Air conditioning system having an improved internal heat exchanger

An air conditioning system having an improved internal heat exchanger (IHX) assembly. The IHX assembly includes an elongated cavity for low pressure refrigerant flow from an evaporator and an interior tube disposed within the cavity for high pressure refrigerant flow from a condenser, and a pressure equalization passage between the low and high pressure sides. The passage is large enough to allow pressures to equalize between the condenser and evaporator while the air conditioning system is inactive, so as to prevent the pressure differential that would otherwise enable the loss of refrigerant oil from the compressor, and small enough not to effect the operation of the air conditioning system. The pressure equalization passage may be a by-pass valve assembly having a reed portion that is normally open when the air conditioning system is inactive and closed when the air conditioning system is active for maximum cooling efficiency.

TECHNICAL FIELD OF INVENTION

The invention relates to an automotive air conditioning system having an improved internal heat exchanger; more particularly, to an internal heat exchanger having a passive by-pass valve between high pressure side and low pressure side for preventing oil migration throughout the air conditioning system during periods of inactivity.

BACKGROUND OF THE INVENTION

An automotive air conditioning system typically includes a condenser mounted in proximity to the front grill, a refrigerant compressor located within the engine compartment, and an evaporator contained in an HVAC housing that is essentially inside the passenger compartment. Internal heat exchangers (IHX), such as the double pipe IHX disclosed in SAE Publication No. 2007-01-1523 and the internal coiled tube IHX disclosed in U.S. patent application Ser. No. 12/487,709 are used to take advantage of the temperature differential between the refrigerant low pressure side and the refrigerant high pressure side to improve the overall cooling capacity of the air conditioning system.

The main inner volume of the compressor, the so called crankcase, is substantially hollow, but numerous moving components are either contained in or exposed to it, such as the central drive shaft and associated support bearings, swash plate, and reciprocating pistons. During operation, the compressor pumps refrigerant through the air conditioning system. The refrigerant carries entrained lubricant oil, also known as refrigerant oil to those of ordinary skill in the art, which reaches and lubricates the various moving part interfaces within the air conditioning system including the moving components within the compressor. When the compressor sits for extended periods of non-operation, it is desirable that a substantial pool of lubricant oil remain at the bottom of the crankcase to be available to lubricate the interfaces during start up.

Observations made prior to the subject invention found that lubricant oil appeared to be actively leaving the compressor crankcase during periods of vehicle and compressor inactivity and settling within the condenser and evaporator, where it would not be immediately available at compressor start up. This phenomenon of lubricant oil migration was found to be caused by a pressure imbalance between the main crankcase volume of the compressor and other components of the air conditioning system. This imbalance was creating a condition by which liquid refrigerant oil, which is miscible in the refrigerant, was subject to a combination of internal siphoning and pushing forces that pushed and pulled the liquid out of the compressor.

U.S. patent application Ser. No. 10/874,046 provides a partial solution to the undesired migration of lubricant oil migration that includes a small pressure equalization passage provided at a high point within the compressor, between the crankcase and suction chamber in the manifold. This reduces the tendency of the liquid refrigerant-oil mixture to be pulled and or pushed out of the crankcase and into the manifold, and ultimately to the condenser. However, this solution does not adequately address the migration of the liquid refrigerant-oil mixture to the evaporator.

It is desirable to have a solution to reduce the tendency of liquid refrigerant-oil mixture migration to both the condenser and evaporator. It is further desirable for a solution that requires minimal modification of existing components of an air conditioning system.

SUMMARY OF THE INVENTION

An embodiment of the invention provides for an improved internal heat exchanger (IHX) assembly for an automotive system air conditioning system, in which the IHX assembly includes a substantially cylindrical cavity for low pressure refrigerant flow (low pressure side) and an interior tube disposed within the cylindrical elongated cavity for high pressure refrigerant flow (high pressure side). The IHX assembly provides for a pressure equalization passage between the internal tube and the elongated cavity to provide for direct hydraulic communication between the low and high pressure sides. The pressure equalization passage is large enough to allow pressures to equalize between the condenser and evaporator while the air conditioning system is inactive, so as to prevent the pressure differential that would otherwise enable the loss of refrigerant oil from the compressor, and small enough not to affect the operation of the air conditioning system. In other words, the pressure equalization passage allows direct hydraulic communication between the condenser and evaporator, in which vapor refrigerant may migrate directly between the condenser and evaporator while the air conditioning system is in a state of inactivity.

