GB2292773A - Rotary refrigeration motor/compressor unit - Google Patents

Abstract

In a refrigeration motor/compressor unit the compressor end-plate 2 is made thin so as to respond to pressure differences across it, movements of the end-plate varying the compressor rotor clearance as needed. The moving parts including shaft 10 carrying compressor rotor 3 and motor rotor 14 are lubricated by oil circulating with the refrigerant so that no dedicated oil pump or oil misting device is necessary. The compressor housing 4 and electric motor stator 9 are a close fit within a tubular casing 1. To provide adequate bearing support for the driving shaft 10 bearing 28 and the corresponding part of the compressor housing are of substantial length. The casing 1 includes an off-axis outlet 13 allowing oil to pass from the casing with the refrigerant gas in any orientation of the assembly from substantially horizontal to vertical. The motor/compressor unit may be incorporated in a refrigeration or air-conditioning system including a desuperheater heat exchanger 27. <IMAGE>

Description

DESCRIPTION OF INVENTION Title: "Rotary Refrigeration Motor/Compressor" THIS INVENTION relates to a motor/compressor for use in refrigeration or air-conditioning apparatus - such as household/commercial refrigerators, freezer-cabinets, icemakers, air-conditioning units and heat-pumps etc.

It is among the objects of the invention to provide an improved refrigeration motor/compressor.

Hermetic motor/compressors are known per se in refrigeration and air-conditioning systems. Such motor/compressors are hermetic in the sense that the moving parts are wholly contained within a hermetically sealed casing which communicates with and forms part of the refrigeration circuit around which a refrigerant gas is caused to circulate, in a closed circuit, by the motor/compressor.

According to one aspect of the invention there is provided a rotary refrigeration motor/compressor in which an elastic lateral inward flexing movement of the compressor end-plate is possible sufficient to improve the compressor volumetric efficiency by automatically reducing the clearance of the compressor rotor in the chamber and thereby improving the hydrodynamic gas-sealing at both sides of the compressor rotor, as the motor/compressor casing pressure rises.

In a motor/compressor embodying this aspect of the invention, the greatest reduction in clearance volume occurs when extra compressor capacity is most needed i.e.

when the motor/compressor is operating under high ambient temperature/pressure conditions.

According to another aspect of the invention, there is provided a rotary refrigeration motor/compressor in which an elastic lateral outward flexing movement of the compressor end-plate is possible and is utilised to control refrigerant liquid "flood-back" difficulties, when starting, by automatically increasing the clearance of the compressor rotor in its chamber under "flood-back" conditions, whereby a sudden increase in hydraulic pressure in the compressor chamber can be relieved by outward flexing of the compressor end-plate.

In a motor/compressor unit embodying this aspect of the invention, under "flood-back" conditions the liquid refrigerant is forced past the compressor rotor gas sealing surfaces and it does not damage to the motor/compressor.

According to yet another aspect of the invention there is provided a compressor for a gaseous medium including a compressor with a cylindrical housing defining a working chamber, a member movable in said working chamber for pumping the gaseous medium, a driving shaft operatively connected with said movable member and rotatable in a bearing and means in said compressor housing to drive said movable member, and wherein the compressor and an electric motor for driving the compressor are enclosed in a sealed casing, the electric motor including a stator and a rotor, said movable member of the compressor comprising a compressor rotor mounted on said shaft at one end thereof, the electric motor rotor being mounted at the other end of said shaft, with said bearing being disposed between the motor rotor and said compressor rotor and said cylindrical compressor housing and said electric motor stator being fitted coaxially with said casing, and wherein said bearing means comprises a single long plain bearing provided in an integral extension of said cylindrical compressor housing which provides said working chamber.

In a refrigeration system incorporating a hermetic motor/compressor, any provision made for lubrication of moving parts relative to adjoining stationary parts must likewise be hermetically sealed within the system.

Conventionally, a lubrication system is adopted which includes an oil sump formed by part of the motor/compressor casing and an oil pump driven by, and indeed generally formed by, part of the motor/compressor for pumping oil from the sump to the bearings and other sliding surfaces of the compressor, from whence the oil returns to the oil sump. However, the provision of such a sump and oil pump arrangement means that the motor/compressor incorporated in such an arrangement must be installed in a predetermined orientation relative to the horizontal or that, at least, permitted deviations from such predetermined orientation are relatively small.Furthermore, the construction of such known motor/compressors is generally such that the motor/compressor must be mounted with its rotary axis vertical and since such motor/compressors are generally elongate in the direction of their longitudinal axis, this means that such a motor/compressor must be of substantial height. Such motor/compressors are generally mounted at the rear or end of conventional refrigerator cabinets at the bottom of such cabinets and the design of a refrigerator cabinet to accommodate a motor/compressor of substantial height normally entails the loss of useful storage space.

