WO2005124246A1

WO2005124246A1 - Refrigeration compressor with magnetic coupling

Info

Publication number: WO2005124246A1
Application number: PCT/CA2005/000930
Authority: WO
Inventors: Peter P.M. Randolphi
Original assignee: Randell, Technologies Inc.
Priority date: 2004-06-16
Filing date: 2005-06-16
Publication date: 2005-12-29
Also published as: CA2471187A1; CA2570971C; CA2570971A1

Abstract

A compressor (101) for a refrigeration unit having a stator (106), a rotor (133) orbiting in engagement with the stator (106) to cyclically open, fill with refrigerant gas from at least one inlet port (103), compress and discharge compressed refrigerant gas through at least one discharge port (104), a rotary drive for orbiting the rotor (133), a driven element (120) of a magnetic coupling (121) in driving connection with the rotary drive, a sealed casing (102) for the ports (103, 104) and enclosing all of the foregoing components, a driving element (125) of the magnetic coupling (121) outside of the casing (102) in close proximity to the driven element (120), a motor (124) to rotate the driving element (125), and at least two equalizer shafts (143, 144) inserted into the chamber (136) and biased towards the rotor (133) to overcome any displacement within the chamber (136) and to maintain equal pressure during the revolution of the rotor (133). The rotor may be a three lobed rotor journalled on an eccentric (135) carried by a shaft (118) of the rotary drive and having a ring gear (139) driven by a gear (137) of the rotary drive having the same eccentricity as the eccentric (135) and rotated in synchronism therewith, the gear ratio of the ring gear to the eccentric being three to one.

Description

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 is located within an enclosure that 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 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 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.

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. Fig. 9 is a longitudinal section of another embodiment of a compressor in accordance with the invention, with the compressor and drive separated for clarity;

Fig. 10 shows two cross-sectional views (reduced) through the compressor of Fig. 9 on the line 10-10 showing different phases of operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 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 it's 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 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 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.

Fig. 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, while the surface of the rotor between apices A and C lies against the chamber wall, obstructing 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 valves 58 if its pressure exceeds that in chamber 14. As the rotor reaches the position shown in Fig. 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. 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.

In Fig. 3, the position is analogous to that in Fig. 1 , except that apex A lies between upper ports 54 and 56, and lower ports 54 and 56 are obstructed by the surface of the rotor between apices B and C. In Fig. 4 the position is analogous to that in Fig. 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 Fig. 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 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.8, 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. Referring to Fig. 9, another embodiment of a compressor according the present invention and embodying the concepts of Figs. 6-8, is generally indicated at 101. The compressor 101 comprises an external casing 102 that is completely sealed apart from input and output pipes 103 and 104 that connect the compressor 101 respectively to the evaporator and the condenser (not shown) of a refrigeration unit. A third pipe 105 is used only to charge the unit with refrigerant and is then sealed. The external casing 102 of the embodiment illustrated has a stator, generally indicated at 106, mounted within the external casing 102. In the embodiment illustrated, stator 106 is connected to external casing 102 at mounting points 107, 108 by a suitable fastener such as screw.

The stator 106, in the embodiment illustrated, has four sections sandwiched together. The first stator section 109 is a generally flat plat section and forms a first outer end 110 of stator 106. The first stator section 109 is sized and shaped so that the first outer end 110 of stator 106 and external casing 102 define an inlet chamber 111. Input pipe 103 and the third pipe 105 are connected to inlet chamber 111. The second stator section 112 is also a generally flat plate section and has two inlet channels 113 in communication with inlet chamber 111 (see Fig. 10). The third stator section 114 is a generally flat ring section. The fourth stator section 115, in the embodiment illustrated, is generally hat shaped and forms a second outer end 116 of stator 106. The size and shape of external casing 102 and the stator sections 109, 112, 114, 115 are selected so the stator fits snuggly against the inside wall 117 of external casing 102.

