Refrigeration Cycle

Abstract

Provided is a refrigeration cycle wherein a compressor, a condenser, a depressurizing/expanding means and an evaporator are provided. The refrigeration cycle uses R1234 as a refrigerant, and has an oil separating means, which forcibly separates the refrigerant and oil one from the other, in a two-phase separation region wherein the refrigerant and the oil exist in a separated state without being dissolved with each other. The refrigerant and the oil can be forcibly separated suitably at a suitable position even when the refrigerant is changed to the new refrigerant R1234yf, and the refrigeration cycle can be operated at a high efficiency as a whole.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a refrigeration cycle, and specifically relates to a refrigeration cycle which can be operated at a high efficiency as separating refrigerant and oil suitably for a case using a new refrigerant.

BACKGROUND ART OF THE INVENTION

A refrigeration cycle as used in an automotive air conditioning system, has a basic configuration as shown in FIG. 7. In FIG. 7, refrigeration cycle 101 has compressor 102 compressing refrigerant, condenser 103 condensing compressed refrigerant, expansion valve 104 as a depressurizing/expanding means for depressurizing and expanding condensed refrigerant and evaporator 105 evaporating depressurized and expanded refrigerant. The refrigerant is circulated in refrigeration cycle 101 as changing its state. In such refrigeration cycle 101, the refrigerant sometimes contains lubricating oil, such as an oil made from PAG [polyalkylene glycol], so as to enhance durability of compressor 102, for example. When using refrigerant and oil, known is a method that the oil, which has been separated from refrigerant by an oil separator provided at an appropriate position, is returned to a compressor which requires to be lubricated, without being brought into a heat exchanger as far as possible, so that a heat transfer obstruction derived from an oil adhesion in a heat exchanger, such as evaporator 105, in the cycle is suppressed. Actually, the oil separator is not provided in most cases because the refrigerant R134a, which is a typical refrigerant at present, has a good compatibility with PAG oil.

For the R134a, etc., as a conventional typical refrigerant, research and development for a new refrigerant is being performed as disclosed in Non-patent document 1, aiming at further improvement of the global warming potential (GWP), etc. R1234yf has been recently announced as the new refrigerant aiming such an improvement. And the research and development can be performed even for the application to a refrigeration cycle used in an automotive air conditioning system, etc.

PRIOR ART DOCUMENTS

Non-Patent Document

• Non-patent document 1: Refrigeration, Vol. 83, No. 965, March issue, 2008

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, because the new refrigerant R1234yf is less compatible with the PAG oil than R134a, a trouble that liquid refrigerant and oil are separated at high-pressure side in the refrigeration cycle might be caused. In other words, in a case where the new refrigerant R1234yf is used in the refrigeration cycle as shown in FIG. 7, caused might be a trouble that the R1234yf is compatible with PAG oil at low-temperature and low-pressure side (COMPATIBLE REGION) while the refrigerant and the oil tend to be separated at high-temperature and low-pressure side (TWO-PHASE SEPARATION REGION), as seen from an example of the operating condition for comparatively high load shown in FIG. 6. Once the oil is separated from the refrigerant in the middle of a refrigerant circulation route, the oil sometimes does not return to the compressor and loses the confidence of the compressor durability.

In addition, because an automotive air conditioning system with R134a refrigerant is usually provided with a sight glass, through which the refrigerant behavior can be monitored, in a liquid line of the refrigeration cycle, excess and deficiency of the refrigerant can be detected. However, in a case where the new refrigerant R1234yf is used, the above-mentioned trouble that the liquid refrigerant and the oil are separated in the middle of the refrigerant circulation route might be caused, and once the sight glass mists or is stained with the separated oil, the excess and deficiency of the refrigerant cannot be detected with the sight glass in most cases.

Accordingly, focusing on the above-described troubles in a case where the new refrigerant R1234yf is used, an object of the present invention is to make a refrigeration cycle capable of being operated at a high efficiency as a whole, as properly separating the refrigerant and the oil by compulsion at a proper position even when the refrigerant is replaced by the new refrigerant R1234yf, as preferentially returning the separated oil to a site such as a compressor which requires to be lubricated, without possibly supplying the oil to a heat exchanger, etc., which should not be supplied with an oil.

