Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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IMPROVED REFRIGERATION COMPRESSOR WITH MAGNETIC COUPLING
FIELD OF THE INVENTION
This invention relates to refrigeration compressor units especially but not
exclusively units for small refrigeration units such are suitable for use in
domestic
ice cream makers, small refrigerators and similar appliances. Such units must
be
compact, quiet, reliable and economical to manufacture and operate.
BACKGROUND OF THE INVENTION
Compressor units for domestic refrigerators are commonly of the sealed unit
type
in which both the compressor and a motor permanently coupled to the
compressor are located within an enclosure which is completely and permanently
sealed except for refrigerant connections to the remainder of the
refrigeration
unit. Such a unit has the disadvantages that failure of either the motor or
the
compressor requires both to be discarded, different sealed units are required
for
electrical supplies requiring different motors, even though the compressor is
identical, and two devices, both of which generate unwanted heat, are
thermally
coupled within the same enclosure.
It is known in compressor units for automotive air conditioning systems, which
are engine driven, and thus require a clutch mechanism, to utilize an
electromagnetic clutch between a belt driven pulley and the compressor.
It is also known to use magnetic couplings in drives for pumps so as to avoid
the
necessity of sealing a drive shaft entering the pump chamber. Examples of such
arrangements are to be found in U.S. Patents Nos. 3,584,975 (Frohbieter);
3,680,984 (Young et al.); 4,065,234 (Yoshiyuki et al.); and 5,334,004 (Lefevre
et
al), and in ISOCHEM (Trademark) pumps from Pulsafeeder. Although the first of
the patents relates to a circulation pump for an absorption type air
conditioning
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system, the use of a permanent magnet coupling in the drive to the compressor
of a compress of type refrigeration unit has not to the best of my knowledge
previously been proposed. Reasons may include the sharply fluctuating torque
required by piston type compressors normally used in such systems.
In the interests of smoother and more silent compression, there has been some
adoption of scroll type compressors in compression type refrigeration units,
available for example from Lennox, Copeland and EDPAC International.
An alternative form of piston compressor which has been proposed, although not
to the best of my knowledge for refrigeration applications, is the rotary
piston
compressor using a lobed rotor in a trochoidal chamber and having some
superficial resemblance to rotary piston engines such as the Wankel engine
although the operating cycle is substantially different and the shaft is
driven by an
external power source rather than being driven by the rotary piston. Such
compressors are exemplified in U.S. Patents Nos. 3,656,875 (Luck); 4,018,548
(Berkowitz); and 4,487,561 (Eiermann).
U.S. Patent 5,310,325 (Gulyash) discloses a rotary engine using a symmetrical
lobed piston moving in a trochoidal chamber on an eccentric mounted on a
rotary
shaft and driven through a ring gear by a similarly eccentric planet gear
rotated at
the same rate as the eccentric, the gear ratio of the ring gear to the planet
gear
being equal to the number of lobes on the rotor, typically three. The apices
of the
lobes trace trochoidal paths tangent to the trochoidal chamber wall thus
simplifying sealing. There is no suggestion that similar principles of
construction
could be used in a compressor.
SUMMARY OF THE INVENTION
In its broadest aspect, the invention provides a compressor for a
refrigeration unit
having a stator, a rotor orbiting in engagement with the stator to cyclically
open,
fill with refrigerant gas from at least one inlet port, compress and discharge
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compressed refrigerant gas through at least one discharge port, a rotary drive
for
orbiting the rotor, a driven element of a magnetic coupling in driving
connection
with the rotary drive, a casing sealed save for the ports and enclosing all of
the
foregoing components, a driving element of the magnetic coupling outside of
the
casing in close proximity to the driven element, and means to rotate the
driving
element.
Preferably the rotor is a multilobed rotor orbiting within a trochoidal
chamber
defined by the stator, although a scroll type compressor with stationary and
orbiting scrolls may also be utilized. Most preferably, a three lobed rotor is
journalled on an eccentric carried by a shaft of the rotary drive and has a
ring
gear driven by a gear of the rotary drive having the same eccentricity as the
eccentric and rotated in synchronism therewith, the gear ratio of the ring
gear to
the eccentric being three to one.
1 _5
Further features of the invention will be apparent from the following
description of
a presently preferred embodiment thereof.
