INTERNAL HEAT EXCHANGER ACCUMULATOR BACKGROUND OF THE INVENTION a) Field of the Invention The present invention relates to improvements of an accumulator for use in an air-conditioning or heat pump system, and more particularly to a suction accumulator suitable for use in an air-conditioning system of a motor vehicle. b) Description of the Prior Art Closed-loop refrigeration/heat pump systems conventionally employ a compressor that is meant to draw in gaseous refrigerant at relatively low pressure and discharge hot refrigerant at relatively high pressure. The hot refrigerant typically condenses into liquid as it is cooled in a condenser. A small orifice or valve divides the system into high and low-pressure sides. The refrigerant on the high-pressure side passes through the orifice or valve and turns from liquid into gas in the evaporator as it picks up heat. At low heat loads it is not desirable or possible to evaporate all the liquid. However, liquid refrigerant entering the compressor (known as"flooding") causes system efficiency loss and can cause damage to the compressor. Hence it is standard practice to include an accumulator between the evaporator and the compressor to separate and store the excess liquid. An accumulator for an automotive air-conditioner system is ; typically a metal can, welded together, and often has fittings attached for a switch and/or charge port. One or more inlet tubes and an outlet tube pierce the top, sides, or occasionally the bottom, or attach to fittings provided for that purpose.

The refrigerant flowing into a typical accumulator will impinge upon a deflector or baffle intended to reduce the likelihood of liquid inadvertently flowing out the exit.

Some prior art is concerned with reducing the turbulence of the inlet flow (US 5184480) as a way to reduce liquid carryover. Other designs are more concerned with the coupling between the inner reservoir and the outlet passage (US Patents 5660068,5179844,4627247), mainly to reduce the pressure drop across the accumulator (a critical system performance parameter).

Another feature of the prior art is the inclusion of a desiccant in the accumulator. Some refrigerant systems are more susceptible to moisture ingression and damage than others, especially less modern systems. For many systems it is necessary to remove any moisture, and the accumulator is a convenient spot to house the desiccant. Many early designs featured desiccant cartridges and the like (US Patents 4509340,4633679,4768355,4331001), but the typical modern usage is a fabric bag of some suitable shape, full of desiccant beads and secured to some inner feature of the accumulator (like the J-shaped outlet tube) where the beads will contact the liquid refrigerant.

A further feature typical of the prior art is the use of insulation placed around the outside of accumulators to modify the thermal characteristics (US 5701795). This is an added expense and is only used when required to reduce flooding.

One common feature of accumulators in typical usage is that they employ some technique to return compressor oil to circulation. Compressor oil generally circulates with the refrigerant throughout the system, but tends to accumulate in the reservoir of the accumulator. A typical method to return oil to circulation is utilizing an outlet tube for the refrigerant gas that dips low into the reservoir before exiting the accumulator. A small hole in the outlet tube at the low point will allow liquid to be entrained in the gas flow to the compressor. It is inevitable that some of this liquid will be refrigerant. This liquid refrigerant returning to the compressor reduces system efficiency.

In normal operation the gas returning to the compressor is quite cool compared to the liquid from the condenser. It is well known that the cooling capacity and efficiency of the refrigeration cycle can be increased if the returning gas is used to further cool the condensate before it reaches the expansion device (US5075967). (In transcritical applications liquid only exists at lower pressures, after the expansion device. Strictly speaking, the condenser is a"gas cooler".

However we will use the terms"condenser"and"condensate"with the understanding that the principles of our invention apply to transcritical refrigerant systems as well.) A heat exchanger that is used to transfer heat from the high- pressure side to the low-pressure side is referred to as a"suction-line heat

exchanger" (SLHX) or an"internal heat exchanger" (IHX). ("lnternal"to the system, as compared to the condenser and evaporator that exchange heat between the system and the environment). In systems that use an accumulator with an oil pick-up hole, IHX the effect can be enhanced as the liquid refrigerant entrained by the oil pick-up hole is evaporated to cool the condensate. Prior art recognizes that a conventional heat exchanger can be used as an IHX (US5562157, US5609036, US5687419), but generally mobile applications do not have room for a larger evaporator and cannot economically justify another component. Combining the IHX with the accumulator can provide a cost-effective solution that requires only incrementally more space and weight.

