Patent Publication Number: US-2012037554-A1

Title: Oil Separator

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to an oil separator which separates refrigeration machine oil mixed in refrigerant discharged from a compressor, and specifically, to an oil separator suitable to be disposed in a refrigeration circuit of an air conditioning system for a vehicle. 
     BACKGROUND ART OF THE INVENTION 
     For example, in a refrigeration circuit of an air conditioning system for a vehicle, there may be a case where provided is an oil separator having a function for separating refrigeration machine oil mixed in refrigerant discharged from a compressor and returning the separated refrigeration machine oil to the compressor. In a conventional oil separator, because the outer shape and the length dimension are large, the mounting position to an automobile has been limited, and further, because the structure is relatively complicated and the cost is high, it has not been so common to separate oil in refrigerant discharged from a compressor by an oil separator disposed outside the compressor and to return the separated refrigeration machine oil to the compressor. Therefore, an oil separating mechanism incorporated integrally into a compressor itself has been common, but in such a case, the function for oil separation has been limited. 
     Further, for example, in refrigerant HFO1234yf, etc. planned to be used from the viewpoint of preventing global warmth, because its temperature for separation into two layers of refrigerant and refrigeration machine oil in a high temperature region is relatively low as compared with a conventional refrigerant HFC134a, oil return to a compressor in a refrigeration circuit may deteriorate, and further, because performance of refrigeration system may be considered to deteriorate from its refrigerant property, it is considered to be necessary to decrease the amount of oil to be circulated in the refrigeration circuit itself, improve the efficiency of the air conditioning system and realize a performance level nearly equal to that of HFC134a. 
     For example, as a prior art, as disclosed in Patent document 1, a compressor built-in type oil separator aiming its compact structure has been considered. Where, in the example disclosed in this Patent document 1, in a conventional type oil separator which has an outer tube for generating a whirl flow of refrigerant containing refrigeration machine oil introduced thereinto and an inner tube for leading refrigerant, separated from oil at a whirl flow inversion part, to outside, a structure is employed wherein the outer tube is divided into a whirl flow separation part relatively small in cross section of flow path and a whirl flow inversion chamber relatively large in cross section of flow path, as the refrigerant and the oil are flowing from the whirl flow separation part varying the cross-sectional area of flow path to the whirl flow inversion chamber, its flow speed is reduced, and it is aimed that the oil dropped down to the bottom of the outer tube can be stably accumulated. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent document 1: JP-A-2005-180808 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the above-described oil separator structure disclosed in Patent document 1, outflow of the oil stored in the lower part into the outlet pipe (inner tube) due to splashing up cannot be avoided, and consequently, it is difficult to realize an excellent oil separation performance. Further, because a structure is employed wherein the diameter of the outer tube is enlarged partially, large-sized form in the radial direction as the whole of the oil separator cannot be avoided, and therefore, it is a disadvantageous structure less in freedom on space for disposition in refrigeration circuit or space for being mounted. Furthermore, although in the above-described Patent document 1 there is a description of a structural example which employs an improvement for enlarging the pipe diameter of the entrance of the outlet pipe provided as a return pipe in order to reduce the pressure loss in return flow to the outlet pipe of the separator, this causes the oil to be liable to enter into the outlet pipe further easily, and the amount of oil flowing out from the outlet pipe toward outside (for example, toward a condenser in the refrigeration circuit) may increase. 
     Accordingly, an object of the present invention is to provide an oil separator which can separate refrigerant and refrigeration machine oil with extremely high efficiency, which can effectively prevent the outflow of separated oil towards the refrigerant discharge path side, and which can reduce pressure loss in the flow of refrigerant. 
     Further, another object of the present invention is to provide an oil separator which can realize a compact structure without making it large-sized especially in the radial direction while achieving an excellent separation performance, which can spatially improve mounting property in case of being mounted as a sole body, and which can be easily designed to be integrated with another device. 
