BACKGROUND OF THE INVENTION

This invention relates to a refrigeration compressor.

The invention has particular but not exclusive application to an electric motor driven refrigeration compressor and for illustrative purposes reference will be made to such an application. The invention has particular application where an electric motor is included within a closed refrigerant system in circumstances where it is preferable that access to the motor for repairs and/or modification be available without the necessity of entering the closed refrigerant system.

DESCRIPTION OF THE PRIOR ART

In some known refrigeration systems a compressor in the refrigerant circuit is driven by a belt or shaft from a motor external to the refrigerant circuit with the shaft entering the refrigerant circuit through a gland seal. Such arrangements allow the refrigerant to leak from the system in the event of seal malfunction.

Compressors for some other known refrigeration systems, such as domestic and commercial refrigerators, have an electric motor located within a sealed unit from which a discharge line feeds condensed refrigerant and to which the expanded low pressure refrigerant is returned.

Although the environmental requirements to safely contain refrigerants are now well known, the major safeguards against accidental release are directed to operations associated with repairs to the sealed unit and replacement of refrigerant within the sealed system. Accordingly it is prescribed by many governing authorities that such work be carried out in controlled conditions and it is usually a requirement that the refrigerator be removed from its in-situ location to a suitable workshop. Correspondingly, what could otherwise be relatively

inexpensive and simple repairs frequently become relatively complicated, inconvenient and expensive.

Another source of environmental concern is that refrigerants are more likely to leak from refrigerators having aluminium or steel piping for the refrigerant as opposed to copper-tube. Although minor leakage in aluminium- and steel-tube refrigerators is common and is difficult to repair, copper tubing is not commonly used because of its relatively high cost. Furthermore, as gas leaks from the system the cooling capacity decreases. This leads to the compressor operating for longer periods than would be the case if refrigerant had not leaked. This overworking of the compressor in turn leads to the refrigerants and motor coolant oils overheating and this further impairs the efficiency of the system. Moreover, the overheating can cause breakdown of the insulation on the motor coils. Because the coils are housed within the sealed refrigerant system, this breakdown can lead to degradation of the refrigerant and further losses of efficiency. Consequently the compressor is required to work still more constantly and can break down and fail earlier than might otherwise be expected.

When this happens, as has been explained above, repairs are usually both expensive and inconvenient. A high proportion of the breakdowns of compressor units in domestic refrigerators are caused by faults in the electric motor.

In known sealed refrigeration compressor units the compressor is mounted in the sealed housing which itself constitutes an expansion chamber in which refrigerant gases and/or liquid expand after entering the housing through an inlet port. A suction or intake line carries the expanded refrigerant from an intake port located within the chamber to the compressor. Australian patent 509655 is an example of one such prior art compressor assembly.

The refrigerant in known compressors of this type is thus in contact with the electric motor and the coolant oil therefor and in contact with lubrication oil for the

compressor. This contact also leads to contamination of the refrigerant.

Because of the degradation of refrigerant for the various reasons referred to above, it is necessary that the refrigerants be replaced. This results in a build-up of contaminated refrigerants the disposal of which causes problems because of their potential for environmental damage.

A prior art compressor has addressed these problems by interposing a sleeve in the airgap between the stator and rotor. However to reduce degredation of motor performance and efficiency due to the presence of this body in the airgap, such sleeves are very thin and consequently can distend and fail when the refrigerant gases are pressurised. It is required that the compressor sump be depressurised before a stator can be removed from such a sleeve for replacement. Moreover if rotor bearing wear causes the stator to touch the sleeve during rotation, the thin sleeve can be perforated.