According to another aspect of the invention, there is provided a refrigeration motor/compressor including a compressor housing defining a working chamber, a member movable in said working chamber for pumping gaseous refrigerant, a driving shaft operatively connected with said movable member and rotatable in bearing means in said compressor housing to drive said movable member and means for maintaining an oil mist in the refrigerant, the arrangement being such that, in operation, oil from said oil mist can reach said bearing means for lubricating said bearing.

As is well known in the refrigeration industries the refrigeration oil, being miscible with the refrigerant, normally circulates throughout the refrigerating circuit when the compressor is running. In a preferred refrigeration or air conditioning system embodying the invention, therefore, in which compressed and subsequently condensed refrigerant is passed through a capillary tube or expansion valve into an evaporator, in manner known per se, the considerable pressure drop across the capillary tube 66 (in the order of 150 to 250 p.s.i.) causes oil frothing at the capillary tube outlet. This oil froth is further ebbulated by the boiling liquid refrigerant in the circuit evaporator. The refrigerant gas from the evaporator carries the oil as a mist into the compressor.

According to a yet further aspect of the invention, there is provided a motor/compressor for refrigeration or air-conditioning purposes, comprising a compressor housing, a compressor rotor rotatable in the compressor housing and carried by a shaft extending through the compressor housing and supported by a bearing in said compressor housing, the shaft at its end remote from the compressor rotor carrying the rotor of an electric motor positioned within an electric motor stator, said compressor housing and said electric motor stator being disposed at different axial locations within a sealed tubular casing, and each being a close fit within said casing whereby the casing serves to hold the electric motor stator and the compressor housing in axial alignment with one another.

According to a still further aspect of the invention, there is provided a refrigeration circuit or air-conditioning system including a circuit for refrigerant gas and oil and a motor/compressor in said circuit for pumping the refrigerant and oil around said circuit, wherein said circuit includes a hermetic casing containing said motor/compressor, the casing being so arranged that the exit from said casing, in said circuit, for the refrigerant, is disposed at substantially the lowermost point in said casing, to ensure that oil draining within the casing is discharged therefrom with the refrigerant gas, in operation of the circuit.

In a preferred embodiment of the invention, a refrigeration hermetic rotary motor/compressor is provided which can be installed at any angle from the vertical position to 2 degrees from the horizontal plane.

The motor/compressor in this embodiment is intended to be utilised in factory assembled, self-contained refrigeration products or air-conditioning units. These factory assembled products and units have air-cooled condensers, and they should be designed to operate quietly and reliably with good BTU-per-WATT ratios, particularly when operating in high ambient temperatures.

The preferred embodiment operates efficiently with a "dry oil sump" lubricating system when the motor/compressor is running. The ebbulated lubricating oil circulates with the mobile refrigerant throughout the hermetic refrigeration circuit in a frothy, globule/mist form. A lubricating oil pump and oil reservoir are not required with the "dry oil sump" method of oil-entrained suction gas compressor lubrication.

In a preferred embodiment, extended centring guides or ribs are moulded to the cylindrical compressor housing.

The centring guides assist assembly of the motor/compressor, and they also act as shaft bearing heat dissipating fins.

The preferred refrigeration circuit, embodying the "dry oil sump" lubricating system includes a motor/compressor cooling system which incorporates a compressor discharge gas desuperheater. This desuperheater lowers the temperature of the compressor discharge gases and the entrained oil globules before they enter the motor/compressor casing. In the preferred refrigeration circuit the compressor motor and its shaft bearing are cooled by the desuperheated discharge gases and the entrained lubricating oil. Motor cooling, and shaft bearing cooling is achieved without raising the temperature of the compressor suction gas. The waste heat from the compressor motor is absorbed by the desuperheated discharge gases, and it is then rejected by the condenser of the refrigeration unit.

Hot discharge line gases are sometimes used in conventional refrigeration units to pan-evaporate condensate whilst such gases are on their way to a refrigerator condenser. This saves running a condensate drainpipe. Hot gases from the compressor are also sometimes used to heat a domestic hot water cylinder.

Again, these gases normally continue on their way to the refrigerator unit condenser, after giving up some of their heat to the water. However it has not hitherto been proposed to return such gases, after cooling in either of these ways, to the motor/compressor casing. Some large and medium sized conventional motor/compressors are fitted with remote oil coolers. The preferred embodiment does not require a special oil cooler, as the discharge gas desuperheater also cools the lubricating oil.

Most conventional motor/compressors utilise the compressor suction refrigerant gas to cool the motor windings. This is currently accepted, but it is undesirable, because the suction gas temperature is raised, and this results in high discharge gas temperatures. Also, a superheated suction gas lowers the compressor efficiency (and the overall unit efficiency) i.e. it lowers the BTUper-WATT ratio of the unit.

High compressor discharge gas temperatures in conventional hermetic compressors have caused numerous motor/compressor "burn-outs" and this is a costly problem for the refrigeration industries. Thousands of "burnt-out" motor/compressors have been returned to the manufacturers.

By cooling, by means of a desuperheater, the compressor discharge gases rather than the compressor suction gases, and using the desuperheated discharge gases to cool the compressor/motor, the above disadvantages are avoided.