     Means for Solving the Problems 
     To achieve the above objects, an oil separator according to the present invention comprises: 
     a tubular outer pipe which is disposed on a compressor outlet side so as to extend in a vertical direction; 
     an inlet pipe provided at an upper part of the tubular outer pipe for introducing refrigerant containing refrigeration machine oil, discharged from a compressor, into the tubular outer pipe in such a manner as to produce a downward helical flow of refrigerant containing refrigeration machine oil along an inner surface of the tubular outer pipe; 
     a refrigerant outlet pipe which has an external outflow port at an upper end for flowing out refrigerant to outside the tubular outer pipe, has a section extending in an axial direction of the tubular outer pipe at a central position of the tubular outer pipe, and has a first refrigerant inflow port at a lower end of the section for flowing in refrigerant therein, which has been separated from refrigerant containing refrigeration machine oil having flowed down in the helical flow and the flow direction of which has been inverted in relation to vertical direction at a first refrigerant inversion part; 
     a refrigerant return pipe which extends in an axial direction of the tubular outer pipe at a central position of the tubular outer pipe, below the refrigerant outlet pipe, has a refrigerant communication port at an upper end for being confronted with or connected to a lower end of the refrigerant outlet pipe, and has a second refrigerant inflow port at a lower end for flowing in refrigerant therein, which has been separated from refrigerant containing refrigeration machine oil having flowed down in the helical flow and the flow direction of which has been inverted in relation to vertical direction at a second refrigerant inversion part; and 
     an oil storage part, which is formed at a bottom of the tubular outer pipe, capable of temporarily storing refrigeration machine oil separated from refrigerant, 
     wherein a part exhibiting a reflector function for preventing refrigeration machine oil stored in the oil storage part from flowing out into the refrigerant outlet pipe is provided between the refrigerant return pipe and the inner surface of the tubular outer pipe. 
     In such an oil separator according to the present invention, although the refrigeration machine oil having a greater mass is separated from the refrigerant by centrifugal separation in the helical flow of the refrigerant containing refrigeration machine oil in the tubular outer pipe, in the downflow direction of this helical flow two refrigerant inversion parts of the first refrigerant inversion part and the second refrigerant inversion part are provided, and by inverting the flow direction of refrigerant in relation to vertical direction at each refrigerant inversion part, the refrigerant is separated from the refrigerant containing refrigeration machine oil (as viewed from the oil side, the refrigeration machine oil is separated from the refrigerant containing refrigeration machine oil). The refrigerant separated at the first refrigerant inversion part enters into the refrigerant outlet pipe from the first refrigerant inflow port, and is flowed out from the external outflow port to outside of the oil separator through the refrigerant outlet pipe, and the refrigerant separated at the second refrigerant inversion part enters into the refrigerant return pipe from the second refrigerant inflow port, and is flowed out from the external outflow port to outside of the oil separator through the refrigerant return pipe, the refrigerant communication port and successively the refrigerant outlet pipe. Therefore, the separation of refrigeration machine oil and refrigerant is carried out at two steps in the axial direction of the tubular outer pipe, and as compared with a conventional single-step separation, the efficiency of separation can be improved. Then, the part exhibiting a reflector function is provided between the refrigerant return pipe and the inner surface of the tubular outer pipe, namely, between the first refrigerant inversion part and the second refrigerant inversion part, and it can be prevented by the reflector effect due to the part exhibiting a reflector function that the refrigeration machine oil stored in the oil storage part at the bottom of the tubular outer pipe flows out into the refrigerant outlet pipe through the first refrigerant inflow port by splashing up, etc. Since return of oil into the separated refrigerant due to splashing up, etc. can be prevented, also from this point of view, the efficiency of separation can be improved. Further, because this part exhibiting a reflector function also exhibits a function for temporarily contracting the cross-sectional area of flow path with respect to the downflow of the helical flow of the refrigerant containing refrigeration machine oil, can also be expected improvement of the inversion and