SUMMARY OF THE INVENTION

The present invention aims to provide a refrigeration compressor which will be reliable and efficient in use. With the foregoing and other objects in view, this invention in one aspect resides broadly in a refrigeration compressor assembly including:- a housing having input means for receiving refrigerant for compression and output means for returning compressed refrigerant; compressor means mounted in the housing; an electric motor supported by the housing and having a rotor and a stator, the rotor being coupled to the compressor means for rotation thereof; an input refrigerant circuit establishing fluid communication between the input means and the compressor input; an output refrigerant circuit establishing fluid

communication between the output means and the compressor output, and substantially rigid isolating means for isolating the refrigerant from the stator. In a preferred embodiment the isolating means includes a sealed refrigerant unit within the housing. Suitably the compressor means, the input refrigerant circuit and the output refrigerant circuit constitute the sealed refrigerant unit. The assembly may include an expansion chamber for expanding the refrigerant prior to compression. The expansion chamber may be exterior of and in fluid communication with the housing or it can be included within the housing. It is preferred that the input refrigerant circuit includes an expansion chamber within the housing, the expansion chamber including the input means and an expansion chamber outlet in sealed fluid communication with the compressor means. The expansion chamber may include a sump and the expansion chamber outlet may be adapted to drain the sump.

The isolating means may also include a substantially rigid isolation assembly forming with the housing a sealed unit about the compressor means and the rotor. The stator of the electric motor may be mounted independently of the compressor assembly. Thus for example both the stator and the compressor assembly can be fixedly mounted relative to each other by mounting on a common support. However it is preferred that the stator is supported by the housing to enclose the isolation assembly. Suitably the housing includes mounting means for mounting the stator of the electric motor to enclose the isolation assembly.

In a preferred embodiment the isolation assembly includes a substantially rigid cylinder closed at one end thereof and open at the other end for receiving the rotor therein, the cylinder being adapted to abut the stator to form an extension thereof, the gap between the rotor and

the inner surface of the cylinder constituting an airgap for the electric motor.

The cylinder may be made from a non-magnetic material and in one embodiment the cylinder is made of brass. Alternatively the cylinder may be made from a suitable plastics material. However it is preferred that the cylinder includes alternating longitudinally extending strip-like portions of ferro-magnetic material and non¬ magnetic material, the longitudinally extending strip-like portions of ferro-magnetic material being adapted to juxtapose the pole pieces of the stator when the stator is positioned about the cylinder.

The isolation assembly may be supported on the stator or can be adapted for mounting on a support member which also supports the stator and/or the rotor. It is preferred that the isolation assembly includes mounting means adjacent the open end of the cylinder for mounting the cylinder relative to the stator and the rotor. Suitably the mounting means are adapted to mount the cylinder in the housing to extend outwardly thereof. The isolation assembly may also include bearing means on the inner surface of the closed end of the cylinder for supporting the shaft of the rotor.

In a further aspect this invention resides broadly in an electric motor-driven refrigeration compressor assembly including an isolation assembly adapted to abut the stator of the electric motor to form an extension thereof, the gap between the rotor and the inner surface of the cylinder constituting an airgap for the electric motor, the isolation assembly including:- a substantially rigid cylinder closed at one end thereof and open at the other end for receiving the rotor therein, the cylinder including alternating longitudinally extending strip-like portions of ferro-magnetic material and non-magnetic material, the longitudinally extending strip-like portions of ferro-magnetic material being adapted to juxtapose the pole pieces of the stator when the stator is positioned about the cylinder; and

mounting means adjacent the open end for mounting the cylinder relative to the stator and the rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that this invention may be more easily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention, wherein:- FIGS 1 and 2 are representative illustrations of known compressor assemblies for use with a refrigerator;

FIG 3 is an illustration of a compressor assembly having a sealed refrigerant unit within the compressor housing; FIG 4 is an illustration of a compressor assembly having an electric motor including a divider in accordance with the invention and also having a sealed refrigerant unit within the compressor housing;

FIG 5 is a sectional elevation of a compressor assembly having an electric motor including a divider in accordance with the invention; '

FIG 6 is a perspective view of the divider illustrated in FIG 5;

FIG 7 is a perspective view of an alternative embodiment of a divider in accordance with the invention;

FIG 8 is a perspective view of the cylinder portion of the divider illustrated in FIG 7;

FIGS 9 and 10 are sectional elevations of other compressor assemblies having an electric motor with a divider in accordance with the invention;

FIGS 11, 12 and 13 are sectional elevations illustrating modifications to a stator assembly for use with the invention;

FIGS 14, 15, 18 and 19 illustrate alternative embodiments (without the end cap) of the cylinder portion of the divider; and

FIGS 16 and 17 illustrate the component portions used in assembling the cylinder illustrated in FIG 18.