The overall BTU-per-WATT ratio of a conventional refrigerating unit is considerably improved by the addition of a discharge gas desuperheater and the preferred discharge gas compressor motor cooling system. In the preferred embodiment of the invention, the compressor discharge temperature is lowered by the air cooled desuperheater, and the compressor motor waste heat losses are not added to the suction gases.

Oil lubrication of the compressor and the shaft bearing is also assisted by the lower temperature of the desuperheated compressor discharge gas.

Embodiments of the invention are described below by way of example with reference to the accompanying drawings, in which: FIGURE 1 is a longitudinal sectional view through a motor/compressor embodying the invention when it is positioned with its rotational axis at a 2 degree angle with respect to the horizontal, FIGURE 2 is a view in cross-section on the line II II of Figure 1, FIGURE 3 is a view in cross-section on the line III-III of Figures 1, through the bearing oil port, FIGURE 4 is an axial section view of a hermetic motor/compressor embodying the "dry oil sump" and desuperheated compressor discharge gas motor cooling features of the invention; FIGURE 5 is a view in cross-section along the line A-A of Figure 4;; FIGURE 6 is a view in cross-section along the line B-B of Figure 4 but showing an alternative mounting arrangement and an alternative clamping arrangement for the hermetic motor/compressor; FIGURE 7 is a side elevation view of the hermetic motor/compressor of Figure 6; and FIGURE 8 is a schematic diagram of a complete refrigeration system utilising the motor/compressor.

The drawings illustrate refrigeration hermetic motor/compressors embodying the invention, intended to be used for self-contained refrigeration appliances and airconditioning units. The drawings also show parts of the associated appliance or air-conditioning units.

Referring to Figures 1 to 3, a single-stage, 2 pole, single phase, rotary, hermetically sealed motor/compressor is shown which can be mounted in the vertical position - or a 20 angle from the horizontal plane, or at any angle between these two positions. The motor/compressor has been designed for use in personal coolers, dehumidifiers, domestic refrigerators, air conditioners, cooling cabinets, bottle dispensers, freezing chests, liquid coolers, ice-makers and the like.

A rotating-vane type of compressor is preferred for the invention, but a scroll compressor may be used in the machine, instead of a rotating-vane compressor. A conventional vapour compression refrigeration cycle is used with the motor/compressor.

Figure 1. The motor/compressor is enclosed in a hermetically sealed, tubular, cylindrically shaped casing 1. The preferred refrigerant is H134a - or a similar nontoxic refrigerant may be used in the refrigeration system.

The compressor oil circulates throughout the refrigeration system with the refrigerant in the usual manner. No oil reservoir, oil pump, or special oil misting device is fitted, as these are not considered necessary for the motor/compressor.

A "remotely fitted" air-cooled discharge gas desuperheater 27 is to be used with the motor/compressor for the purpose of lowering the compressor discharge gas temperature. The desuperheated discharge gas and oil globules are blown into the motor/compressor casing through connection 7, and they cool and lubricate the shaft bearing 28. These discharge gases cool the electric motor windings as they pass through the stator lamination grooves 8 and the motor stator/rotor gas-gap 16. A "dry-oil-sump" is used in the motor/compressor. The discharge gases and oil globules then blow out of the casing via outlet pipe connection 13 to a "remote" condenser (not shown). This arrangement is similar to that disclosed in the co-pending McDonald U.K. Patent Application No. 9506016.6 dated 24th March 1995, to which reference should be had.

The compressor end of the machine is referred to herein as the upper-end, and the motor end is referred to as the lower end.

If the chosen compressor is of the Rotating-Vane typeXFIGS. 1 and 2),it may have 2, 3 or 4 vanes, with a single or double-lobed stator. The compressor stator casting 4 incorporates the elongated plain motor shaft bearing 28 including the centering/supporting fins 5, and it is moulded and machined as one component, for accurate alignment. The preferred rotating-vane motor/compressor has two rotor vanes and a single-lobed compressor stator4. The discharge gases and oil globules pass through the ball type discharge valve 22 to the desuperheater 27. The gases and oil globules return from the desuperheater and evaporator (not shown) to the compressor via suction pipe 18 and connector 24.

A feature of the invention is the thin compressor end-plate 2.

The thin end-plate design allows for a minuscule amount of end-plate elastic movement to take place, as the casing pressure varies. When operating, the motor/compressor casing pressure is about five pounds per square inch lower than the compressor discharge pressure (which may frequently be over 200 P.S.I.G). After the compressor stops running the pressures in the refrigeration system rapidly equalise. The compressor end-plate then returns to its normal unpressurised position, and the clearance between the end-plate and the compressor rotor increases - enabling the compressor motor to start virtually unloaded.

On 'start-up ' the compressor discharge pressure gradually rises and the motor/compressor casing pressure increases.