SHORT DESCRIPTION OF THE DRAWINGS
Figs 1-4 are cross-sectional views through a compressor in accordance with the
invention, showing different phases of its operation, Fig. 1 being a section
on the
line 1-1 in Fig. 5; and
Fig. 5 is a longitudinal section of the unit on the line 5-5 in Fig. 1, with
the
compressor and drive separated for clarity.
Fig. 6 is a perspective view of an equalizer shaft inserted into the outer
chamber
of another embodiment of a compressor in accordance with the present
invention.
Fig. 7 is a cross-sectional view through a compressor in accordance with the
present invention and incorporating the equalizer shafts of Fig. 6.
Fig. 8 is a cross-sectional view of the connecting chambers of the compressor
of
Fig. 7.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figure 5, a compressor 2 comprises a casing 4 which is completely
sealed apart from input and output pipes 6 and 8 which connect the compressor
2 respectively to the evaporator and the condenser (not shown) of a
refrigeration
unit. A third pipe 10 is used only to charge the unit with refrigerant and is
then
permanently sealed. Internally the pipes 6 and 8 are connected to chambers 12
and 14 respectively (see Figs. 1-4) formed between the casing 4 and a stator
16
of the compressor, the chambers being separated by walls 38. A compressor
drive shaft 18 is journalled in bearings 20 in end walls 22, 24 of the stator,
and
carries at one end a driven element 26 of a magnetic coupling which may for
example consist of concentric rings of ceramic disc magnets 28 having
alternating polarities at their faces adjacent an end plate 30 of the casing
4.
The end plate 30 is secured to a motor casing 32 which mounts a motor 34
coupled to a driving element 36 of the magnetic clutch, which is similar to
the
driven element 26 and supports faces of its magnets 28 adjacent the end plate
30. The coupling may advantageously be designed so that the torque it can
transmit is insufficient to apply damaging overloads to the compressor or the
motor. The motor may be selected to suit the application. For example
alternating or direct current motors for operation at any desired voltage may
be
utilized, or higher or lower speed motors, or variable speed motors to provide
to
provide high, low or variable compressor output. The motor need not be
electric;
for example an internal combustion engine or even a clockwork or manually
powered drive could be used. Since the motor is not within the sealed unit, it
is
simpler to arrange for its cooling, any heat produced can be kept away from
the
compressor, and the motor can be of cheaper construction, as well as being
replaceable.
The compressor 2 utilizes features of construction which resemble features of
the
motor described in U.S. Patent No. 5,310,325, the text and drawings of which
are
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incorporated herein by reference. A trilobar rotor 40 is supported by a
bearing 41
on an eccentric 42 mounted on the shaft 18 for orbital movement along a path
within a trochoidal chamber 44 defined within the stator 16, through which
path it
is driven by an eccentric gear 46 fast on a shaft 48 journalled in the stator
16 by
_5 a bearing 49, which gear engages a ring gear 50 within the rotor 40. The
rotor is
sealed to the end walls 22, 24 by ring seals 51. The shaft 48 is driven by a
belt
52 from the shaft 18, and together with the shaft 18 constitutes a rotary
drive to
the rotor 40 such that the eccentric 42 and eccentric gear 46 rotate
synchronously. The ratio of the ring gear to the eccentric gear is equal to
the
number of lobes, in this case three, of the rotor, and the eccentricities of
the
eccentric 40 and the gear 46 are the same. The stator 16 is formed with ports
54
and 56 communicating with the chambers 12 and 14 respectively. The ports 54
may be equipped with spring valves such as reed valves 58 to prevent unwanted
reverse flow.
Figure 1 shows the position of the rotor 40 when the maximum eccentricities of
the eccentric 40 and gear 46 are directed upwardly (as seen in the drawing).
The direction of rotation in this example is clockwise, and the apices of the
lobes
of the rotor are labeled A, B and C for convenient reference. The geometry of
the rotor and stator and of the drive are such that the apices remain in
contact
with the wall of trochoidal chamber 44. Apex B contacts the wall between the
lower ports 54 and 56, white the surface of the rotor between apices A and C
lies
against the chamber wall, obturating the upper ports 54 and 56. As the rotor
moves clockwise, gas is drawn through the lower port 56 into the chamber
labeled D, while gas in chamber E is compressed and forced out of the chamber
through lower port 54 past valve 58 if its pressure exceeds that in chamber
14.
As the rotor reaches the position shown in Figure 2, apex B moves past lower
port 56 cutting off the induction of gas into chamber D and then apex A moves
past upper port 54 so that gas compressed in chamber D on further motion of
the
rotor can pass through that port once its pressure exceeds that in chamber 14.
