
during the forward stroke of the piston 124, it caused an
increased resistance to the piston's motion as the volume of the
compression chamber 140 decreases. The resistance represents
the amount of work performed on the gas during the compression
5 cycle. If no external energy was applied to compensate for the
work performed on the gas, the piston's motion would quickly die
out. However, because the electromagnetic coil 128 is energized
as the piston 124 moves forward in its compression stroke and as
the armature passes through the stroke midpoint, the
èlectromagnetic energy compensates for the compressed gas
resistance and the friction resistance and maintains the piston's
harmonic motion. Once the pressure inside the compression
chamber greater than the high pressure exhaust, an exhaust valve
144 opens, and the gas is pumped out of the compression chamber
15 140 into the exhaust manifold 146.
The energy transferred from the electromagnet 130 to the
piston's motion is a function of the force applied by the
electromagnet 130 and the speed at which the piston is moving
20 when that force is applied. The orientation of the electromagnet
130 in relation to the piston driver portion 126 and armature face
136 allows the maximum force exerted by the electromagnet 130
to correspond to the point of maximum piston velocity.
Therefore, the energy transferred for a given amount of current in
25 the coil 128 is maximized, and the level of current required to
replace the energy lost to the gas during compression is
minimized. Because the power dissipated in the coil 128 is
proportional to the square of the current, (12 R), lowering the
current greatly lowers the dissipated power, which dramatically
30 improves efficiency.
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In order to simplify the electronics required for the
electromagnetically actuated driver 1 20, the mass/spring
resonance of the piston drive assembly 122 is preferably set to
the frequency of the power line voltage, which is typically 60 Hz.
s Due to the weight of the piston drive assembly 122 and the
stiffness of the springs 132, 134, inertial vibration is is
produced by the piston drive assembly 122 as it resonates. In
order to eliminate this vibration, two identical piston drive
assemblies 122a, 122b are mounted back-to-back, as described
o previously herein. The two piston drive assemblies 122a, 122b,
share a common primary spring 132 which biases the piston drive
assemblies 122a, 122b in opposing directions. The two secondary
springs, 134a, 134b, each bias one of the piston drive assemblies
in an opposite direction as the secondary spring. The two piston
15 drive assemblies 122a, 122b, are driven with identical signals.
Therefore, the compressor unit shown in Figure 3 consists of dual
pistons moving 180 degrees out of phase with each other. If the
intake valve 142 and exhaust valve 144 are connected as shown in
Figure 3, the dual piston compressor acts as a single compressor
20 stage, which delivers twice the flow as a single piston. The dual
pistons may also be connected wherein the output of one piston
becomes the input for another piston, creating a two stage
compressor. In the two stage compressor, the volume of the
compression cylinders are adjusted so that the amount of
25 compression achieved by each stage is identical, which balances
the forces to achieve vibration cancellation.
Another feature of the compressor shown in Figure 3 is the
elimination of dynamic seals As shown in Figure 3, the gas
30 intake flows directly into the Intake manifold 150 that surrounds
the two piston drive assemblies 122a. 122b. During the piston.'s
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16
intake cycle gas is drawn into the compression chamber 140 from
the intake manifold 150. During the compression cycle, the
intake valve 142 is closed and the gas is pushed out through the
exhaust valve 144 into the exhaust manifold 146. If a small
5 amount of gas leaks around the piston during compression
(referred to as blow-by) the gas will leak into a central area 162
between the reciprocating piston driver assemblies 1 22a, 1 22b,
through a vent line 164, and into the intake valve manifold
assembly 150. Therefore, even if blow-by occurs, the gas is
o recirculated back into the intake of the compressor.
In the embodiment shown in Figure 3, the compressor
operates in an oil bath, wherein the motion of the reciprocating
pistons circulates the lubricant to the bearing and piston sleeve
s surfaces. The lubricant further serves to transfer internal heat
to the finned compressor case.
There has been described hereinabove an exemplary
preferred embodiment of the actuator according to the principles
20 of the present invention. Those skilled in the art may now make
numerous uses of, and departures from, the above-described
embodiments without departing from the inventive concepts
disclosed herein. Accordingly, the present invention is to be
defined solely by the scope of the following claims.