Simultaneously, the suction pressure of the compressor is decreased, and therefore the pressure difference across the end-plate increases. This pressure difference across the end-plate is sufficient to move the central portion of the end-plate a minuscule amount inwards towards the compressor rotor 3 and thus reduce the clearance between the side of the compressor rotor and the end-plate. The clearances on both sides of the compressor rotor are reduced, as the driving shaft/rotor combination is free to move in the direction of its axis. Shaft end-play is controlled by the compressor A side-clearances. A very thin annular shaped gasket may be fitted between the end-plate and the compressor stator. The end-plate material is well within accepted 'modular of elasticity limits' as less than two thousandths of an inch lateral movement of the central portion of the end-plate is required.The two hydrodynamic gas-sealing sides of the compressor rotor prevent excessive elastic movement of the end-plate.

A supplementary oil lubrication system is provided. Oil is forced along the close-fitting shaft bearing to the rotor sides by the high casing gas pressure. Some of this oil passes through the gas sealing sides of the rotor, and it provides extra cylinder lubrication. Excess oil passes through the compressor discharge valve, and it then circulates through the refrigeration system with the refrigerant in the normal manner.

Clamping bands 30 are fitted externally to the motor/compressor casing as disclosed in McDonald U.K.

Patent Application No. 9506016.6 dated 24th March 1995.

The compressor stator 4 and the electric motor stator 9 are sliding fits in the tubular casing, and these two components are held in place by two or more clamping bands.

The clamping bands assist assembly of the motor/compressor in the factory, and they also constrict the relatively high discharge gas pressure in the casing. The clamping bands obviate the need for bolting or welding the compressor and motor stators to the casing. The motor/compressor of the invention uses externally located anti-vibration mountings 15. These mountings may be attached to the clamping bands.

The electric motor driving shaft 10 has a compressor rotor 3 at its upper-end, and a motor rotor 14 at its lower-end. An overload protector cut-out 29 is imbedded in the motor windings.

The driving shaft has a machined helical oil groove 17, and an oil retaining weir 31 is fitted to the driving shaft bearing 28.

The small diameter of the motor/compressor casing enables it to be more easily assembled into appliances such as Personal Coolers and room Dehumidifiers, which have space limitations.

In the motor/compressor of the invention the clearance volume of the compressor is automatically reduced when extra compressor capacity is most needed i.e. when the motor/compressor is operating under high ambient temperature conditions.

The electric terminal block and cover 12 is normally positioned at the lower-end of the casing. An alternative position for the terminal block and cover is 26. The motor leads may be brought up through the two compressor stator ports 18.

The motor/compressor of the invention is particularly suitable for refrigeration and air cooling applications which require a low noise level. The discharge gas pulsation noises are dampened in the 'remotely installed' desuperheater and the hermetic motor/compressor casing.

FIG. 2. The refrigeration piping connectors 22 and 24 have oil sealed threads, and the connectors are welded or brazed to the casing. The small, spring-loaded spherical discharge valve may be made from any suitable material such as steel, carbon etc. No suction valve is fitted, as a suction valve is not considered necessary for the compressor.

The motor/compressor can be used with either capillary tube or expansion valve refrigerant flow controls. Conventional defrosting systems may be used with the motor/compressor.

Referring to Figures 4 to 8, the motor/compressor shown comprises a conventional twin vane rotary compressor and an electric driving motor enclosed in a thin-walled, hermetically sealed casing 58 in the form of a tubular body fitted with two welded end caps 58 and 90.

The compressor includes a generally cylindrical compressor rotor 60 at one end of a driving shaft 62 integral with the rotor 60 and coaxial therewith and a compressor housing 64 in which the rotor 60 and driving shaft 62 are rotatable. The compressor housing 64 comprises a unitary body having a cylindrical cavity 66 extending from an end face of the unitary body and having a cylindrical bore 68 extending through the remainder of said unitary body from the inner end of said cavity 66.

The shaft 62 extends from compressor rotor 60 through the bore 68, which forms a plain bearing for the shaft 62. The axial depth of cavity 66 corresponds substantially with that of rotor 60 which is a close rotating fit between the inner end of cavity 66 and the opposing surface of a flat end plate 70 secured to said end face of the compressor housing body 64 by set-screws 72, the cavity 66 defining, with the end plate 70, a working chamber for the rotor 60.

The length of bore 68 is over twice the axial length of cavity 66.

The shaft 62 projects from the end of the compressor housing body 64 remote from end plate 70 and carries, at its end remote from the compressor rotor 60, a rotor 74 of the electric motor. The motor rotor 74 rotates within the stator 75 of the motor. The radially outermost parts of the periphery of the compressor housing body 64 lie upon a notional cylindrical surface coaxial with the bore 68 and which is closely engaged by the cylindrical internal surface of tubular casing 58 whereby the compressor housing 64 is maintained coaxial with the tubular casing 58. The motor stator 75 likewise has a cylindrical peripheral surface which closely engages the cylindrical surface of casing 58 wherein the stator 75 is likewise maintained coaxial with casing 58 and with stator 64.

