Refrigeration cycle

Abstract: To present a refrigeration cycle of high reliability by controlling, in a refrigeration cycle, deposit of foreign matter at inlet or outlet of a capillary tube in a simple and inexpensive structure, regardless of changeover of cooling operation and heating operation. In a refrigeration cycle using an alternative refrigerant, a junction 3b of a capillary tube 3a composing an expansion device 3 and a piping 5 has a slope 6 gradually decreased in inside diameter from the piping 5 side to the capillary tube 3a side. An end portion of the capillary tube 3a projects into the junction 3b at the piping 5 side. The projecting end of the capillary tube 3a is opened obliquely to the axial line of the capillary tube. A hole is formed in the peripheral wall of the projecting end of the capillary tube 3a. In such constitution, foreign matter in the refrigerant is forced to deposit in other portions than the capillary tube 3a, and the foreign matter is removed from the refrigerant. At the same time, the depositing foreign matter is prevented from having effects on the flow of the refrigerant.

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a refrigeration cycle, and more particularly to a refrigeration cycle connecting a compressor, a condenser, an expansion device, and an evaporator in a loop by piping. In particular, the present invention concerns a refrigeration cycle according to the preamble of present claim 1. Such a refrigeration cycle is already known from the document JP-A-06 159 865 . PRIOR ART The compressor used in refrigeration cycle, in particular, the maintenance-free enclosed compressor is composed of, as disclosed in Japanese Laid-open Patent 62-298680 and others, a compressive mechanism filling an enclosed container with such mixed refrigerant and oil for compressing by sucking refrigerant, an oil pump for feeding the oil into machine sliding parts, and a motor for driving them by drive shaft. On the other hand, the refrigeration cycle was composed by using refrigerant such as chlorofluorocarbons (CFCs) or R12 and designated hydrochlorofluorocarbons (HCFCs) or R22. The specific CFCs are chemically stable, and free from flammability and toxicity as compared with hitherto known refrigerants such as sulfur dioxide and methyl chloride, and are widely applied as ideal refrigerants and have been used for many years. Recently, however, chlorine atoms contained in the molecules of specific CFCs are recognized to induce destruction of the ozone layer, and development and use of alternative refrigerants not containing chlorine atoms have been attempted. As a practical alternative refrigerant, for example, a chlorine-free refrigerant such as hydrofluorocarbon has been proposed (Hydraulic and Pneumatic Technology, June 1994, Nippon Kogyo Shuppan). As an alternative refrigerant, for example, R134a is used. Since chlorine is not contained, however, the alternative refrigerant is not expected to have an excellent lubricity as in the conventional specific CFCs. Accordingly, as the oil to be contained in the enclosed container, an oil compatible with the alter native refrigerant is particularly required. The oil contained in the enclosed container is stirred by the alternative refrigerant discharged from the compressive mechanism into the enclosed container, and is further stirred by rotor of the motor. At this time, if the oil is compatible with the alternative refrigerant, the oil is stirred well with the refrigerant discharged into the enclosed container, and permeates into narrow gaps in the sliding parts of the machines. Therefore, together with the effects of supply of oil by oil pump, the lubricating performance is enhanced. As such oil, as disclosed in Japanese Laid-open Patent 6-235570 , an ester derivative synthetic oil is used. However, when the enclosed compressor is operated in such conditions and the refrigeration cycle is executed and continued, foreign matter may deposits in the inlet and outlet of capillary tubes composing the expansion device, and the flow of the refrigerant is blocked relatively early, and the refrigerating function is lowered. To elucidate the cause of such defect, various experiments were conducted to study. As a result, it was found to be due to the use of the ester oil as the oil compatible with the alternative refrigerant. If moisture invades when enclosing the refrigerant piping, or moisture is formed after enclosing due to some reason, the ester oil is hydrolyzed by the moisture, and produces fatty acid. The fatty acid corrodes the parts in the piping, forms metal soap and produces sludge. The ester oil is low in stability, and therefore foreign matter is likely to be dissolved and mixed in when the temperature is raised, or foreign matter is likely to precipitate when the temperature is lowered. At the inlet of the capillary tube, the flow velocity of the refrigerant drops, and hence the precipitating foreign matter is likely to be adhered to cause clogging. At the outlet of the capillary tube, since the temperature is lowered, foreign matter is likely to precipitate and stick. The above Japanese Laid-open Patent 6-235570 discloses a refrigeration cycle characterized by solving the problems of faulty flow of refrigerant or clogging in the capillary tube, by capturing the