In an alternative embodiment, the pressure equalization passage may be that of a by-pass valve assembly that provides hydraulic communication between the high pressures side and low pressure side of the IHX assembly when the air conditioning system is in a state of inactivity. When the air conditioning system is operating, the by-pass valve assembly closes and seals the low pressure side from the high pressure side for maximum operating efficiency of the air conditioning system.

Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of an embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.

DETAILED DESCRIPTION OF INVENTION

This invention will be further described with reference to the accompanying drawings, wherein like numerals indicate corresponding parts throughout the views.

FIG. 1shows the migration of refrigerant oil within a typical automotive air conditioning system10during extended periods when the air conditioning system10and vehicle is in a state of inactivity. Over a period of several days or longer of inactivity, the natural daily thermal cycle causes the vapor refrigerant within the air conditioning system10to migrate back and forth through the compressor12, pushing out small amounts of refrigerant-oil mixture from the compressor12and into both the condenser14and evaporator18.

During early morning hours, the condenser14is exposed to lower directed, morning sun rays, but more shielded later in the day, and is relatively light weight, so that it both cools and warms relatively rapidly. The evaporator18is located typically inside an HVAC housing that is at least partially inside the vehicle cabin, is exposed to the same greenhouse effect of solar warming, and is also capable of relatively rapid warming. The relative location and inherent characteristics of the condenser14, and evaporator18, as well as the internal structures of compressor12, were found to contribute to the previously unappreciated lubricant migration phenomenon noted above.

During the early portion of the day, the sun rays warm and vaporize the liquid refrigerant within the condenser14. Shown in solid arrows, the increase in vapor pressure forces the vapor refrigerant through the crankcase of the compressor12to the evaporator18carrying with it the refrigerant-oil mixture from the compressor. During the mid-portion of the day, when the passenger compartment is heated by the greenhouse effect, the liquid refrigerant in the evaporator vaporizes, shown in broken arrows, and pushes the refrigerant-oil mixture from the crankcase into the condenser14. Over the course of several days, this back and forth washing effect of vapor refrigerant forces the refrigerant-oil mixture out of the compressor12and into both the condenser14and evaporator18, leaving the compressor12voided of refrigerant oil. The restriction of the thermal expansion valve (TXV)16prevents vapor or liquid refrigerant from flowing directly to the evaporator18from the condenser14or vice versa when the air conditioning system is in a state of inactivity.

In accordance with a preferred embodiment of this invention, referring toFIGS. 2 through 5, is an elegant and cost efficient solution to the problem of refrigerant oil migration during prolonged periods when the air conditioning system is inactive.

Shown inFIG. 5is an automotive air conditioning system10that includes a compressor12, condenser14, a TXV16, an evaporator18, and an improved IHX assembly100hydraulically connected by a series of refrigerant tubes20. The IHX assembly100uses the relatively lower temperature and lower pressure refrigerant exiting the evaporator18to pre-cool the relatively higher temperature and higher pressure refrigerant exiting the condenser14prior to the TXV16. The flow of low pressure refrigerant from evaporator18is counter-current to the flow of high pressure refrigerant from condenser14through the IHX assembly100. An alternative embodiment (not shown) is that the flow of low pressure refrigerant is concurrent with the flow of high pressure refrigerant.

Shown inFIG. 2is a partial cut-away perspective view of one embodiment, in which the housing102of the improved IHX assembly100includes an exterior surface104, an interior surface106, a first end134, and a second end136. The interior surface106defines a substantially cylindrical cavity130disposed about Axis A. The exterior surface104of the housing102also has a substantially cylindrical shape; however, the shape of the exterior surface104of the housing102may be any shape provided that it is capable of accommodating a preferably cylindrical shaped cavity. Disposed within housing102is an internal tube108extending substantially parallel to Axis A. The internal tube108is sized to fit within the cylindrical cavity130while providing for a gap144between the internal tube108and interior surface106. The gap144provides a substantially unobstructed pathway for low pressure refrigerant flow through the cylindrical cavity130.