DETAILED DESCRIPTION OF THE INVENTION

As illustrated in FIG 1, a known sealed unit compressor 10 has a compressor 11 and an electric motor 12 for driving the compressor through shaft 13. The compressor is mounted to the underside of a refrigerator with the orientation illustrated by mounting means 17 (shown here as arrows and in practice usually comprising suspended spring mountings) . In this orientation the coolant oil for motor 12 is located in the well portion of the housing. Outlets 14, 15 and 16 are provided in the housing for providing connections to the discharge line, return or suction line and a charge line respectively.

In such a known arrangement the refrigerant gases are not physically separated from the field coils of the stator of the drive motor which with the rotor sit in a well of coolant oil in free contact with the refrigerant gases.

As can be seen in FIG 2, in known refrigeration systems a compressor assembly 70 is connected to a load 71 by refrigerant supply line 72 and refrigerant return line 73. A compressor unit 74 is driven by an electric motor 75 via drive shaft 76. Motor 75 and compressor 74 are mounted within sealed housing 77 in a known manner (not shown) with motor 75 resting in coolant oil 78. Housing 77 has an inlet 79 for receiving refrigerant for compression and an outlet 80 for returning compressed refrigerant to load 71. Refrigerant gases entering housing 77 through inlet 79 expand within the housing which thus acts as an expansion chamber. The refrigerant gases are collected for compression within the housing at inlet 81 of compressor suction pipe 82. Outlet connector pipe 83 carries compressed refrigerant from compressor 74 to outlet 80 for return to load 71.

As can be seen in FIG 3 which illustrates a first embodiment the invention, a compressor assembly 84 is modified from that described above by connecting compressor 74 to inlet 79 by inlet connector pipe 85 and locating an expansion chamber 86 in return line 73. Outlet connector

pipe 83 carries compressed refrigerant from compressor 74 to outlet 80 for return to load 71. Housing 77 is thus not utilised as an expansion chamber and inlet connector pipe 85, compressor 74 and outlet connector pipe 83 constitute a sealed unit within housing 77 physically separating the refrigerant from the electric motor, coolants and lubricants.

Alternatively, as seen in FIG 4 which illustrates a second embodiment of the invention, compressor assembly 87 includes a divider wall 88 forming an expansion chamber 89 within housing 77. Refrigerant entering housing 77 through inlet 79 expands within chamber 89 and is collected within chamber 89 at inlet 90 of inlet connector pipe 91 which passes through a sealed aperture in divider wall 88 and connects inlet 90 in chamber 89 to the inlet of compressor 74. Inlet 90 thus constitutes an outlet of expansion chamber 89 and is in sealed fluid communication with compressor 74. Outlet connector pipe 83 carries compressed refrigerant from compressor 74 to outlet 80 for return to load 71. Housing 77 is thus not utilised as an expansion chamber and chamber 89, inlet connector pipe 91, compressor 74 and outlet connector pipe 83 constitute a sealed unit within housing 77 physically separating the refrigerant from the electric motor, coolants and lubricants. The embodiment of the invention described above may of course be utilised in a conventional compressor assembly as illustrated in FIG 2, or as can be seen in FIG 4, can be included in a compressor assembly also including other embodiments of the invention described subsequently with reference to FIGS 5, 9 and 10. FIG 4 shows a divider 93 sealing rotor 94 from stator 95 in motor 75.

If a lubricant for the compressor is intentionally included in the refrigerant, inlet 90 of inlet connector pipe 91 is preferably located adjacent a wall of chamber 89 such that when compressor assembly 87 is mounted with the motor axis horizontal, inlet 90 is positioned at the lowermost portion of chamber 89 and thus is adapted to collect lubricant for feeding to compressor 74 from the

pool of lubricant collecting at the bottom of chamber 89.