foreign matter by installing a filter immediately at the upstream side in the flow direction of the refrigerant in the capillary tube in the midst of the refrigerant piping. However, the above filter structure is complicated and expensive, and it cannot cope with the defect of precipitation due to temperature drop at the outlet of the capillary tube and immediate deposit of the precipitates. In the refrigeration cycle operated by the heat pump, if the flow direction of refrigerant is reverse in changeover of heating and cooling, the filter must be provided at both sides of the capillary tube, which further adds to the cost. It is an object of the invention to present a refrigeration cycle of high reliability capable of suppressing deposit of foreign matter at the outlet or inlet of the capillary tube in a simple and inexpensive structure, regardless of changeover of cooling operation and heating operation. SUMMARY OF THE INVENTION The present invention thus concerns a refrigeration cycle as defined in the appended claims. The refrigeration cycle of the invention comprises a compressor, a condenser, an expansion device, and an evaporator connected in a loop by piping, using an alternative refrigerant, in which the expansion device has a capillary tube and a junction for connecting the capillary tube and piping, the inside diameter of the junction is larger than the inside diameter of the capillary tube and the capillary tube projects freely into the junction. Foreign matter that may impede passing of refrigerant deposits aggressively in the inside space of the connection pipe and an outer surface of the free projecting end of the capillary tube. In particular, the junction has a slope decreasing gradually in the inside diameter from the piping side to the capillary tube side. This slope forms a wide space at the end portion of either inlet or outlet part of the capillary tube, regardless of the direction in which the refrigerant flows. In this constitution, if foreign matter deposits on the inner surface of the connection pipe, the depositing foreign matter does not affect the main flow of the refrigerant in the capillary tube or junction because of the wide space in the junction. Therefore, the refrigerating function of the refrigerating cycle is stable for a long period, and the reliability is enhanced. Moreover, the above effects are obtained only by the improvement of the duct shape of each junction of the capillary tube and piping. Hence, the structure is simple and inexpensive. In whichever direction the refrigerant may flow, the end portion at the inlet or outlet of the capillary tube projects freely into the junction of larger diameter than the end portion, and the flow of refrigerant is stagnant between the outer surface of the protrusion and the wide inner surface of the junction of the piping side, so that much foreign matter deposits aggressively on the outer surface of the protrusion and inside of the junction and in the space between them. Moreover, the depositing foreign matter has no effect on the main flow of the refrigerant in the capillary tube and junction. Still more, clogging of capillary tube can be prevented for a longer period. Therefore, the refrigerating function of the refrigerating cycle is stable for a long period, and the reliability is enhanced. Moreover, the above effects are obtained by the improvement of the connection state of each junction of the capillary tube and piping. Hence, the structure is simple and inexpensive. Further, the junction possesses an oleophilic treated inner surface. In the above constitution, the junction has a slope gradually decreasing in inside diameter from the piping side to the capillary tube side. The structure is not complicated, and the actions and effects as above are obtained. In the constitution, the projecting end of the capillary tube is particularly preferred to be opened obliquely to the axial line of the capillary tube. By thus constituting, the opening area of the piping side of the capillary tube to the wide space side is large, and therefore the foreign matter is less likely to be caught in the opening of the projecting end at the inlet and outlet of the capillary tube, so that foreign matter deposit preventive function at the capillary tube inlet and outlet may be further enhanced. In the constitution, it is particularly preferred that a hole is provided in the peripheral wall of the projecting end of the capillary tube. By thus constituting, entering or leaving of the refrigerant between the projecting end of the capillary tube and wide junction at the piping side may be smoothed by the hole, and this smooth flow of refrigerant interferes deposit of foreign matter on the end portion at the inlet or outlet of the capillary tube. Therefore, by a simple additional condition of forming a hole, the foreign matter deposit preventive function at the inlet and outlet of the capillary tube may be further enhanced. In the constitution, the capillary tube for composing the expansion device comprises plural capillary tubes differing at least in the inside diameter or length, and it is particularly preferred that these plural capillary tubes are connected parallel. By thus constituting, foreign matter clogging occurs in the sequence of difficulty of flow of refrigerant (that