Several examples of prior art suggest that a coil or section of tube containing hot condensate can be located within the reservoir section of the accumulator for heat exchange (US5075967, US5245833, US5622055), however such designs are not optimal. The hot condensate will boil the low-pressure liquid in the accumulator reservoir, defeating the purpose of the reservoir and reducing system efficiency by loading the system with gas. There is prior art that suggests the coil of hot condensate can be outside the main reservoir (US6298687), however that art attempts to enhance the heat exchange with the reservoir. Our study clearly shows that the heat transfer to the reservoir must be reduced.

Further, the prior art shows IHX accumulators that will not work well as accumulators in other ways. For instance, US6298687 shows an oil pickup hole arranged so that the reservoir will drain away to the compressor when the system is shut off. There is also no technique to reduce the turbulence on gas entry, or prevent the liquid in the reservoir from escaping to the gas exit. Much of the prior art is also difficult to assemble. US6298687 shows the inlet and exit of the high- pressure line on opposite ends of the accumulator, which is not easily amenable to mass manufacturing. There is a requirement for an internal heat exchanger combined with an accumulator, with controlled heat transfer from the high pressure line to the reservoir, in a simple, cost and space effective configuration that is easily manufactured and preserves the accumulator function.

SUMMARY OF THE INVENTION

In our International PCT Application No. PCT/CA01/00083 filed January 25th, 2001 we have disclosed a suction accumulator of advanced design which includes a number of important improvements rendering it particularly suitable for use in vehicle air-conditioning systems.

The present invention provides a still further improved suction accumulator.

More specifically, the invention provides an accumulator for use in an air-conditioning or heat pump system comprising: a hermetically sealed outer housing comprising a top, an inlet opening, an outlet opening, a peripheral side wall, and a base; an inner liner positioned within said outer housing, said inner liner having a peripheral wall and a base which form a container to receive refrigerant delivered through said inlet opening and separate said refrigerant into liquid and vapour, said inner liner being spaced from the peripheral wall of said outer housing to define therewith an annular passage; a heat exchange tube positioned in an angular passage, said tube designed and configured to effect transfer of heat within said system from high pressure refrigerant to low pressure refrigerant at a controlled rate, said tube having inlet and outlet ends that extend exteriorly of said outer housing, heat insulating material separating said heat- exchange tube from the interior container to inhibit transfer of heat to refrigerant within said inner container; transfer passages at respective upper and lower ends of said annular passage, one said transfer passage comprising an inlet, communicating said annular passage to the interior of the inner liner, and the other said transfer passage comprising an outlet communicating said annular passage to the exterior of said housing via said outlet opening; the arrangement being such that vaporized refrigerant drawn from said inner liner enters said annular passage through said one transfer passage while liquid refrigerant is prevented from entering, said vaporized refrigerant flowing through said annular passage and along said heat exchange tube to said other transfer passage from where it exits said accumulator via said outlet opening.

The heat exchange tube provides a way of incorporating in the accumulator a mechanism for heat exchange between the high pressure side of the system, i. e. between the outlet of the compressor, the condenser and the

expander valve, and the low pressure side of the system. As such the tube can embody various enhancements such as those designed to increase surface area.

Further, although the preferred embodiment has a single, continuous heat exchange tube other configurations are possible. Effective heat exchange is accomplished by circulating the relatively hot refrigerant from the high pressure side through the heat exchange tube while passing over this heat exchange tube the gaseous refrigerant leaving the accumulator and being delivered to the inlet of the compressor. This both pre-cools the liquid refrigerant prior to expansion, increasing the system cooling capacity, and helps to ensure that the refrigerant gas flow reaching the compressor does not contain any liquid refrigerant. The effective heat exchange is accomplished with minimal increase in suction line pressure loss and without compromising the accumulator function. The heat exchanger disclosed herein has few additional parts, is more effective, and in its preferred embodiments is easier and cheaper to manufacture than accumulator and internal heat exchanger combinations as known in the prior art.

Preferably the heat exchange tube is arranged in the form of a helical coil in the annular passage between the outer housing and the inner liner of the accumulator, so as to define in that annular passage a helical flow path for the refrigerant vapor along the length of the coil. The outer diameter of the heat exchange tube is matched to the width of the annular passage between the outer housing and the inner liner providing a seal so that virtually all of the refrigerant gas flow travels the full length of the helical path. If a single helical coil is used with a return line to put the inlet and outlet on the same end of the outer housing then the refrigerant gas must be prevented from using the shorter path thus formed to bypass the helical path. The use of a double helical coil eliminates that concern.