As can be seen in each of FIGS 2, 3 or 4, charge line inlet 92 is respectively located in housing 77 (which constitutes the expansion chamber in known compressor assemblies), or in expansion chambers 86 or 89.

The refrigerant may also be physically separated from the electric motor, coolants and lubricants by the arrangement illustrated with reference to FIGS 5 to 11 which illustrate in greater detail a divider for separating the motor rotor and stator equivalent to that illustrated schematically as divider 93 in FIG 4.

As can be seen in FIG 5, a compressor assembly 20 having an electric motor including a divider in accordance with the invention consists of a compressor housing 21 and a stator housing 22 connected to the compressor housing by bolts 24. Compressor 26 operates in known manner and is mounted on compressor support frame 23 connected to compressor housing 21 by bolts 25. Compressor 26 is driven by rotor 27 when electric power is supplied to stator coils 28 in known manner.

As is best seen in FIGS 5 and 6, a partition between stator and rotor is provided in the form of a cylindrical divider 29 which is positioned between stator 28 and rotor 27 in abutment with the stator to form an extension thereof. Divider 29 is affixed to the interior of compressor housing 21 by bolts 25 together with compressor support frame 23. Divider 29 encases rotor 27 to effectively seal and so separate rotor 27 from stator 28 whereby refrigerant gases are prevented from coming into contact with stator 28 and escaping from the sealed system.

Divider 29 has a central cylindrical body portion 32 open at one end for receiving the rotor therein and closed at the other end by endplate 33. Endplate 33 (as seen in

Fig 9) may support bushes and bearings for mounting one end of the rotor. An annular recess 31 is formed around the open end for receiving stator coils therein when stator housing 22 is affixed to the compressor assembly. Divider 29 also has a peripheral flange 30 extending about the

outer periphery of recess 31 whereby divider 29 is affixed to housing 21 as described above. A gasket (not shown) can be located in known manner between flange 30 and housing 21. It will be realised that the configuration of the divider can vary depending on the type and configuration of the electric motor. Thus, as seen in FIG 10, rotor 42 mounted on compressor housing 40 is separated from stator 43 mounted in stator housing 41 by a divider 44 which does not have an annular recesses to accommodate the stator. Divider 44 merely has a peripheral flange at the open end for attachment to housing 40 as described above with reference to FIGS 5 and 6.

The divider can be made from a non-ferrous and non- magnetic material so that the effects on the characteristics of the motor are minimised. Brass or a plastics material impervious to coolant oils fluids have been found to be suitable materials.

As can be seen in FIG 9, the motor can be extended to provide additional stator coils 45 extending beyond divider

29 for rotation of auxiliary rotor 46 rotatably mounted to the motor housing by bearing 47. Fan 48 is attached to rotor shaft 49. Upon energisation of the motor, rotation of fan 48 provides air cooling of all stator coils. This embodiment illustrates a bearing 96 located on the inner face of the closed end of the divider cylinder and which provides support for the rotor shaft. A bearing may also be mounted on the outside of the endcap as illustarted at

107 to support the other end of the shaft of auxiliary rotor 46.

The effect on motor performance can also be minimised by modifying the stator and divider as now described with reference to FIGS 7 to 11. As is best seen in FIGS 7 and 8, cylinder 51 of divider 50 includes alternating longitudinally extending strip-like portions 53 and 52 of ferro-magnetic material and non-magnetic material respectively. As is best seen in FIG 8 which illustrates cylinder 51 only, the strip-like alternating magnetic and

non-magnetic portions extend only along that portion of cylinder 51 corresponding to the longitudinal axial length of the stator poles. This portion may be separately fabricated and housed in a cylinder 60 made from non- magnetic material and which abuts the end windings of the stator when the stator is assembled about the divider.

Cylindrical portion 60 terminates in opening 61 through which a rotor enters in cylinder 51. The outer end of the strip-like alternating magnetic and non-magnetic portions of cylinder 51 terminate in end plate 33. End plate 33 and cylindrical portion 60 thus reinforce the strip-like alternating magnetic and non-magnetic cylindrical portion of cylinder 51. .