Further, another object of the present invention is to make a refrigeration cycle capable of properly detecting the excess and deficiency of the refrigerant through a sight glass which is provided in a liquid line of the refrigeration cycle even in a case where the new refrigerant R1234yf is used.

Means for Solving the Problems

To achieve the above-described object, a refrigeration cycle according to the present invention is a refrigeration cycle having a compressor for compressing refrigerant, a condenser for condensing compressed refrigerant, a depressurizing/expanding means for depressurizing and expanding condensed refrigerant, and an evaporator for evaporating depressurized and expanded refrigerant in this order in a refrigerant flowing direction, characterized in that R1234yf is used as the refrigerant, and an oil separating means for forcibly separating the refrigerant and oil one from the other is provided in a two-phase separation region, in which the refrigerant and the oil exist in a separate state without being dissolved with each other, present in a route from an exit side of the compressor to the depressurizing/expanding means. The condenser in the present invention conceptually includes a so-called “subcool condenser” which has a subcooled region where the refrigerant is condensed into a subcooled liquid refrigerant in a condenser, in addition to a normal condenser.

Namely, an oil separator is not necessary to be provided in most cases where R134a is used as a refrigerant, however, in the present invention where the new refrigerant R1234yf is used, an oil separating means is provided in a certain region, which means the above-described two-phase separation region, in a refrigeration cycle so as to separate the refrigerant and the oil by compulsion. The two-phase separation region is suitable as a place to separate the oil. The two-phase separation region is, in other words, a region where the refrigerant and the oil are being separated without special operation. The present invention uses this region as an underhanded way. As described above, the oil should not go through the heat exchanger as far as possible. However in a case where the refrigerant is in a gaseous state, the gaseous state region at an inlet side of the condenser is affected by the oil as well though even a conventional refrigerant is slightly compatible with the oil. Therefore in the present invention, it is preferable that the oil is separated in the two-phase separation region, especially at a position between the condenser and the depressurizing/expanding means (from the outlet of the gaseous region in the condenser to the inlet of the depressurizing/expanding means), and in this region the oil separating means is further preferably provided. By separating the refrigerant and the oil properly by compulsion in the two-phase separation region with various methods described later, the separated oil, without passing through a heat exchanger at a downstream side, can be returned to the compressor, etc., which requires to be lubricated. Consequently, the fear to cause a heat transfer obstruction derived from the oil adhesion in the heat exchanger can be reduced so that the refrigeration ability and the coefficient of performance of the refrigeration cycle can be improved, and additionally, the lubrication in the compressor, etc., can be always performed in a good condition, so as to get rid of the fear as to the durability.

In order to return the oil to the compressor, an oil return line for returning oil separated by the oil separating means to the compressor may be provided between the oil separating means and the compressor. For performing the oil return, a capillary tube can be connected to a crankcase of the compressor and the oil can be returned directly.

If a sight glass is provided at a certain position in a liquid line at downstream side of the oil separating means in a refrigerant circulation direction, because most oil has already been separated and removed from the refrigerant passing through the site where the sight glass is installed, the oil, which has existed together with the refrigerant in a state separated from the refrigerant, can be prevented from making the sight glass mist, so that the refrigerant behavior can be clearly monitored through the sight glass and the excess and deficiency of the refrigerant can be properly detected by the monitoring.

As described above, PAG oil made from polyalkylene glycol can be used as the oil. In the two-phase separation region where the oil separating means is provided, and specifically in a region from the condenser outlet to the decompression/expansion means inlet, the refrigerant is usually in a liquid state, and its specific gravity of the refrigerant R1234yf is less than that of PAG oil, as shown in Table 1. In other words, the oil forms a layer below the refrigerant when separated by compulsion. Therefore, if the separated oil is flowed out from the lower side in a vertical direction and if the oil separating means is disposed at a position higher than the compressor in a vertical direction, the separated oil can be easily returned to the compressor. Such a vertical position relation between the oil separating means and the compressor is effective in a case where the specific gravity of the oil is greater than the specific gravity of the refrigerant R1234yf, and is specifically effective when the oil is PAG oil.