A compressor drive shaft 118 has a first end 119 journalled through the second outer end 116 of the stator 106 and within the external casing 102 held on the end 119 of shat 118 by nut 126 or other suitable means. The first end 119 of the compressor drive shaft 118 carries a driven element 120 of a magnetic coupling, generally indicated at 121. A motor casing 122 is attached to an end 123 of external casing 102. Within motor casing 122 is a motor 124 coupled to a driving element 125 of the magnetic coupling 121 , which is similar to the driven element 120. The magnetic coupling 121 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 it's 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 drive shaft 118 extends through all four stator sections with a second end 127 journalled through the first stator section and extending into inlet chamber 111. A first gear 128 mounted on the end of drive shaft 118 as in passes through the first stator section engages with a second gear 129 mounted on second shaft 130 journalled through the first and second stator sections offset from the longitudinal axis of the drive shaft 118. Sealing rings 131 , 132 surround the ends of shafts 118 and 130 extending into the inlet chamber 111. A trilobar rotor 133 is supported by bearings 134 on an eccentric 135 mounted on the shaft 118 for orbital movement along a path within a chamber 136 defined within the stator 106, through which path it is driven by an eccentric gear 137 fast on the end 138 of shaft 130 remote from the inlet chamber 111 which gear 137 engages a ring gear 139 within the rotor 133. The ratio of the ring gear 139 to the eccentric gear 137 is equal to the number of lobes, in this case three, of the rotor. The second stator section is formed with outlet ports 140 and 141 communicating with the ends of outlet pipe 104. The ports 140, 141 may be equipped with spring valves such as reed valves 142 to prevent unwanted reverse flow. The direction of rotation in this example is clockwise, and the apices of the lobes of the rotor 133 are labeled A, B and C for convenient reference. The geometry of the rotor 133 and stator 116 and of the drive are such that the apices intended to remain in contact with the wall 142 of chamber 136. As the rotor 133 moves clockwise, gas is drawn through the inlet channels 113 into the chamber 136 on one side of the rotor 133, while gas in chamber 136 on another side of the rotor is compressed and forced out of the chamber through port 140 or 141 past valve 142 if its pressure exceeds that in chamber 136 as described above in connection with the first embodiment.

To overcome any unforeseen displacements within the expansion chamber and to maintain equal pressure during the revolution of the trilobed rotor133, Fig. 10 shows the position of the rotor 133 if there is a displacement of the expansion chamber 136. Fig. 10 illustrates that what happens if there is a displacement of the expansion chamber 136, so that one or more of apices, in the scenario illustrated Apex B and C, loses contact with the wall, while the surface of the rotor adjacent apex A lies against the chamber wall. In this embodiment two or more equalizer shafts 143, 144 are inserted within the wall 145 of the third stator section. The equalizer shafts 143,144 are inserted into the wall 145 so that they are able to extend into chamber 136 to contact the surface of the rotor 133 as it rotates. The equalizer shaft 143 is located in a corresponding recess 146 at the top of chamber 136 and equalizer shaft 144 is located in a corresponding recess 147 at the bottom of chamber 136. Each of the equalizer shafts 143,144 is biased towards the rotor 133. In the embodiment illustrated a spring 150 is mounted between the ends 148,149 of the equalizer shafts 143,144 and the back wall 151 ,152 of recesses 146, 147. By maintaining contact with rotor 133 as it rotates, equalizer shafts 143,144 maintain equal pressure during rotation and prevent leakage of gas around the rotor as noted above in connection with Figs. 6-8

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. However in the preferred embodiment the stator and rotor are made of metal with low expansion-contraction ratios. The use of an external motor means that the latter may also power other functions of apparatus including a refrigeration unit incorporating the 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.

The compressor of the present invention is particularly useful for household in various applications including (but not limited to) consumer household, industrial, portable, transportable, commercial, scientific, medical, environmental and military disciplines. A number of the advantages of the present invention over conventional compressor designs are as follows:

The present inventor has determined a magnetic coupling is optimal for small hermetic refrigerant compressors for the following reasons:

a) it allows the selection and use of AC or DC motors, or other forms of motive power (including clockwork and other motive force mechanisms for remote areas and third world countries) to drive a common compressor design and assembly. Thus a particular or standard hermetic compressor unit can be manufactured in larger quantities, with consequent production savings, for multiple applications simply by changing the external motor, and adding special options as required. External motors are considerably less expensive due to their high production volumes than internal (hermetic) motors that are manufactured in limited quantities.

b) it obviates the generation of heat by the motor inside the hermetic housing, thus making the compressor more efficient by not wasting refrigeration capacity to overcome internally generated heat;

c) it removes the possibility of metal and other residues caused by the friction and wear of an internal motor and bearings, machining fluids, solvents, etc., from contaminating the refrigerant fluid. The magnetic coupling can have multi-segment magnetic wheels (internal and external) that can comprise different amounts of magnetic elements and differing compositions of material of differing magnetic field density, and as a result a certain level of power and torque can be attained depending on the proposed application, the internal working pressure and the gas composition.