is, from the capillary tube having smaller inside diameter or longer capillary tube). Therefore, early clogging of the entire capillary tubes is prevented, and a normal function is maintained for a long period. That is, only the number of capillary tubes is increases, and in proportion to the increase in the number of capillary tubes, the required diameter of capillary tubes is smaller or shorter in length, so that the structure is not particularly complicated. In the constitution, it is particularly preferred that a slope connected in batch with each capillary tube, gradually increasing in the inside diameter from the piping side to each capillary tube side, is formed in the junction of the plural capillary tubes and piping. By thus constituting, utilizing the space wider than the piping by the slope, plural capillary tubes can be connected in batch. By a simple structure of increasing only the junction, effects of deposit of foreign matter on the flow of refrigerant and occurrence of clogging may be notably prevented by the wide space. In the constitution, preferably, each capillary tube should be projected into the slope. By thus constituting, the intrinsic actions and effects as mentioned above can be exhibited. In the constitution, the projecting ends of the capillary tubes are particularly preferred to be opened obliquely to their axial line. By thus constituting, the intrinsic actions and effects as mentioned above can be exhibited. In the constitution, preferably, a hole should be provided in the peripheral wall of the projecting end of capillary tube. By thus constituting, the intrinsic actions and effects as mentioned above can be exhibited. In the constitution, preferably, the capillary tube for composing the expansion device comprises plural capillary tubes, and each one of the plural capillary tubes has an valve. The capillary tubes in use can be assembled into one by opening or closing the valves, and the capillary tubes in use can be sequentially changed over depending on the degree of clogging of the capillary tubes with foreign matter. By thus constituting, early clogging of the entire capillary tubes is prevented. The changeover control is effected by the method of utilizing the control means for operation control of the refrigeration cycle itself, and a normal function can be maintained for a long period without particularly complicating the structure. A different refrigeration cycle of the invention comprises a compressor, a condenser, an expansion device, and an evaporator connected in a loop by piping, using an alternative refrigerant, and further comprises a heat pump changeover valve. The expansion device comprises plural capillary tubes, and a junction for connecting the capillary tubes and a piping, and the plural capillary tubes have individually a one-way valve, and are connected so that the direction of the one-way valves may be opposite to each other. By thus constituting, by changeover of cooling operation and heating operation, if the flow direction of refrigerant is inverted, by limitation of flow direction by one-way valve, the passing capillary tubes of the refrigerant in cooling operation and heating operation can be used selectively. Therefore, clogging of capillary tubes due to foreign matter can be reduced to half. In the above constitution, the expansion device possesses plural capillary tubes, and the plural tubes are connected in series through the connection pipes provided among them. The connection pipes have a larger inside diameter than the inside diameter of the capillary tubes. Since the inside diameter of the connection pipes is wider, the refrigerant is caused to flow stagnantly, and foreign matter can be deposited by force to be removed from the refrigerant, so that adhesion to the capillary tubes can be prevented. The capillary tubes can be divided by the connection pipes so that the foreign matter may not affect the flow of the refrigerant, and the actual length of capillary tubes is shortened to several times smaller than the required length, so that foreign matter may hardly deposit on the capillary tubes. In the constitution, preferably, the inner surface of the capillary tubes should have a smooth layer. By the smoothness of the smooth layer in the inner surface of the capillary tube, foreign matter is less likely to be caught or adhered. In the constitution, preferably, the inner surface of the capillary tubes for composing the expansion device should have a parting process surface treated for parting. Therefore, foreign matter is less likely to deposit on the parting surface of the inner surface of the capillary tube. In the constitution, preferably, the inner surface of the capillary tubes for composing the expansion device should have a hydrophilic layer treated for hydrophilic property. Therefore, deposit of oily foreign matter can be prevented by hydrophilic property of the inner surface of the capillary tubes. In the constitution, the inside diameter of the junction of the capillary tubes for composing the expansion device and the piping should be larger than the inside diameter of the capillary tubes, and moreover the inner surface of the junction should have an oleophilic surface processed by oleophilic treatment. By sticking oily foreign matter aggressively to the inner surface of a wide oleophilic surface of the junction, the foreign matter in the refrigerant can be removed, and at the same time, effects of the foreign deposit on the flow of refrigerant can be eliminated. Hence, foreign matter is less likely to deposit on the inner surface of the inlet and outlet of the capillary tubes. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of refrigeration cycle of heat pump type. Fig. 2 is a sectional view showing a connection structure, which does not form part of the present invention, of piping and expansion device in Fig. 1. Fig. 3 is a sectional view showing a connection structure of piping and expansion device in a first embodiment of the invention. Fig. 4 is a sectional view showing a connection structure of piping and expansion device in a second embodiment of the invention. Fig. 5 is a sectional view showing a connection structure of piping and expansion device in a third embodiment of the invention. Fig. 6 is a sectional view showing a connection structure of piping and expansion device not forming part of the invention. Fig. 7 is a sectional view showing a connection structure of piping and expansion device not forming part of the invention. Fig. 8 is a sectional view showing a connection structure of piping and expansion device in a fourth embodiment of the invention, and a block diagram of control means. Fig. 9 is a sectional view showing a connection structure of piping and expansion device in an fifth embodiment of the invention. Fig. 10 is a sectional view showing a connection structure of piping and expansion device in an sixth embodiment of the invention. Fig. 11 is a sectional view showing part of capillary tubes for composing an expansion device in a seventh embodiment of the invention. Fig. 12 is a sectional view showing part of capillary tubes for composing an expansion device in a eighth embodiment of the invention. Fig. 13 is a sectional view showing part of capillary tubes for composing an expansion device in an ninth embodiment of the invention. Fig. 14 is a sectional view showing a connection structure of piping and expansion device of the invention. Fig. 15 is a sectional view showing a connection structure of piping and expansion device in the first embodiment of the invention. Reference Numerals 1 Compressor 2 Condenser 3 Expansion device 3a, 3e to 3k, 3m, 3n, 3p to 3s Capillary tubes 3b Junction 3c Projecting end 3d Hole 4 Evaporator 5 Piping 6, 7 Slopes 6a, 7a Spaces 8, 9, 10 Valves 11, 12 One-way valves 13 Connection pipe 20 Four-way valve 21 Smoothed surface 22 Parting treated layer 23 Hydrophilic treated layer 24 Rough surface 25 Oleophilic treated layer DESCRIPTION OF THE PREFERRED EMBODIMENTS A schematic diagram of refrigeration cycle of heat pump type is illustrated in Fig. 1. In Fig. 1, the refrigeration cycle is composed by connecting a compressor 1, a condenser 2, an expansion device 3, and an evaporator 4 in a loop by means of a piping 5, using an alternative refrigerant. Using a synthetic oil compatible with the alternative refrigerant, whether this refrigeration cycle is operated by changing over between cooling operation and heating operation, foreign matter mixed in the refrigerant may adhere to the inlet or outlet of the capillary tubes. In the midst of the piping 5, there is a four-way valve (not shown) for changing over between cooling operation and heating operation. In cooling operation, the refrigerant flows in the direction indicated by arrow into the condenser 2, expansion device 3 and evaporator 4 as shown in Fig. 1. In heat pump operation, the refrigerant flows reversely. Hence, the condenser 2 in cooling operation functions as evaporator, and the evaporator 4 functions as condenser. In such refrigeration cycle, as the synthetic oil compatible with the alternative refrigerant, for example, an ester oil is used, and in cooling operation or heating operation, the foreign matter mixing in or precipitating in the refrigerant is likely to deposit on the end portions at the inlet and outlet of the capillary tubes 3a for composing the expansion device 3, in particular, on the inner surface. By such deposit of foreign matter, flow of refrigerant is blocked early, or clogging occurs, and thereby the function of the refrigeration cycle is often lowered early. A connection structure, which does not form part of the present invention, of the piping 5 and expansion device 3 is shown in Fig. 2. As shown in Fig. 2, at the junction 3b of the capillary tube 3a and piping 5 forming the expansion device 3, a slope 6 decreasing gradually in inside diameter from the piping 5 side to the capillary tube 3a side is provided. This slope 6 forms a wide space 6a at both ends at the inlet and outlet of the capillary tube 3a regardless of the direction of flow of the refrigerant. If foreign matter deposits on the inner surface of the space 6a, the depositing foreign matter does not affect the main flow of the refrigerant in the capillary tube 3a and junction 3b because the space of the junction 3b is wide. Moreover, closing of the capillary tube 3a is prevented, and the refrigeration function of the refrigeration cycle is stable for a long period, and a high reliability is obtained. Still more, only by the improvement of duct shape of each junction 3b of the capillary tube 3a and piping 