The inner liner is preferably fabricated in a plastic material of poor heat conductivity so that the liquid refrigerant contained therein is insulated from the heat of the coil and of the outer housing.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will further be described, by way of example only, with reference to the accompanying drawings wherein:

Figure 1 is a schematic circuit diagram of an air-conditioning system (which may be used for cooling or for heating) embodying a presently preferred embodiment of the accumulator in accordance with the present invention; Figure 2 is a somewhat schematic sectioned perspective view of the accumulator of the air-conditioning system shown in Figure 1; Figure 3 is a sectional view to a larger scale taken approximately on the line III-III in Figure 2; Figure 4 is an exploded view corresponding to Figure 2 showing the parts of the accumulator separated; Figures 5 and 6 show enlarged views of portions of Figure 2 to illustrate the flow of refrigerant gas; Figure 7 is a somewhat schematic longitudinal sectional view showing an alternative embodiment of the accumulator of the present invention; and Figure 7A is a fragmentary schematic perspective view showing an upper portion of the accumulator of Figure 7; Figure 8 is a longitudinal sectional view of a further possible accumulator configuration in accordance with the present invention.

Figure 9 is a longitudinal section view of another further possible accumulator configuration in accordance with the present invention.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS The circuit diagram of Figure 1 shows a schematic closed circuit air- conditioning system that may be used as a cooling unit or as a heat pump.

Refrigerant fluid is stored in liquid form in an accumulator 10 to be drawn therefrom in gaseous form to the inlet of a compressor 12. The compressor delivers hot high-pressure refrigerant gas to a condenser 14 where the gas is cooled and typically partially converted to a liquid form. Refrigerant fluid from the condenser (still under high pressure) is expanded to a lower pressure through an

expander valve 16, thereby undergoing a rapid drop in temperature, the low pressure cold fluid being heated in an evaporator 18 from where it is returned to the accumulator 10 in a mixed flow of liquid and gas. Depending upon the loading of the system, more or less of the refrigerant fluid is condensed and evaporated, refrigerant that is in excess of the instantaneous requirements of the system being stored in liquid form in the accumulator 10. As thus far described, the circuit shown in Figure 1 is conventional.

The system of Figure 1 is modified by directing the partially cooled but still warm refrigerant fluid delivered from the condenser through a heat exchange coil 20 in the accumulator. As is more fully described hereinafter, the heat exchange coil 20 is not in contact with the refrigerant liquid in the accumulator 10, but rather is positioned to be contacted by refrigerant gas that is withdrawn from the accumulator by the compressor 12, and its purpose to pre-cool the high-pressure refrigerant and to ensure complete vaporization of the refrigerant delivered to the compressor.

The structure of accumulator 10 is more clearly shown in Figures 2 to 6 and comprises a cylindrical outer container 22 the lower end of which is closed by a bottom cap 24 and the upper end of which is attached and hermetically sealed to a disc-shaped head fitting 26 which includes a plurality of ports to receive the following connections: an inlet tube 28 to deliver refrigerant fluid from the evaporator; an outlet tube 30 through which refrigerant gas is passed from the accumulator to the compressor 12; an inlet connection 32 and an outlet connection 34 communicating with the heat exchange coil 20 for delivering therethrough the refrigerant fluid passing from the condenser 14 to the expander valve 16.

Within the outer container is a c-axially arranged cylindrical inner liner 36 the upper end of which is positioned closely against the underside of the head fitting 26 but which defines therewith transfer passages 38, one of which is seen in Figure 2. A series of transfer passages 38 are arranged at spaced intervals around the periphery of the head fitting. Ribs between the passages 38

rest upon the upper end of the inner liner 36. As seen in Figure 3, there is an annular passage 40 extending from top to bottom between the inner liner 36 and the outer container 22. A continuation of this passage extends radially inwardly on the underside of the inner liner 36 which is spaced from the bottom cap 24 by projecting ribs 42. A central tube 44 which communicates with the annular passage 40 at the lower end of the accumulator extends centrally upwardly therein and is connected with the outlet tube 30, both being hermetically sealed to the head fitting 26.