The motor rotor 74 is secured to the shaft by means of a well secured set-screw 77. The compressor rotor 60 and its integral driving shaft 62 are of hardened steel.

The compressor housing 64 may be of cast iron although it is possible to form this component of a suitable plastics material.

In manner known per se, the cylindrical cavity 66 is eccentric with respect to the bore 68 so that, as shown in Figure 5, the compressor rotor 60 is in sealing contact with the wall of cavity 66 at one position around the periphery of cavity 66 and is spaced therefrom by a variable amount at other circumferential positions. An inlet port communicating with an inlet pipe 76 and an outlet port, communicating with an outlet discharge valve 28 are provided in the wall of cavity 66 on respective sides of the region of sealing contact between the compressor rotor 60 and the cavity 66. The discharge valve 78 may be of the ball type, as illustrated, or of the reed type.

The compressor rotor 60 has, on diametrically opposite locations, two radial slots extending over the length of the compressor rotor 60 and which receive, as a close sliding fit, respective vanes 80 which are also a close sliding fit between the inner end of cavity 66 and the opposing surface of end plate 70. In operation, the vanes 80 are urged radially outwardly, by gas pressure and centrifugal force, against the peripheral wall of cavity 66 whereby, as the compressor rotor rotates, refrigerant is drawn in through the inlet port at relatively low pressure and is pumped out at relatively high pressure through the outlet port. A compressor arrangement of this kind is known per se. The twin vane compressor rotor may be replaced by a scroll type of compressor, also known per se.

The motor/compressor shown, when used in a refrigerator or air-conditioning unit, draws into the compressor, via inlet 76, refrigerant which has passed from the cold side of the refrigeration circuit, having absorbed heat from the interior of the refrigerator or from the airconditioning space, compresses the refrigerant and pumps it out through discharge valve 78 from where the refrigerant passes to a heat exchanger constituting a discharge gas desuperheater 82 (shown only schematically in Figures 4, 5, 6 and 7) which serves to cool the refrigerant which has become heated by compression in the compressor. From the desuperheater the refrigerant is discharged at medium velocity to enter the casing 58 via an inlet 84.

Relatively high refrigerant velocities are used in the unit components, and only a very small refrigerant charge is required in the refrigeration unit shown in Figure 8.

The desuperheated refrigerant gas then passes through the interior of the casing 58, serving to cool the electric motor and the driving shaft bearing 68, before exiting from an outlet 86 from whence it passes to a further heat exchanger or condenser 108 (Figure 8) where it is cooled to close to ambient temperature and is therefore caused to liquify before passing through a strainer 107 and a capillary tube 106 into an evaporator 105 forming the cold side of the refrigeration circuit. In operation, the electric motor rotor rotates at two-pole motor speed and acts as an efficient circulating fan to circulate the refrigerant gas within the casing 58.

In contrast with known arrangements, the motor/compressor illustrated does not incorporate an oil sump for lubricating oil, nor an oil pump for pumping oil to the bearing 68. Instead, the motor/compressor relies, for lubrication of the shaft 62 and bearing 68, compressor rotor 60 and vanes 80, on oil carried around the refrigeration circuit with the refrigerant and which oil is to a large extent in the form of an oil froth or mist. The refrigerant returning from the desuperheater 82 is at substantial pressure and enters the casing 58 through an inlet 84.The desuperheated gases entering the casing through inlet 84 contain oil globules, and the piping connected with the casing at inlet 84 is pointed in the direction of oil lubrication bores 65 (see below) in the shaft bearing, the velocity of the gases entering via inlet 84 being sufficient to spray the bores 65 with oil (even when the motor/compressor is vertically mounted).

The preferred refrigeration circuit shown in Figure 8 and embodying the "dry oil sump" lubricating system includes a motor/compressor cooling system which includes the compressor discharge gas desuperheater 82. This desuperheater lowers the temperature of the compressor discharge gases and the entrained oil globules before they enter the motor/compressor casing 58. In the preferred refrigeration circuit the compressor motor and its shaft bearing 68 are cooled by the desuperheated discharge gases and the entrained lubricating oil. Motor cooling, and shaft bearing cooling is achieved without raising the temperature of the compressor suction gas. The waste heat from the compressor motor is absorbed by the desuperheated discharge gases, and it is then rejected by the condenser of the refrigeration unit.

Desuperheating the discharge line gases makes inter-cooled two or three stage compression possible, in the one motor/compressor. Two/three stage compression is more efficient, and it is particularly desirable for lowtemperature, high compression-ratio appliances such as low ambient temperature heat pumps, freezer-cabinets, icemakers, large household/commercial refrigerators etc.

Different model motor/compressors would be required for high ratio-of-compression applications. Two or three stage motor/compressors may be similar in design to the single stage motor/compressor described with reference to the drawings herein, but larger in size. Two and three stage intercooled compressor rotors may be provided which will fit neatly on to the upper end of the compressor. The electric motors for such multi-stage motor/compressors will, of course, be larger than for corresponding single stage motor/compressors. It is envisaged that motor/compressors could be made up to 10HP size, and possibly up to 100HP size.