5, the above effects are obtained, and hence the refrigeration cycle of simple structure and low cost is obtained. In the embodiment, the junction 3b is formed separately, not integrated with the piping 5 and capillary tube 3a. Therefore, the piping 5, capillary tube 3a and junction 3b are mutually linked together, and the slope shape of the junction 3b can be easily formed by processing of an independent part. Also in the embodiment, this independent junction 3b is fitted externally to the end of the piping 5 and capillary tube 3a, and therefore this connection structure itself can expand the space of the junction 3b having the slope 6, and the effect of the deposit of foreign matter on the flow of refrigerant can be reduced, which is advantageous for long-term stability of the function of the refrigeration cycle. The junction 3b can be also formed integrally with one or both of the piping 5 and capillary tube 3a. The junction 3b is, together with the piping 5 and capillary tube 3a, made of copper as usual, and they can be joined by brazing. Other material and joining structure may be also possible. (Embodiment 1) A connection structure of piping and expansion device in a first embodiment is shown in Fig. 3. This embodiment is based on the structure of the above embodiment, and same members are identified with same reference numerals, and duplicate explanations are omitted. In Fig. 3, the capillary tube 3a forming the expansion device 3 projects to the inside of the junction 3b at the piping 5 side. In whichever direction the refrigerant flows, the end portion at the inlet or outlet of the capillary tube 3a projects to the inside of the junction 3b having a wide space 6a larger in diameter than the end portion, and the flow of the refrigerant is stagnant in the portion 6b between the outer side of the projecting end portion 3c and the inner side of the wide junction 3b at the piping 5 side. Therefore, in the portion 6b between the outer side of the projecting end portion 3c and the inner side of the junction 3b, much foreign matter deposits, and this depositing foreign matter does not affect the main flow of the refrigerant in the capillary tube 3a and junction 3b. In this constitution, closing of the capillary tube 3a is prevented for a longer period, and hence the refrigeration function of the refrigeration cycle is stable for a longer period than in the first embodiment, and the reliability is notably enhanced. Moreover, only by the improvement of the connection state of each junction 3b of the capillary tube 3a and piping 5, the above effects are obtained, and the refrigeration cycle of simple structure and low cost is obtained. Incidentally, the connection structure of the embodiment is not limited to the constitution shown in Fig. 1, but, for example, the end portion of the capillary tube 3a of small diameter may project from the end plate closing the end portion of the piping 5 of larger diameter to the inner side of the piping 5. In this constitution, the intrinsic actions and effects of the embodiment are exhibited, and the function of the refrigeration cycle can be stabilized for a long period to a certain extent. Further, as shown in Fig. 15, the inside of the junction 3b of the expansion device 3 has an oleophilic treated layer 25. Oily foreign matter is forced to deposit on oleophilic inner surface and the inside of the slope 6 having a wide space 6b, so that foreign matter may hardly deposit on the inside of the capillary tube 3a and other parts. Therefore, the reliability of the refrigeration cycle is enhanced. Moreover, it is inexpensive without particularly complicating the structure. Oleophilic treatment is done by film coating with alcoholic resin or the like. As described herein, in whichever direction the refrigerant may flow in cooling operation or heating operation, deposit of foreign matter at the end portion at the inlet or outlet of the capillary tube is prevented, and blocking of flow of refrigerant and closing of capillary tube can be prevented. As a result, the refrigeration function of the refrigeration cycle can be stabilized for a long period, and the reliability is enhanced. Moreover, since the structure is not particularly complicated, it is also inexpensive. (Embodiment 2) A second embodiment is based on the first embodiment, and same members are identified with same reference numerals, and the characteristic points of the embodiment are described below. A connection structure of piping and expansion device in the embodiment is shown in Fig. 4. In Fig. 4, a projecting end 3c of the capillary tube 3a is opened obliquely to the axial line of the capillary tube 3a, and the obliquely opened projecting end 3c projects to the inside of the junction 3b. In this constitution, the opening area of the capillary tube 3a to the wide space 6a side of the piping 5 side is wider, so that foreign matter is hardly caught in the opening of the projecting end 3c at the inlet or outlet of the capillary tube 3a. As a result, without complicating the structure, the preventive effect of deposit of foreign matter at the inlet or outlet of the capillary tube 3a is further enhanced. Meanwhile, the embodiment is not always limited to the constitution of the first embodiment. (Embodiment 3) A third embodiment is based on the first