TABLE 1
Specific gravity
R1234yf 0.97
R134a   1.08
PAG     1.00

The oil separating means itself can have various configurations. For example, it is possible that the oil separating means has a centrifugal separation means for separating the refrigerant and the oil by centrifuging the refrigerant and the oil, that the oil separating means has a collision separation means for separating the refrigerant and the oil by a collision of the refrigerant and the oil, or that the oil separating means has a trap separation means for separating the refrigerant and the oil by trapping the oil from the refrigerant and the oil.

Further, it can have a combination of the above-described configurations. For example, it is possible that the oil separating means has a centrifugal separation means for separating the refrigerant and the oil by centrifuging the refrigerant and the oil and a trap separation means for separating the refrigerant and the oil by trapping the oil from the refrigerant and the oil or that the oil separating means has a collision separation means for separating the refrigerant and the oil by a collision of the refrigerant and the oil and a trap separation means for separating the refrigerant and the oil by trapping the oil from the refrigerant and the oil.

In particular, if the trap separation means is provided at the lowest position of the oil separator and the oil is trapped at the position of the trap separation means, the separated oil can be prevented from flowing into a liquid refrigerant lifting tube, etc., which is located above.

Also, it is preferable that a temporary storage section for separated oil is provided at a lower position in a vertical direction in the oil separating means. When such a temporary storage section is provided, because the separated oil is returned to a desirable destination from a temporary storing condition where a certain amount of the separated oil is stored, a stable oil return can be performed and the oil return line can be sealed by the oil in the temporary storage section, so that the refrigerant can be prevented from undesirably flowing into the oil return line.

Also, it is preferable that an exit for separated oil is provided at a lower end in a vertical direction of the oil separating means. Such a position of the exit for the oil is effective specifically in a case where the specific gravity of the oil and the specific gravity of the refrigerant R1234yf have the same magnitude relation as described before.

The refrigeration cycle according to the present invention is basically applicable to any refrigeration cycle where the new refrigerant R1234yf may be used, and is suitable as a refrigeration cycle in an automotive air conditioning system which requires to be operated at high efficiency and to have long-term high durability of the compressor, etc.

Effect According to the Invention

The refrigeration cycle according to the present invention makes it possible to improve the durability and the reliability of the compressor in a refrigeration cycle using the new refrigerant R1234yf. Further, basically the oil is not circulated through the oil separating means providing section in the refrigeration cycle, so that the fear to cause a heat transfer obstruction by the oil adhesion in a downstream heat exchanger is reduced, so as to improve the refrigeration ability and the coefficient of performance of the refrigeration cycle. Furthermore, the behavior of the refrigerant can be surely monitored by a sight glass provided in the liquid line, so as to surely detect the excess and deficiency of the refrigerant thereby.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a systematic equipment diagram of a refrigeration cycle according to an embodiment of the present invention.

FIG. 2 is a schematic framework showing an example of an oil separating means in the present invention.

FIG. 3 is a schematic framework showing another example of an oil separating means in the present invention.

FIG. 4 is a schematic framework showing yet another example of an oil separating means in the present invention.

FIG. 5 is a schematic framework showing yet another example of an oil separating means in the present invention.

FIG. 6 is a characteristic diagram showing an example of phase state for the new refrigerant R1234yf.

FIG. 7 is a systematic equipment diagram of a conventional refrigeration cycle.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, desirable embodiments of the present invention will be explained as referring to figures.

FIG. 1 shows an equipment layout of a refrigeration cycle according to an embodiment of the present invention. As shown in the figure, up-and-down direction means the vertical direction X. Therefore, the top side in the figure means the highest position in the vertical direction, while the bottom side in the figure means the lowest position in the vertical direction. Refrigeration cycle 1 has compressor 2 compressing refrigerant, condenser 3 condensing compressed refrigerant, expansion valve 4 as a depressurizing/expanding means depressurizing and expanding condensed refrigerant and evaporator 5 evaporating depressurized and expanded refrigerant in this order in the refrigerant flowing direction (in the arrow direction), like the basic configuration shown in FIG. 7, wherein R1234yf is used as a refrigerant and oil separator 6 as an oil separating means which separates the refrigerant and the oil by compulsion is provided in a two-phase separation region, such as the two-phase separation region shown in FIG. 6, where the refrigerant and the oil exist separately without being dissolved with each other in a region from the outlet side of compressor 2 to the inlet of expansion valve 4. In this embodiment, oil separator 6 is provided between condenser 3 and expansion valve 4 in the two-phase separation region. Oil separator 6 and compressor 2 are connected to each other with oil return line 7 which returns the oil forcibly separated by oil separator 6 to compressor 2. A capillary tube can be used for oil return line 7, and one end of the capillary tube can be connected directly to the crankcase of compressor 2, etc., so as to return the oil directly to the crankcase. The above-mentioned PAG oil can be used as the oil, for example.