The compressors of the present invention preferably feature adjustable torque to optimize or calibrate the refrigeration capacities of certain models, with the added benefit of the "slipping" (as discussed below). Slippage is a safety feature in an effort to improve motor overload situations, such as high-pressure blockage. Additional safety features of this type also help to reduce warranty exposure (cost).

The distance between the inner and the outer discs of the magnetic coupling can be set to enable noiseless operation, and when the magnetic transmission is overloaded it simply slips to prevent motor damage under extreme (accidental or deliberate) conditions of load.

The use of a magnetic coupling allows a certain tolerance in the alignment of the inner and outer wheels, which makes the assembly simpler and cost efficient. The required alignment and construction would pose no more effort than assembly of a conventional refrigerator compressor, particularly when robotic assembly is taken into account. Also, this alignment takes place outside the hermetic chamber and hence is not subject to the stringent cleanliness requirements of a hermetic system.

The losses from electro-motors are converted into warmth, which in the case of internal motors can lead to a loss in performance of up to 22%. An external motor can be cooled environmentally with air, leading to increased effectiveness. Separation of the heat load generated by the motor from the compressor thermodynamics is considered desirable, as well as not using the oil for motor cooling, where metal and other residues caused by the friction and wear of an internal motor and bearings could contaminate the refrigerant fluid.

The design of the present invention makes it easy to change the motor should it fail, and easy to change from use of direct current to alternating current or vice versa, should this be required after a certain period of operation.

Due to the ease of changing from direct current motors to alternating current motors and vice versa, it can be used in a variety of areas (car, bus, train, ship, camping, relaxation, sport, military, etc.) and many international households, commercial and industrial applications for various voltages and frequencies.

For external motors, the concept of the present invention allows for motor control cycles with motor safety functions, which further increases the safety of the compressor and protection of the motor. Modern technology available today permits additional capabilities in general and specific protection methods, such as voltage and current monitoring and limiting. In addition, motor control cycles allow as newer features such as variable speed / variable capacity to provide more precise temperature control and faster reaction times (fast cool down).

With the rotary piston principle, as compared to the reciprocating piston principle, a higher degree of efficiency with fewer vibrations can be expected. A better alignment for both direct current motors and alternating current motors is achieved. Rotary devices inherently have smoother operation than reciprocating devices. This would become more evident when operating the compressor at other than standard speeds (about 3 000 rpm). However, with the advent of optional variable speed motors, higher and lower speeds are possible where the vibration of reciprocating compressors would be more evident. In addition, the appropriate choice of refrigerator capacity, motor power and motor speed could indeed result in greater energy efficiency.

The use of an external motor enables it to be driven by alternative drive sources such as benzene motor or diesel motor or even by hand. In the broad spectrum of applications it is a desirable feature, such as for sensitive medicines that need cooling in remote areas or refrigerated organ transplants - if the power fails, a clockwork mechanism, manually driven refrigeration compressor, solar, wind or hydraulic (water) power, or gasoline or diesel powered motor could save lives. The capability of changing motor drives can be readily accomplished in the field by a technician.

Cost savings are achieved as compared to a built-in motor due to the low purchase and manufacturing price of external drive motors. Comparison of prices for internal (hermetic) motors versus external AC motors indicated that there was a seven times (7X) price difference. Hermetic motors are more expensive in similar quantities (one million) than external motors due to their specialized nature and lower demand. In addition, the cost of manufacturing the compressor itself will be lower by using extrusions rather than castings.

Direct current motors can be easily driven at differing torques under voltage regulations, so that an additional performance level of refrigeration can be achieved using one size of compressor. One of the planned products developed around this compressor has dual application as a household product - for use in the kitchen, as well as to take out in the field on picnics and operate from batteries. This is just one of many applications where DC motors are practicable.

The concept of the present invention offers an additional safety device in the form of transmission slipping when the torque is too high (the inner part of the transmission remains still without causing any damage). The existence of "mature" technologies should not preclude the development of new techniques with added features, particularly with the advent of low-cost "smart" electronics and sensors. One can always revert back to commonplace techniques should practicality and cost factors so indicate.