embodiment, and same members are identified with same reference numerals, and the characteristic points of the embodiment are described below. A connection structure of piping and expansion device in the embodiment is shown in Fig. 5. In Fig. 5, a hole 3b is formed in the peripheral wall of the projecting end 3c of the capillary tube 3a. In this constitution, entering or leaving of refrigerant between the capillary tube 3a and wide junction 3b at the piping 5 side is smoothed by the hole 3b, and this smooth flow of refrigerant interferes deposit of foreign matter on the projecting end 3c at the inlet or outlet of the capillary tube 3a, so that the preventive effect of deposit of foreign matter at the inlet or outlet of the capillary tube 3a is further enhanced. Example not forming part of the invention A connection structure of piping and expansion device is shown in Fig. 6. In Fig. 6, as the capillary tube for composing the expansion device 3, plural capillary tubes differing in inside diameter are installed. For example, three capillary tubes 3e, 3f, 3g project to the inside of the junction 3 and are connected. In this constitution, the capillary tubes are clogged sequentially from the one 3g smallest in inside diameter where the refrigerant flows most hardly, and early clogging of the entire capillary tubes 3e to 3g is prevented, so that the normal function can be maintained for a longer period. Only the number of capillary tubes 3e, 3f, 3g is increased, and in proportion to increase in the number of capillary tubes 3e, 3f, 3g, the required tube diameter of the capillary tubes 3e, 3f, 3g can be reduced, and hence the structure is not particularly complicated. The junction 3b of the plural capillary tubes 3e, 3f, 3g and the piping 5 has a slope 7 gradually increasing in the inside diameter from the piping 5 side to the side of the capillary tubes 3e, 3f, 3g. The junction 3b has a wider space 7a than the piping 5 owing to this slope 7. By making use of this wide space 7a, the plural capillary tubes 3e to 3g can be connected in batch. Moreover, by this wide space 7a, effects of deposit of foreign matter on the refrigerant and occurrence of clogging can be further prevented. 3g into the slope 7, the outer surface of each projecting end 3c of the slope 7, and the portion 7b between them can exhibit the same actions and effects as in the first embodiment. Example not forming part of the invention A connection structure of piping and expansion device is shown in Fig. 7. In Fig. 7, instead of the plural capillary tubes differing in diameter in the previous example, plural capillary tubes 3h, 3i, 3j differing in length are connected in parallel. In this constitution, the capillary tubes are clogged sequentially from the one 3h largest in length where the refrigerant flows most hardly, and early clogging of the entire capillary tubes 3h, 3i, 3j is prevented, so that the normal function can be maintained for a longer period. Only the number of capillary tubes 3h to 3j is increased, and in proportion to increase in the number of capillary tubes 3h, 3i, 3j, the required tube diameter of the capillary tubes 3h to 3j can be reduced, and hence the structure is not particularly complicated. (Embodiment 4) A connection structure of piping and expansion device in a fourth embodiment is shown in Fig. 8. As shown in Fig. 8 (a), plural capillary tubes 3k, 3m, 3n composing the expansion device 3 respectively possess valves 8 to 10, and are connected to the piping 5. By opening or closing of the valves 8 to 10, opening or closing of the three capillary tubes 3k, 3m, 3n to be used is changed over sequentially. This constitution prevents early clogging of the entire capillary tubes 3k, 3m, 3n. Changeover of the valve 8 is controlled by control means for operation control of the refrigeration cycle itself, for example, by microcomputer MC as shown in Fig. 8 (b), so that a normal function can be maintained for a long period without particularly complicating the structure. For such control, every time a clogging signal is received either automatically or manually, the microcomputer MC sequentially changes over the valves 8 to 10, thereby changing over the capillary tubes 3k, 3m, 3n to be used. For such automatic changeover, meanwhile, the microcomputer MC can obtain a clogging signal automatically by judging the passing resistance of refrigerant in the capillary tubes 3k, 3m, 3n being used by an internal function for detecting an abnormal pressure rise of refrigerant or the like. (Embodiment 5) A connection structure of piping and expansion device in an fifth embodiment is shown in Fig. 9. This embodiment is to replace the fourth embodiment, and belongs to the refrigeration cycle having a heat pump changeover valve same as shown in Fig. 1. As shown in Fig. 9, the expansion device 3 possesses capillary tubes 3p, 3q provided with one-way valves 11, 12 respectively, and these two capillary tubes 3p, 3q are connected parallel so that the direction of the mutual one-way valves 11, 12 may be opposite to each other. In cooling operation and heating operation, the flow direction of refrigerant is mutually opposite, and corresponding to this, by the flow direction control by the one-way valves 11, 12, the passing capillary tube of refrigerant is changed over in cooling operation