The position relation in the vertical direction between oil separator 6 and compressor 2, is such that oil separator 6 is disposed higher than compressor 2, which means that compressor 2 is lower than oil separator 6, so that the oil separated by oil separator 6 can be smoothly returned to compressor 2 under its own weight.

The site from oil separator 6 to expansion valve 4 in the refrigeration cycle usually becomes a liquid line, and at a certain position in the liquid line sight glass 8, through which internal behavior of the refrigerant can be observed, is provided.

Because the oil forcibly separated by oil separator 6 is returned to compressor 2 through oil return line 7, lubrication state of compressor 2 is kept in a state good enough, and the durability for a long term can be ensured. Further, because the oil forcibly separated by oil separator 6 is not supplied into downstream side of oil separator 6 in the refrigeration cycle route, the fear to cause a heat transfer obstruction by the oil adhesion in a heat exchanger, such as evaporator 5 in the shown example, which is located at downstream side can be reduced, and the refrigeration ability and the coefficient of performance of refrigeration cycle 1 can be improved. Furthermore, because the oil forcibly separated by oil separator 6 is not supplied to sight glass 8 provided in the liquid line, sight glass 8 is prevented from misting by the oil, so that the internal behavior of the refrigerant can be surely monitored so as to surely detect the excess and deficiency of the refrigerant through the monitoring of the refrigerant behavior.

Oil separator 6 can be configured into various kinds of structures. FIG. 2-FIG. 4 show structural examples where an oil separator is provided between compressor 2 and condenser 3 in the above-mentioned two-phase separation region. FIG. 5 shows a desirable structural example where oil separator 6 is provided at the most desirable position shown in FIG. 1. Some of these structural examples can be combined with each other as described above, because they are no more than examples.

In the example shown in FIG. 2, the refrigerant and the oil delivered from compressor 2 are centrifuged by pipe-shaped centrifugal separation section 11 provided as a centrifugal separation means in oil separator 6a, so as to be forcibly separated into refrigerant phase 12 and oil phase 13 which is temporarily stored in a temporary storage section for the oil at the bottom side, and the separated oil is returned through oil return line 7 to compressor 2 while the separated refrigerant is delivered to condenser 3.

In the example shown in FIG. 3, the refrigerant and the oil delivered from compressor 2 are forcibly separated into refrigerant phase 22 and oil phase 23 which is temporarily stored in a temporary storage section for the oil at the bottom side by collision separation section 21 as a collision separation means, which is provided in oil separator 6b and separates the refrigerant and the oil by the colliding between the refrigerant and the oil, so that the separated oil is returned through oil return line 7 to compressor 2 while the separated refrigerant is delivered to condenser 3.

In the example shown in FIG. 4, the refrigerant and the oil delivered from compressor 2 are forcibly separated into refrigerant phase 32 and oil phase 33 which is temporarily stored in a temporary storage section for the oil at the bottom side by trap separation section 31 as a trap separation means, which is provided in oil separator 6c and separates the refrigerant and the oil by trapping the oil from the refrigerant and the oil, so that the separated oil is returned through oil return line 7 to compressor 2 while the separated refrigerant is delivered to condenser 3.