FIG 11 illustrates an end view of a conventional stator 54 having pole pieces 56 and slots 55 for receiving the stator windings (which are not illustrated) through slot openings 57. Stator 54 is modified as seen in FIG 12 by effectively removing the ends of pole pieces 56 by a distance corresponding to the conventional air gap width between stator and rotor. The thickness of the wall of cylinder 51 is equivalent to that of the ends of pole pieces 56, the longitudinally extending strip-like portions of ferro-magnetic material 53 are adapted to juxtapose the pole pieces 58 of the stator when it is positioned about cylinder 51 as seen in FIG 13, and the longitudinally extending strip-like portions of non-magnetic material 52 are adapted to juxtapose slot gaps 59 in the stator. It will be realised that the magnetic flux paths of the motor including a divider in accordance with the invention and having a modified stator with a divider as illustrated in FIGS 7 and 13 are thus not substantially different to the flux paths of a conventional motor without a divider. ** Alternatively to the arrangement described above, the stator 54 may be modified by effectively removing the outer surface thereof by a distance corresponding to the air gap width between stator and rotor.

The correspondence of the flux paths to those of a conventional motor without a divider can be further

improved as illustrated in FIGS 14 and 15 by scoring fine circumferentially extending grooves 97 and 98 around the inside and/or outside surfaces respectively of the cylinder. Grooves 97 and 98 are located to align with the joints of the motor laminae.

FIG 18 also illustrates a divider cylinder 105 made by inserting pole bits 100 in the gaps formed between non - magnetic fingers 99 of former 104 seen in FIG 16. Pole bits 100 are equivalent to the tips of pole pieces 56 seen in FIG 11 and seen as removed in FIG 12. The pole bits 100 may be retained against radial movement when assembled to form the divider by a suitable adhesive. Alternatively the edges of the pole bits may be slightly concave and match slightly convex side edges of fingers 99. As can be seen in FIG 18, the longitudinally extending ferro-magnetic strips 101, 102, 103 etc comprise a series of pole bits 100.

FIG 18 illustrates a modification of the invention in which keyway 106 is formed in cylinder 105 whereby a spline on the stator assembly (not shown) registers in keyway 106 to provide accurate juxtaposition of the stator assembly relative to the longitudinally extending ferro-magnetic and non-magnetic strips on cylinder 105.

FIG 19 illustrates an alternative embodiment of cylinder 108 in which longitudinally extending ribs 109 of non-magnetic material form keyways for closely receiving the poles of a stator assembly.

In order to detect whether the integrity of divider 29 has been breached, a sealed casing can be located about the stator housing in a manner not shown. A pressure sensitive device is located in the enclosure between the outer sealed casing and divider 29 for detecting the resulting increase in pressure if the divider is breached. The pressure sensitive device can be arranged to activate an alarm to indicate that a leak has occurred.

Because of the physical separation of the refrigerant from the housing in which the compressor is located and from the motor, it is possible to use refrigerants other

than those causing environmental damage, but which otherwise could not be used because of the undesirable consequences of their contact with an electric motor, coolants and lubricants. Another advantage of the present invention is that there is no restriction on the orientation of mounting a compressor unit using oil coolant for the motor rather than air cooling, because the oil coolant is physically separated from the refrigerant by the divider. Thus the compressor unit can be bolted horizontally thereby providing greater flexibility in overall refrigerator design.

The compressor housing and the divider in accordance with the invention constitute a sealed unit enabling the stator housing to be replaced without breaching the closed system. The invention thus enables motor failures in compressors to be repaired in a relatively cost effective and timely manner. Furthermore, existing systems can be modified when the first repair is carried out to include a divider and consequently the advantages of the invention are not limited to new installations. An appropriate adaptor kit can be provided which is suitable to enable the connection of a divider to individual compressor semi- hermetic units. Furthermore, in accordance with the invention it is possible to convert sealed compressor units between different voltage systems simply by changing the stator.

It will of course be realised that whilst the above has been given by way of an illustrative example of this invention, all such and other modifications and variations hereto, as would be apparent to persons skilled in the art, are deemed to fall within the broad scope and ambit of this invention as is hereinafter claimed.