and heating operation. Therefore, clogging of the capillary tubes 3p, 3q due to deposit of foreign matter can be reduced to half. As a result, the reliability of the refrigeration cycle is enhanced, and the cost is lowered without complicating the structure. In the constitution, it is also possible to design the capillary tube having the one-way valve 11 and the capillary tube having the one-way valve 12 at different diameter or length, so that the plural capillary tubes may be clogged sequentially. (Embodiment 6) A connection structure of piping and expansion device in an sixth embodiment is shown in Fig. 10. This embodiment is based on the refrigeration cycle shown in Fig. 1. As shown in Fig. 10, plural capillary tubes for composing the expansion device 3, for example, two capillary tubes 3r, 3s are connected in series through a connection pipe 13 provided between them, and the inside diameter of the connection pipe 13 is larger than the inside diameter of the capillary tubes 3r, 3s. In this constitution, the refrigerant is caused to stay stagnant in the connection pipe 13 having the larger inside diameter so that foreign matter may deposit by force. Thus, foreign matter is removed from the refrigerant, and deposit of foreign matter on the capillary tubes can be prevented. Moreover, by the connection pipe 13 for preventing effects of foreign matter on the flow of refrigerant, the capillary tubes can be divided, and the actual length of the capillary tubes may be shortened several times smaller than the required length, and deposit of foreign matter on the capillary tubes can be further prevented. As a result, the reliability of the refrigeration cycle is enhanced. At the same time, it is inexpensive without particularly complicating the structure. The embodiment may be also combined with the first to fifth embodiments, and the individual intrinsic actions and effects can be exhibited in such constitution. (Embodiment 7) Fig. 11 is a sectional view of part of a capillary tube for composing the expansion device in a seventh embodiment. This embodiment is based on the refrigeration cycle of Fig. 1. As shown in Fig. 11, the inside of the capillary tube 3a for composing the expansion device 3 has a smoothed surface 21. By the smoothness of the smoothed surface 21 of the inside of the capillary tube 3a, foreign matter is hardly caught or adhered. Therefore, the reliability of the refrigeration cycle is enhanced. Moreover, it is inexpensive without particularly complicating the structure. Smoothing process may be done by blast processing, other polishing process, plating, or any other known method. (Embodiment 8) Fig. 12 is a sectional view of part of a capillary tube for composing the expansion device in an eighth embodiment. This embodiment is based on the refrigeration cycle of Fig.1. As shown in Fig. 12, the inside of the capillary tube 3a for composing the expansion device 3 has a releasing treated layer 22. By the lubricating or releasing property of the releasing treated layer 2 foreign matter is hardly or adhered to the inside of the capillary tube 3a. Therefore, the reliability of the refrigeration cycle is enhanced. Moreover, it is inexpensive without particularly complicating the structure. Parting process may be done by for example, fluorine coating process, or any other known method. (Embodiment 9) Fig. 13 is a sectional view of part of a capillary tube for composing the expansion device in a ninth embodiment. This embodiment is based on the refrigeration cycle of Fig.1. As shown in Fig. 13, the inside of the capillary tube 3a for composing the expansion device 3 has a hydrophilic treated layer 23. By the hydrophilic property of the hydrophilic treated layer 23, oily foreign matter is hardly adhered to the inside of the capillary tube 3a. Therefore, the reliability of the refrigeration cycle is enhanced. Moreover, it is inexpensive without particularly complicating the structure. The hydrophilic treated layer 23 is preferably a composition containing, for example, many nitrogen or sulfur atoms, and a nitride treated layer is particularly preferred. It may be also formed by any other known method. Example not forming part of the invention A connection structure of piping and expansion device is shown in Fig. 14. This example is based on the constitution of Fig. 1. As shown in Fig. 14, the inside diameter of the junction 3b of the capillary tube 3a for composing the expansion device 3 and piping 5 is set larger than the inside diameter of the capillary tube 3a, and a wide space 6a is provided. Moreover, the inside of the junction 3b has a roughened surface 24. Foreign matter is forced to deposit on the roughened surface 24 and the inside of the slope 6 having the wide space 6a, and foreign matter in the refrigerant can be removed. At the same time, the depositing foreign matter is prevented from having effects on the flow of the refrigerant. Therefore, foreign matter hardly deposits on the inner surface of the inlet and outlet of the capillary tube 3a. As a result, the reliability of the refrigeration cycle is enhanced. Moreover, it is inexpensive without particularly complicating the structure. Roughening process can be done by chemical etching or blast process. Not limited to them, however, any other known method may be employed.