Oil droplets in the oil mist which strikes surfaces within casing 58 tend to coalesce into an oil film which drains into the lower parts of the interior of casing 58 (and which film also, of course, is responsible for the desired lubrication of bearing 68, compressor rotor 60 etc). The oil so draining is readily propelled by the discharge gas pressure as intermittent "slugs" of oil, from the outlet 86, through the relatively small diameter tubing which forms the major part of the refrigeration circuit.

With the lubrication arrangement described, only a very small oil charge is needed because no oil reservoir is utilised.

A conventional suction/liquid line refrigerant heat exchanger 121 may be provided - also a conventional suction line strainer/accumulator 120 as shown in Figure 8 may be included.

As shown in Figures 4 and 6, a longitudinal groove 87 is formed along the periphery of the electric motor stator 75 at the lowermost part of the stator in order to allow oil to drain, and be blown past the stator 75 from locations within the casing 58 forward of stator 75. A similar groove 87 may be formed along the periphery of the compressor housing 64 to allow passage of gas between the region in front of the compressor housing 64 and the region behind, to ensure that any oil which may have gathered in the portion of casing 58 in front of the compressor housing 64 (for example during storage or transportation of the unit) can likewise drain past the compressor housing 64.

When the motor/compressor is installed in the vertical position, oil will also be blown down the motor rotor gas-gap 119 by the refrigerant, as it passes to outlet 86.

The casing 58 comprises a length of thin walled cylindrical steel tubing closed at the end adjacent the compressor (herein referred to as the front end of the motor/compressor) by an end cap 88 and at the end adjacent the electric motor (herein referred to as the rear end of the motor/compressor) by an end cap 90.

The outlet 86 is provided by the end cap 90 at a location which is below the lowermost part of the interior of the tubular part of casing 58 when the latter is mounted with the rotary axis of the motor/compressor horizontal and in such an angular orientation about said axis as to obtain the lowest position for the outlet 86. In practice, and as illustrated, it is preferred to mount the motor/compressor so that the rotary axis of the motor/compressor is at a slight angle of, for example, 2 degrees to the horizontal, with the rear end of the motor/compressor being lower than the front end, in order to allow oil draining within the casing to flow towards the rear end, the angular orientation of the motor/compressor about its axis being again such as to place the outlet 86 lowermost.As shown, the cap 90 is so formed that the outlet 86 is displaced further from the central axis of the motor compressor than the adjoining part of the rim of cap 90, and that the interior of the cap 90 slopes smoothly from said rim part of the outlet 86. Furthermore, the major part of the cap 40 forms a pan which is inclined, relative to a diametrical plane, away from the remainder of the casing in the direction towards outlet 86 from the parts of the rim of cap 90 remote from outlet 86. This configuration of end cap 90 ensures reliable drainage of oil within the casing to outlet 86 when the motor/compressor is mounted with its central axis vertical or in any of a range of possible orientations of said axis between vertical and near horizontal.

Most of the entrained lubricating oil mist/globules drawn into the compressor cavity 66 via inlet pipe 76, with the refrigerant gas, pass through the compressor with the refrigerant gas. The remainder of the oil flows along the shaft bearing 68 under the influence of the pressure of the refrigerant compressed in cavity 16 between compressor rotor 60 and the cavity wall, by the two vanes 80. A helical groove 63 is machined in the periphery of the compressor motor shaft 62 to assist oil-flow along the bearing 68.

The forward portion of the compressor housing 64 in the immediate vicinity of the cavity 66 provides a substantially continuous surface engaging the interior of the tubular casing 58. In order to secure accurate centring of the compressor housing 64 with respect to casing 58 and at the same time to improve the rigidity of the bearing 68, the compressor housing body 64 includes six ribs or fingers 92 which extend rearwardly from the forward portion of the compressor housing 64, i.e. in a direction away from the cavity 66 and which have limiting outer surfaces which are a continuation of the cylindrical peripheral surface of the forward portion of the compressor housing body 64, as shown in Figure 6.In order to minimise weight, assist cooling and allow circulation of refrigerant and oil mist, the ribs 92 are relatively narrow in the circumferential direction and are spaced apart regularly about the central axis of the motor/compressor, as shown in Figure 6. The bearing 68 is provided in a central portion 94 of the compressor housing body 64 extending rearwardly from the forward portion and the rearward part of such portion 94 is connected by integral radially extending portions 96 with the rearward parts of ribs 92. These radially extending portions 96 thus form a kind of "spider" bracing the free end of the portion 94 with respect to the peripheral part of the compressor housing 64.Viewed in another way, the rearward region of the compressor housing 64 may be regarded as comprising a plurality of webs 92 extending radially from an axial central core containing bore 68 and extending also longitudinally of the compressor housing, these webs 92 terminating in radially outmost part-cylindrical surfaces engaging the cylindrical of casing 58, each web 92 further having an aperture 98 (see Figures 4 and 6) formed transversely therethrough between its peripheral surface and the axial core, intermediate the rear end and the forward part of the compressor housing 64. Indeed the apertures 98 could be dispensed with and the webs 92 made solid or each such web 92 could have a plurality of apertures therethrough instead of a single aperture 48.