The inlet connection 32 for the heat exchanger coil 20 extends vertically to near the bottom of the accumulator, as best seen in Figure 2, the coil then extending helically upward in the annular space 40, the upper end of the coil turning vertically to merge with the outlet connection 34. To accommodate the vertical arrangement of the connections 32 and 34, the inner liner is formed with axially extending recesses 46,48 (Figure 3) in its outer surface. In these recesses, the connections 32,34 are accommodated in such a way that they do not project beyond the cylindrical envelope defined by the outer surface of the inner container. The inner container 36 and the inlet and outlet connections 32, 34 are surrounded by a closely fitting outer liner 50 which defines the inner cylindrical surface of the annular passage 40. This annular passage is of constant radial width that corresponds closely to the outside diameter of the tubing forming the heat exchanger coil 20 so that the latter fits snugly between the outer liner 50 and the outer container 22, this snug fit achieving a seal between the coil and these components to prevent refrigerant gas from bypassing the extended flow path defined between turns of the coil. As will be evident from Figures 2,5 and 6, the outer liner 50 extends from the upper edge of the inner liner 36 over the major portion of the length of the latter, terminating slightly above the location of the lower end of the coil 20.

IN OPERATION Refrigerant fluid at low pressure is delivered from the evaporator through the inlet tube 28 into the inner liner 36 where it separates, the liquid fraction thereof gathering at the lower end of the inner liner together with a minor

quantity of entrained oil that is typically included to provide lubrication for the compressor.

As determined by the demand of the heating or cooling load, the compressor 12 is driven to draw gaseous refrigerant from the accumulator.

Suction applied by the compressor communicates through the central tube 24, the annular space 40, and the transfer passages 38 with the interior of the inner liner 36. Thus refrigerant gas from this region is drawn through the transfer passages 38 into the annular passage 40. According to the suction demands of the compressor the low pressure created in the accumulator causes more or less of the liquid refrigerant to evaporate. However the refrigerant gas cannot pass directly to the lower end of the annular passage, but rather is channelled by the coil 20 to descend in a helical path between the turns of the coil and in heat exchange relation thereto until it reaches the lower end of the accumulator from whence it can pass radially inwardly between the projecting ribs 42. During this descent the refrigerant gas picks up heat from the coil 20 thus ensuring that the refrigerant delivered to the compressor is completely vaporized. This is achieved without excessively heating the liquid refrigerant within the lower end of the inner liner 36 by virtue of the fact that the latter is made of a poorly heat-conducting plastic, and further by the presence of the outer liner 50 which may also be of a similar heat insulating material. The conductivity of the material of the inner liner 36 and of the outer liner 50 is no more than about 10 watts/m. K. It will be noted that refrigerant gas in the passage 40 cannot move directly to the bottom of the passage through the recesses 46,48 formed in the inner liner, since these are effectively blocked off by the outer liner 50.

As described in our above referenced International PCT application, the inner liner 36 will typically include a desiccant mass (not shown) to extract any moisture that may be present in the refrigerant fluid. Furthermore as also described in that application the lower ends of the inner container 36 may contain a filter and a bleed hole through which oil gathering there can be drawn into the refrigerant gas as it moves across the underside of the inner liner 36.

It will be observed that the refrigerant gas leaving the accumulator through the passage 40 flows in counter-current relationship to the warm

refrigerant fluid moving through the coil 20 and thus the refrigerant gas passes the warmest region of the coil immediately before it flows beneath the lower end of the inner liner into the central tube 44. This arrangement enhances the effect of the heat transfer.

It is conventional in accumulators particularly accumulators for use in automotive air-conditioning systems, to provide for a baffle means to prevent liquid refrigerant that enters the accumulator through the inlet pipe 20 from passing directly to the outlet passage, and any of the various means known in the prior art can be provided for this purpose. The design of the accumulator shown in Figures 2 to 6 provides a baffle effect by the configuration of the underside of the head fitting 26. The inner end of the inlet tube 28 on the underside of the head fitting 26 is surrounded by a recessed groove which prevents any tendency for liquid refrigerant clinging to the edge of the tube 28 from travelling across the under surface of the head fitting 26. Additionally, the transfer passage 38 spaced around the upper end of the inner liner 36 are in fact offset slightly above the level of the lower surface of the head fitting 26. Additionally, the detailed shape of these labyrinth transfer passages 38 can also be arranged to cause turbulence in the gas flowing into heat exchange passage, enhancing heat exchange with the coil 20.