Additional electronic monitoring and control systems including "soft start" to protect the components (e.g. bearing?) are possible, which increase the working life of the components. Refinements such as "soft start" can be added to modern electronics at very little or no extra cost (often, such features can be incorporated as "firmware" in a microprocessor chip with no actual additional component cost). Where such a feature has more benefit is on variable speed systems where an optional "fast cool-down" mode may mean accelerating the motor from zero to say 6 000 rpm, instead of the standard zero to 3 000 rpm. This can help in the longevity of mechanical parts and bearings.

Two separate compressors with different refrigerants can be driven with one motor, and these can be switched on in succession in order to achieve a lower temperature or higher level of refrigeration performance. If the technical preconditions exist and the applications exist, it can be done, albeit for the more specialized applications. Some applications may be very practical, e.g. in laboratories and hospitals, keeping medicines and samples at appropriate temperatures. Other applications may be more "hedonistic" or for the connoisseur, e.g. keeping a variety of chilled spirits, refrigerated desserts, wines and beers at their most palatable temperatures.

Another use for the compressor of the present invention is in transportable mini- refrigeration systems for various applications.

In a preferred embodiment the compressor is compact, light, small, and can be used as a heating systems by reversing the refrigeration cycle. Using a higher speed motor will achieve a better capacity to weight ratio, and a 50% weight reduction is achievable in such situations, including the motor and magnetic transmission.

The use of higher speed DC motors or variable frequency AC motors can influence the W/Btu/hr energy consumption reducing in to less than 33% of conventional designs. In addition, various zeotropes and azeotropes have been studied in an effort to improve energy efficiency.

The use of novel features such as "soft start" and variable speed/variable capacity temperature regulation removes some of the fixed and transient inertial loads on the system that will serve to enhance the system's life and achieve up to 100% higher length of working life.

The combination of transmission slipping, as well as monitoring and limiting the voltage and current serve to provide a higher margin of safety against accident or abuse.

Although particularly preferred embodiments of compressors have been described, other forms of compressors using trilobar rotors orbiting in chambers may be utilized, as may scroll compressors.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A compressor for a refrigeration unit comprising: a sealed casing having at least one inlet port for receiving refrigerant gas and at least one discharge port for discharging compressed refrigerant gas, a stator enclosed by the sealed casing and defining a chamber in communication with the at least one inlet port and in communication with the at least one discharge port, a rotor enclosed by the sealed casing, the rotor orbiting in said chamber defined within the stator and being in engagement with the at least one inlet port for receiving refrigerant gas and at least one discharge port to cyclically receive refrigerant gas through the at least one inlet port into said chamber, compress the refrigerant gas within the stator, and discharge the compressed refrigerant gas through the at least one discharge port, a rotary drive enclosed by the sealed casing and orbiting the rotor, a driven element of a magnetic coupling in driving connection with the rotary drive and orbiting the rotor, the driven element enclosed by the sealed casing and including at least one magnet, a driving element of the magnetic coupling outside of the casing in close proximity to the driven element, an arrangement for rotating the driving element and at least two equalizer shafts inserted into said chamber and biased towards said rotor to overcome any displacements within said chamber and to maintain equal pressure during the revolution of the rotor.

2. A compressor according to claim 1 , wherein the rotor is a multilobed rotor and said chamber in which the rotor is orbiting is a trochoidal chamber.

3. A compressor according to claim 2, wherein the rotor is a three lobed rotor journalled on an eccentric carried by a shaft of the rotary drive and has a ring gear driven by an eccentric gear, the eccentric gear having the same eccentricity as the eccentric and being constrained to rotate in synchronism therewith, the gear ratio of the ring gear to the eccentric gear being three to one.

4. A compressor according to claim 1 , wherein the arrangement for rotating the driving element includes an electric motor.

5. A compressor according to claim 1 , wherein the magnet includes a plurality of permanent magnets.

6. A compressor according to claim 5, wherein the driving element includes a plurality of permanent magnets.

7. A compressor according to claim 1 wherein the equalizer shafts are mounted in equi-spaced apart recesses within the wall of said chamber.

8. A compressor according to claim 7 wherein a spring is provided between the end of the equalizer shaft and a back wall of said recess to bias the said equalizer shaft towards the rotor.

9. A compressor according to claim 8 wherein a channel groove is provided on one side of the equalizer shafts, and the equalizer shafts are mounted within said recess so any pressure from the chamber entering the equalizer shaft is pushed back through the channel groove on the side of the equalizer shaft where the pressure volume is at a minimum.