The compressor housing part 64 and electric motor stator 75 are a tight interference fit in the tubular casing 58, allowing for accurate centring of the compressor housing 64 and stator 75 in the casing 58 whilst still allowing easy assembly. Radial bores 65 are formed through the central portion 94 on its upper side, communicating with bore 68 whereby oil settling on the upper surface of portion 94 can run or be blown by the desuperheated gas into bore 68.

The accurate centring of the compressor housing 64 with respect to casing 58 and the length and rigidity of bearing 68, combined with accurate centring of the motor stator 75 in casing 58 allows accurate centring of the electric rotor 74 in stator 75, if the shaft 62 is made an accurate close fit in bearing 68. This in turn allows the gas-gap between the electric motor rotor 74 and stator 75 to be minimised, to maximise motor efficiency. The length of the bearing 94 allows the shaft 62 to be of relatively small diameter.

The hermetic motor/compressor casing of the invention acts as a discharge gas noise muffler, and the casing surface also dissipates waste heat to the surrounding air, (see Figure 7).

Higher BTU-per-WATT figures are obtained, as compared with a conventional motor/compressor, from the single compressor stage motor/compressor shown in the drawings, by passing the desuperheated gases back to the casing for shaft bearing and motor winding cooling. The higher BTU-per-WATT gain is obtained by not using the compressor suction gases for motor winding cooling, as happens in most conventional refrigeration motor/compressors.

As mentioned previously, superheating the compressor suction gases lowers the compressor efficiency (because of the increase in the specific volume of the gases being compressed). Excessively superheating the compressor suction gases also creates higher compressor discharge line temperatures, with resulting problems.

In manufacture of the motor/compressor, the assembled compressor, and electric motor stator and rotor are inserted in the desired orientation in the tubular part of the casing 58. Two strong clips or clamping bands 100 are then fitted externally around the casing 58 to clamp the tubular casing to the forward portion of the compressor housing 64 and its six cast iron strengthening/centring ribs 92.

A similar clip or clamping band 102 is fitted externally around the casing 58 to clamp the tubular casing 58 to the stator 75 of the electric motor.

The three external clips 100, 101 and 102 make assembly of the motor/compressor easier and cheaper. These three strong clips also strengthen the tubular casing 58 when it is under maximum pressure, and allow thinner material to be used for the tubular casing 58. (In operation, the interior of casing 58 is subjected to the compressor discharge gas pressure).

The inlet pipe connector 76, and the discharge valve pipe connector 78 are then fitted, being passed through apertures formed in the tubular wall of casing 58 and screwed into respective screw-threaded bores in the compressor housing 64. The inlet pipe connector 76 and the discharge valve pipe connector 78 are then welded to the casing 58. Alternatively they may be bonded to the casing 58 by an appropriate adhesive. The inlet pipe connector 84 from the desuperheater coil is likewise welded or bonded to the casing 58.

The electric motor stator winding is supplied with electric current via three insulated stator electrical leads 104 which pass through respective bores 106 passing longitudinally through the compressor housing 64 and through registering holes in the end plate 70. The three stator leads 104 are attached to respective terminals 108 before the front end-cap 88 is welded around its rim, to the tubular part of casing 58.

The electric motor is protected by an overload protection device 113 in the stator windings.

The rear end cap 90 is likewise welded to the rear end of the tubular casing.

A removable electric supply terminal cover box 110 is fitted on to end cap 88 over the exposed portions of terminals 108. The box 110 is secured by a clip or clamping band 114.

Four external anti-vibration mountings 112 may be fitted to the motor/compressor casing and the clips 100 and 102 may also be used to hold the mountings 112 in position.

Claims (20)

1. A rotary refrigeration motor/compressor in which an elastic lateral inward flexing movement of the compressor end-plate is possible sufficient to improve the compressor volumetric efficiency by automatically reducing the clearance of the compressor rotor in the chamber and thereby improving the hydrodynamic gas-sealing at both sides of the compressor rotor, as the motor/compressor casing pressure rises.

2. A rotary refrigeration motor/compressor in which an elastic lateral outward flexing movement of the compressor end-plate is possible and is utilised to control refrigerant liquid "flood-back" difficulties, when starting, by automatically increasing the clearance of the compressor rotor in its chamber under "flood-back" conditions, whereby a sudden increase in hydraulic pressure in the compressor chamber can be relieved by outward flexing of the compressor end-plate.

3. A rotary refrigeration motor/compressor in which a compressor stator/shaft-bearing/supporting rib combination is moulded and machined as one assembly, to ensure exact alignment, and includes several long supporting ribs.

4. A rotary refrigeration motor/compressor according to claim 3 wherein the compressor stator/shaftbearing/supporting rib combination is a "sliding-fit" in a motor/compressor casing.