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At the same time, that portion of the rotor between apices A and C moves away
from the stator forming chamber F into which gas is induced through upper port
56, and pressurized gas continues to be expelled through lower port 54 from
chamber E.
_5
In Figure 3, the position is analogous to that in Figure 1, except that apex A
lies
between upper ports 54 and 56, and lower ports 54 and 56 are obturated by the
surface of the rotor between apices B and C. In Figure 4 the position is
analogous to that in Figure 2, with chamber F filled, chamber E refilling, and
compressed gas being expelled from chamber D. When the eccentric again
reaches the position shown in Figure 1, the rotor has turned through 120
degrees
and a similar sequence is then repeated. After three sequences, the rotor has
turned through 360 degrees. In effect, three compression cycles are occurring
simultaneously, 120 degrees out of phase, providing high volumetric efficiency
and a very smooth action.
Figs. 6-8 illustrate schematically an improvement to the embodiment
illustrated in
Figs. 1-5. To overcome any unforeseen displacements within the expansion
chamber and to maintain equal pressure during the revolution of the trilobed
rotor. Fig. 7 schematically shows the position of the rotor 40' if there is a
displacement of the expansion chamber 44'. The direction of rotation in this
example is clockwise, and the apices of the lobes of the rotor are labeled A',
B'
and C' for convenient reference. The geometry of the rotor and stator and of
the
drive are such that the apices remain in contact with the wall of chamber 44'.
Fig. 7 illustrates that what happens if there is a displacement of the
expansion
chamber 44', so that one of apices, in the scenario illustrated Apex B', loses
contact with the wall, while the surface of the rotor adjacent apices A' and
C' lies
against the chamber wall. In this embodiment two or more equalizer shafts 70',
71' are inserted within the outer chamber wall 59'. The equalizer shafts
70',71"
are inserted into the chamber wall 59' so that they are able to extend into
chamber 59' to contact the surface of the rotor 40' as it rotates. The
equalizer
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shaft 70' is located in a corresponding recess 72' at the top of chamber 44'
and
equalizer shaft 71' is located in a corresponding recess 73' at the bottom of
chamber 44'. Each of the equalizer shafts 70',71' are biased towards the rotor
40'. In the embodiment illustrated a spring (not shown) is mounted between the
ends 74',75' of the equalizer shafts 70',71' and the back wall 76',77' of
recesses
72', 73'. By maintaining contact with rotor 40' as it rotates, equalizer
shafts
70',71' maintain equal pressure during rotation.
Both equalizer shafts 70',71' are able to extend or retract without acting
under
back pressure caused during the retraction which would otherwise be acting as
a
pump within a pump, causing vibration within the chamber 44'. Both equalizer
shafts are able to retract without creating pressure at the ends 74',75' due
to the
provision of a channel groove 78',79' on rear ends 74',75' and left sides of
the
equalizer shafts 70',71' (see Fig. 6). The rotation of rotor 40' being
clockwise, any
pressure from the chamber 44' entering the equalizer shaft 70',71' is pushed
back through the channel 78',79' on the left side of the equalizer shaft
70',71'
where the pressure volume is at a minimum. As the rotor 40' moves clockwise,
the apices of the rotor 40' push each equalizer spring 70',71' into recesses
72',73'.
While the equalizer shafts 70', 71' are pushed in and out individually, the
refrigerant gas is trapped when the rotor 40' is about to push the volume of
gas
within the chamber 44' through the ports 54,56 into connecting chambers 12 and
14 illustrated in Figs. 1-4. As illustrated in Fig.B, to prevent unwanted
reverse
flow from connecting chambers 12,14 into chamber 44', valve 58 is provided.
Valve 58 can be equipped with a spring valve such a needle valve.
Particularly if at least one of the rotor and the stator is molded from
synthetic
plastic, it may be possible to dispense with apex seals, thus further
simplifying
construction. The use of an external motor means that the latter may also
power
other functions of apparatus including a refrigeration unit incorporating the
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compressor, for example mixing paddles in an ice cream maker. The
compactness of the equipment suits it for use in portable applications such as
refrigerated protective clothing.
Although a particularly preferred embodiment of compressor has been described,
other forms of compressor using rotors orbiting in trochoidal chambers may be
utilized, as may scroll compressors.