Claims: A refrigeration cycle comprising: a compressor (1), a condenser (2), an expansion device (3), and an evaporator (4), piping (5) connecting said compressor, said condenser, said expansion device, and said evaporator in a loop, and refrigerant circulating in said compressor, said condenser, said expansion device, said evaporator, and said piping, said refrigerant being a compound not containing chlorine atom in its chemical formula, said expansion device (3) including a capillary tube (3a), and connecting means for connecting said capillary tube and said piping (5), said connecting means being a connection pipe (3b) having a larger inside diameter than the inside diameter of said capillary tube (3a), characterised in that an end portion (3c) of said capillary tube (3a) projects freely into the inside of said connection pipe (3b) so that any foreign matter interfering with the flow of said refrigerant deposits in an inside space (6b) of said connection pipe (3b) and an outer surface of said free projecting end (3c), in that said connection pipe (3b) possesses a slope (6) gradually decreasing in inside diameter from said piping side to said capillary tube side, and in that said connection pipe (3b) possesses an oleophilic treated inner surface. A refrigeration cycle of claim 1, wherein said end portion (3c) of said capillary tube (3a) has an oblique opening with respect to the axial line of said capillary tube (3a). A refrigeration cycle of claim 1, wherein a hole (3d) is formed in a peripheral wall of said projecting end portion (3c) of said capillary tube (3a). A refrigeration cycle of claim 1, wherein said capillary tube comprises plural capillary tubes, and said connection pipe (3b) comprises plural connection pipes for connecting said plural capillary tubes and said piping. A refrigeration cycle of claim 4, wherein said plural capillary tubes mutually differ at least in one of inside diameter and length. A refrigeration cycle of claim 5, wherein each one of said plural connecting means is a connection pipe (3b) having a slope (7) gradually decreasing in inside diameter from said piping side to said capillary tube side. A refrigeration cycle of claim 5, wherein an end portion (3c) of each one of said capillary tubes is projecting to the inside of said connecting means. A refrigeration cycle of claim 7, wherein said projecting end portion (3c) of each one of said capillary tubes has an oblique opening with respect to the axial line of said capillary tube. A refrigeration cycle of claim 7, wherein a hole is formed in the peripheral wall of said projecting end portion of each one of said capillary tubes. A refrigeration cycle of claim 4, wherein each one of said plural capillary tubes (3k, 3m, 3n) possesses a valve (8, 9, 10) for controlling passing of said refrigerant, said valve (8) of only one of said plural capillary tubes is opened by controlling said valve to allow said refrigerant to pass through the opened capillary tube, and only the valve of other capillary tube is opened by sequential control of said valves of said plural capillary tubes to allow said refrigerant to pass through the opened capillary tube. A refrigeration cycle of claim 4, wherein each one of said plural capillary tubes (3p, 3q) possesses a one-way valve (11, 12), one of said plural capillary tubes allows said refrigerant to pass in one specific direction by the action of said one-way valve, and other one of said plural capillary tubes allows said refrigerant to pass in a reverse direction of said specific direction by the action of said one-way valve. A refrigeration cycle of claim 4, wherein said individual capillary tubes (3r, 3s) are mutually connected in series through said individual connecting means, and said individual connecting means are connection pipes having a larger inside diameter than said individual capillary tubes. A refrigeration cycle of claim 1, wherein said capillary tube (3a) has a smoothed inner surface (21). A refrigeration cycle of claim 1, wherein said capillary tube (3a) has a hydrophilic treated inner surface (23).

Inventors: FUJITAKA AKIRA, HANEDA KANJI, KOBAYASHI YOSHINORI, NUMOTO HIRONAO, WAKABAYASHI HISAO, WATANABE SHINJI, WATANABE YUKIO, YAKUMARU YUICHI, YAMAGUCHI NARITO, FUJITAKA, AKIRA, HANEDA, KANJI, KOBAYASHI, YOSHINORI, NUMOTO, HIRONAO, WAKABAYASHI, HISAO, WATANABE, SHINJI, WATANABE, YUKIO, YAKUMARU, YUICHI, YAMAGUCHI, NARITO, Watanabe, Yukio, 1108 Coop Nomura Kyotominami
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD
Application year: 1996
Main classification: F25B41
IPC codes: F25B13, F25B41