In the example shown in FIG. 5, the refrigerant and the oil delivered from condenser 3 are centrifuged by pipe-shaped combined centrifugal separation section and lifting tube 41 provided as a centrifugal separation means in oil separator 6d, which corresponds to oil separator 6 shown in FIG. 1, so as to be forcibly separated into liquid refrigerant phase 42 and oil phase which is temporarily stored in a temporary storage section for the oil at the bottom side, and further the oil is trapped and retained by oil trap separation section 44 provided in the temporary storage section for the oil from the refrigerant lifted by combined centrifugal separation section and lifting tube 41, so that the refrigerant and the oil are forcibly separated as preventing the oil from flowing out together with the refrigerant flow. While the separated oil is returned through oil return line 7 to compressor 2, the separated refrigerant is delivered to expansion valve 4 or to the subcooled region (liquid refrigerant) in condenser 3 where condenser 3 is the above-described subcool condenser.

Thus the oil separation means itself can be configured in various structures, as depending on a place to provide in the two-phase separation region.

INDUSTRIAL APPLICATIONS OF THE INVENTION

The refrigeration cycle according to the present invention is applicable to any refrigeration cycle where the new refrigerant R1234yf may be used, and is suitable for a refrigeration cycle used in an automotive air conditioning system.

EXPLANATION OF SYMBOLS

• 1: refrigeration cycle
• 2: compressor
• 3: condenser
• 4: expansion valve as decompression/expansion means
• 5: evaporator
• 6, 6a, 6b, 6c, 6d: oil separator as oil separating means
• 7: oil return line
• 8: sight glass
• 11: centrifugal separation section as centrifugal separation means
• 12, 22, 32: refrigerant phase
• 13, 23, 33, 43: oil phase
• 21: collision separation section as collision separation means
• 31: trap separation section as trap separation means
• 41: combined centrifugal separation section and lifting tube
• 44: oil trap separation section

Claims

1. A refrigeration cycle having a compressor for compressing refrigerant, a condenser for condensing compressed refrigerant, a depressurizing/expanding means for depressurizing and expanding condensed refrigerant, and an evaporator for evaporating depressurized and expanded refrigerant in this order in a refrigerant flowing direction, characterized in that R1234yf is used as said refrigerant, and an oil separating means for forcibly separating said refrigerant and oil one from the other is provided in a two-phase separation region, in which said refrigerant and said oil exist in a separate state without being dissolved with each other, present in a route from an exit side of said compressor to said depressurizing/expanding means.

2. The refrigeration cycle according to claim 1, wherein said oil separating means is provided at a position between said condenser and said depressurizing/expanding means.

3. The refrigeration cycle according to claim 1, wherein an oil return line for returning oil separated by said oil separating means to said compressor is provided between said oil separating means and said compressor.

4. The refrigeration cycle according to claim 1, wherein a sight glass capable of monitoring behavior of said refrigerant present inside is provided at a downstream side of said oil separating means as viewed in a refrigerant circulation direction.

5. The refrigeration cycle according to claim 1, wherein said oil comprises polyalkylene glycol.

6. The refrigeration cycle according to claim 1, wherein said oil separating means is disposed at a higher position than said compressor in a vertical direction.

7. The refrigeration cycle according to claim 1, wherein said oil separating means has a centrifugal separation means for separating said refrigerant and said oil by centrifuging said refrigerant and said oil.

8. The refrigeration cycle according to claim 1, wherein said oil separating means has a collision separation means for separating said refrigerant and said oil by a collision of said refrigerant and said oil.

9. The refrigeration cycle according to claim 1, wherein said oil separating means has a trap separation means for separating said refrigerant and said oil by trapping said oil from said refrigerant and said oil.

10. The refrigeration cycle according to claim 1, wherein said oil separating means has a centrifugal separation means for separating said refrigerant and said oil by centrifuging said refrigerant and said oil and a trap separation means for separating said refrigerant and said oil by trapping said oil from said refrigerant and said oil.

11. The refrigeration cycle according to claim 1, wherein said oil separating means has a collision separation means for separating said refrigerant and said oil by a collision of said refrigerant and said oil and a trap separation means for separating said refrigerant and said oil by trapping said oil from said refrigerant and said oil.

12. The refrigeration cycle according to claim 1, wherein a temporary storage section for separated oil is provided at a lower position in a vertical direction in said oil separating means.

13. The refrigeration cycle according to claim 1, wherein an exit for separated oil is provided at a lower end in a vertical direction of said oil separating means.

14. The refrigeration cycle according to claim 1, wherein said refrigeration cycle is used in an air conditioning system for vehicles.