Although the accumulator of Figures 2 to 6 shows all of the fluid connections extending through the head fitting 26, other arrangements are possible, for example as shown in Figure 7 where the accumulator 110 has only the inlet tube 128 delivering refrigerants from the evaporator and the outlet tube 130 delivering refrigerant gas from the accumulator to the compressor are arranged in the head fitting 126. In this embodiment the heat exchanger coil 120 as before extends helically in closely fitting relationship in the passage 140 between the outer container 122 and the inner liner 136. However in this embodiment the coil 120 is a double helix so that both its inlet connection 132 and outlet connection 134 pass through the bottom cap 124 of the accumulator. Thus in alternate turns of the coil 120 the refrigerant fluid flows in opposite directions. In this embodiment therefore the outer surface of the inner liner 136 can be perfectly cylindrical and therefore there is no requirement for an outer liner such as that shown at 50 in Figures 2 to 6. The embodiment of Figure 7 also demonstrates

one method for incorporating a deflector into the accumulator, shown in more detail in Figure 7A. The deflector 150 is saddle-shaped, having a diametral crest 150.1 from which extend two downwardly sloping half circular flanks 150.2. A central circular hole 150.3 in the crest surrounds the upper end of the central tube 144 of the inner liner 136 and is sized to seal around a short tubular socket 150. 4 on the underside of the head fitting 126. The deflector 150 can be made from a sheet metal disk having a diameter corresponding to the internal diameter of the inner liner 36, and thus abuts the inner liner at opposite ends of the crest 150. 1 and in regions adjacent thereto, the lower sides of the flanks 150.2 being separated from the inner wall of the liner 136 by crescent shaped passages 150.5.

On the underside of the deflector 150 spaced from the inlet tube 128 a transfer passage 138 communicates the interior of the inner liner 136 with the annular passage 140. The upper side of this passage 138 is of wide angled inverted V shape and is blocked by the peripheral edge of the deflector 150 so that there is no communication into the passage 138 from the upper side of the deflector. In operation, the refrigerant gas and liquid from the evaporator delivered into the accumulator through the inlet tube 128 will impinge upon the crest 150.1 to one side of the socket 150.4 and flow into the reservoir section through the opening 150.5. Refrigerant gas exiting from the reservoir section of the accumulator will be drawn through the transfer opening 138 to enter the heat exchange section provided by the annular passage 140 and thereafter will exit the accumulator through the central tube 144 and the outlet tube 130.

A still further possible configuration is shown in Figure 8. Here the inlet tube 228 opens centrally into the upper end of the outer container 222, which has an integral top surface. However in this embodiment the cylindrical inner liner 236 has an upwardly extending central tube 244 that is closed at its upper end, apart from a small anti-siphon hole 245. The outlet for gas delivered from the accumulator to the compressor is formed in the bottom cap 224, this outlet 230 communicating with a vertically extending tube 231 that terminates near the closed upper end of the tube 244. In this embodiment the heat exchange tube 220 as before is arranged in any convenient manner in the annular passage 240 between the outer container 222 and the inner liner 236. As shown in Figure 8 the inlet 232 and the outlet 234 of the heat exchange coil 220 pass through the side wall of the outer container 222, although other configurations are possible.

Figure 9 shows still another possible embodiment. In this case the refrigerant gas and liquid from the evaporator enter through the inlet tube 328 in the side wall of the accumulator 310. The liquid impinges upon the (optional) deflector 340 and flows into the reservoir section. Under impetus from the compressor, the gas flows into the open end of the riser tube 331 of the liner 336.

It then flows downward through the space allowed between the liner and the bottom cap 324 and upwards through the heat exchanger passage 340. The gas collects in the cavity 338 at the top of the heat exchanger coil and exits the accumulator through the fitting 330 in the side wall. It is important that the inlet tube fit closely to the wall of the reservoir section, to avoid forming a path for fluid within the reservoir to bypass the heat exchanger passage.

Within the ambient of the invention significant changes can be made in the dimensions, shapes, sizes, orientations and materials to meet the specific requirements of the air-conditioning system that is being designed. Likewise the external structure such as the head fitting, the outer container, the position and arrangement of inlet and outlet ports can be modified as desired as can the type and arrangement of the desiccant container, oil bleed regulator and filter.

It should be understood that while for clarity certain features of the invention are described in the context of separate embodiments, these features may also be provided in combination in a single embodiment. Furthermore, various features of the invention which for brevity are described in the context of a single embodiment may also be provided separately or in any suitable sub- combination in other embodiments.

Moreover, although particular embodiments of the invention have been described and illustrated herein, it will be recognized that modifications and variations may readily occur to those skilled in the art, and consequently it is intended that the claims appended hereto be interpreted to cover all such modifications and equivalents.