The internal tube108defines an aperture122providing a pressure equalization passage110between the internal tube108and the elongated cavity130. The pressure equalization passage110is large enough to allow pressures to equalize between the condenser14and evaporator18while the air conditioning system is inactive, so as to prevent the pressure differential that would otherwise enable the loss of refrigerant-oil mixture from the compressor12, and small enough not to effect the operation of the air conditioning system. In other words, the pressure equalization passage provides a significant “slow leak” of pressure, but an insignificant “fast leak.” During periods of extended inactivity, the pressure equalization passage110allows the vapor refrigerant to cycle directly from the evaporator18and condenser14, completely bypassing the compressor12. Since the refrigerant vapor does not migrate through the compressor12, the refrigerant-oil mixture is not pushed or pulled out of the crank case of the compressor12.

Another embodiment of the invention provides for a bypass valve assembly200for sealing the pressure equalization passage110or aperture122when the air conditioning system is in operation and to open the pressure equalization passage110or aperture122when the system is inactive. The bypass valve assembly200enables the aperture122to be larger than without the bypass valve assembly200; thereby, providing faster pressure equalization when the air conditioning system is inactive.

Shown inFIG. 2, the by-pass valve assembly200may include a reed portion202cooperating with the aperture122to provide a reed valve203. The reed valve203would be normally in an open position, in which the pressure equalization passage110is unobstructed when the air conditioning system is inactive. The reed portion202could be biased away from the aperture122when the pressure differential between the high pressure side in the internal tube (P2) and the low pressure side in the elongated cavity (P1) is less than 10 psig, thereby exposing the aperture122. Shown inFIG. 4, when P2is much greater than P1, P2forces the reed portion202up against and hermetically seals the aperture122to ensure there are no leaks between the high and low side for efficient air conditioning operation. Shown inFIG. 3, when the air conditioning system is inactive, P2drops significantly relative to P1. As the pressure differential is less than 10 psig, which is a good indicator of system off, the reed portion202lifts away from the aperture122; thereby, allowing the refrigerant vapor pressures between the condenser14and evaporator18to equalize and by-passes the compressor12.

The by-pass valve assembly200may also include a sleeve204having a longitudinal slit206, which allows the normal diameter (D1) of the sleeve204to be compressed and reduced to a smaller diameter (D2) before the sleeve204is inserted into the internal tube108. Once inserted, the sleeve204expands to its normal diameter (D1) to create an interference fit within the internal tube108. The sleeve204includes the reed portion202such that when the sleeve204is positioned correctly within the internal tube, the reed portion202is immediately adjacent the aperture122. Shown inFIG. 3, the reed portion202is biased apart from and unseals the aperture when the pressure differential between the high pressure refrigerant and low pressure refrigerant (P2-P1) is equal to or less than 10 psig. Shown inFIG. 4, the reed portion202is biased toward and hermetically seals the aperture122when the pressure differential between the high pressure refrigerant and low pressure refrigerant (P2-P1) is greater than 10 psig.

To ensure that the sleeve204is properly positioned within the internal tube108such that the reed portion202is immediately adjacent the aperture122, a protrusion124having a predetermined shape may be provided at a predetermined location within the interior wall126of the internal tube108and a cutout208having a complementary shape to that of the protrusion may be provided at one end of the sleeve204immediately adjacent to the protrusion, such that the cutout208locates and locks onto the protrusion124. Shown inFIG. 2, the interior wall126of the internal tube108includes a protrusion124having a semi-spherical shape and the sleeve204includes a cutout208having a complementary semi-circular shape. As the sleeve204is inserted into the internal tube (from the left toward the right) during the assembly operation, the cutout208cooperates with the protrusion124to align and limit the travel of the sleeve204within the internal tube108such that the reed portion202is properly positioned immediately adjacent the aperture122. The illustration of the semi-spherical protrusion124and corresponding complementary shaped cutout208is provided for exemplary purposes only and is not intended to be limiting. Those skilled in the art would recognize that any shapes may be utilized provided that the shapes are complementary with each and serves to align and limit the travel of the sleeve204relative to the internal tube108such that the reed portion202is properly positioned immediately adjacent the aperture122.

An advantage of the internal heat exchanger disclosed herein is that it provides a solution of mitigating refrigerant oil migration to the condenser and evaporator of an air conditioning during prolonged periods of inactivity. Another advantage is that the internal heat exchanger presents an elegant and cost effective solution without adding additional components to the air conditioning system other than a by-pass valve in the internal tube of the IHX assembly.