5. A hermetic rotary motor/compressor which is designed to have a small diameter casing, so that it will easily fit into a compact appliance. The motor/compressor may be installed in the vertical or near-horizontal planes.

6. A single-staged, rotary refrigeration motor/compressor in which the extremely small elastic lateral inward flexing movement of the compressor end-plate is sufficient to improve the compressor volumetric efficiency. In the compressor of the invention its clearance volume is automatically reduced, and the hydrodynamic gas-sealing at both sides of the compressor rotor, is improved as the motor/compressor casing pressure rises. The greatest reduction in clearance volume occurs when extra compressor capacity is most needed i.e. when the motor/compressor is operating under high ambient temperature/pressure conditions.

7. A single-staged rotary refrigeration motor/compressor in which an elastic lateral outward flexing movement of the compressor end-plate is utilised to control refrigerant liquid "flood-back" difficulties, when starting. In the compressor of the invention its cylinder clearance volume is automatically increased under "f lood- back" conditions, as any sudden hydraulic pressure in the compressor cylinder is relieved by a minute amount of outward flexing of the compressor end-plate. Under "f lood- back" conditions the liquid refrigerant is forced past the compressor rotor gas sealing surfaces and it does no damage to the motor/compressor.

8. A single-staged, rotary refrigeration motor/compressor in which the compressor stator/shaftbearing/supporting rib combination is moulded and machined as one assembly, to ensure exact alignment. Several long supporting ribs are used in the invention, and the whole compressor stator/shaft-bearing/supporting rib combination is a "sliding-fit" in the hermetic motor/compressor casing.

9. A refrigeration motor/compressor including a compressor housing defining a working chamber, a member movable in said working chamber for pumping gaseous refrigerant, a driving shaft operatively connected with said movable member and rotatable in bearing means in said compressor housing to drive said movable member and means for maintaining an oil mist in the refrigerant, the arrangement being such that, in operation, oil from said oil mist can reach said bearing means for lubricating said bearing.

10. The combination of a motor/compressor according to claim 9 including an electric motor for driving the compressor, the electric motor including a stator and a rotor, said movable member of the compressor comprising a compressor rotor mounted on said shaft at one end thereof, the electric motor rotor being mounted at the other end of said shaft, with said bearing means being disposed between the motor rotor and said compressor rotor, said compressor cylindrical housing and said electric motor stator being fitted coaxially within a common casing.

11. A motor/compressor for refrigeration or airconditioning purposes, comprising a compressor housing, a compressor rotor rotatable in the compressor housing and carried by a shaft extending through the compressor housing and supported by a bearing in said compressor housing, the shaft at its end remote from the compressor rotor carrying the rotor of an electric motor positioned within an electric motor stator, said compressor housing and said electric motor stator being disposed at different axial locations within a sealed tubular casing, and each being a close fit within said casing whereby the casing serves to hold the electric motor stator and the compressor housing in axial alignment with one another.

12. A motor/compressor according to claim 11, wherein external circumferential clamping rings are secured around the casing at the location of said compressor housing and the electric motor stator to hold these components fixedly in the casing.

13. A motor/compressor for refrigeration or airconditioning purposes, which include a compressor housing received as a close fit in a cylindrical casing, said compressor housing affording a rotor chamber for the compressor rotor, at one end of the compressor housing, and which includes a portion, formed with a bearing for a rotor shaft and which portion extends away from said compressor rotor chamber for an axial distance which is substantially greater than the axial extent of said rotor chamber and preferably several times greater, and wherein the lastnoted portion includes surfaces engaging the interior surface of said cylindrical casing.

14. A refrigeration circuit or air-conditioning system including a circuit for refrigerant gas and oil and a motor/compressor in said circuit for pumping the refrigerant and oil around said circuit, wherein said circuit includes a hermetic casing containing said motor/compressor, the casing being so arranged that the exit from said casing, in said circuit, for the refrigerant, is disposed at substantially the lowermost point in said casing, to ensure that oil draining within the casing is discharged therefrom with the refrigerant gas, in operation of the circuit.

15. A refrigeration or air-conditioning system including a circuit for refrigerant gas and oil and a motor compressor in said circuit for pumping the refrigerant around said circuit, said circuit including a hermetic casing containing said motor/compressor and further including a heat exchanger remote from said casing for desuperheating the compressor discharge line gases, and wherein the oil-carrying discharge line gases are returned to said casing from the desuperheater heat exchanger for the purpose of lubricating and cooling the motor shaft bearing and cooling the electric motor windings.

16. A motor/compressor substantially as hereinbefore described with reference to and as shown in Figures 1 to 3 of the accompanying drawings.

17. A motor/compressor substantially as hereinbefore described with reference to and as shown in Figures 4 to 8 of the accompanying drawings.

18. A refrigeration or air-conditioning system substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

19. A refrigeration or air-conditioning system substantially as hereinbefore described with reference to Figures 4 to 8 of the accompanying drawings.

20. Any novel feature or combination of features described herein.