separation performance of refrigerant at the first refrigerant inversion part positioned at an upstream side of the part exhibiting a reflector function, improvement of separation performance due to the helical flow at a downstream side of the part exhibiting a reflector function by temporarily increasing the flow speed by temporarily contracting the cross-sectional area of flow path, and further, improvement of the inversion and separation performance of refrigerant at the second refrigerant inversion part due to enlargement of the cross-sectional area of flow path after the temporary contraction of the cross-sectional area of flow path. As a result, the efficiency for separation as the whole of the oil separator can be greatly improved. Further, because the separation due to the above-described two-step refrigerant inversion and the inflow operation of the separated refrigerant from both refrigerant inversion parts into the discharge path are performed, as compared with a conventional single-step case, reduction of resistance at the refrigerant inversion parts can be expected, and whereby reduction of resistance of flow path and pressure loss as the whole of the oil separator becomes possible. Furthermore, because, by the discharge operation of the refrigerant separated at the first refrigerant inversion part through the refrigerant outlet pipe, inducing effect from the second refrigerant inflow port of the refrigerant return pipe, of the refrigerant separated at the second refrigerant inversion part, can also be expected, an efficient discharge of separated refrigerant becomes possible, and as the whole of the oil separator, further reduction of resistance in refrigerant flow path and pressure loss becomes possible. 
     Further, in the oil separator according to the present invention, the diameter of the tubular outer pipe may be a constant diameter, and because in this tubular outer pipe two refrigerant inversion parts of the first refrigerant inversion part and the second refrigerant inversion part and the part exhibiting a reflector function therebetween can be formed, there is no portion enlarged in outer diameter of oil separator and it is not necessary to make it partially large-sized in the radial direction as in the aforementioned Patent document 1, and therefore, a compact structure can be realized particularly in the radial direction. Therefore, spatially, the mounting property in case of being mounted as a sole body, in particular, the space efficiency, can be improved. Further, a tubular outer pipe having a constant diameter may be employed, it also becomes possible to facilitate integration with another device, for example, a condenser disposed at a downstream position of a compressor in a refrigeration circuit. 
     In the oil separator according to the present invention exhibiting such an excellent performance, as more concrete structures of the above-described refrigerant return pipe and the above-described part exhibiting a reflector function, various structures can be employed. For example, a structure can be employed wherein the refrigerant return pipe comprises a tubular pipe having a constant diameter which extends upwardly from the second refrigerant inversion part, and the part exhibiting a reflector function comprises a bevel part which extends from an upper end of this tubular pipe toward an obliquely downward direction and which is enlarged in diameter as located at a lower position. 
     Alternatively, a structure may be employed wherein the refrigerant return pipe comprises a bell mouth type pipe which extends upwardly from the second refrigerant inversion part and which is enlarged in diameter as located at an upper position, and the part exhibiting a reflector function is formed from the bell mouth type pipe. 
     Alternatively, a structure may be employed wherein the refrigerant return pipe comprises a tubular pipe part having a constant diameter which extends upwardly from the second refrigerant inversion part and a bell mouth type pipe part which extends upwardly from an upper end of the tubular pipe part and which is enlarged in diameter as located at an upper position, and the part exhibiting a reflector function is formed from the bell mouth type pipe part. 
     Alternatively, a structure may be employed wherein the refrigerant outlet pipe and the refrigerant return pipe are formed as an integrated tubular pipe having a connection part therebetween, an opening as the first refrigerant inflow port is formed on a pipe wall of the refrigerant outlet pipe positioned above the connection part, and the part exhibiting a reflector function comprises a bevel part which extends from the connection part or the vicinity thereof toward an obliquely downward direction and which is enlarged in diameter as located at a lower position. 
     Alternatively, a structure may be employed wherein the refrigerant return pipe comprises a first bell mouth type pipe part which extends upwardly from the second refrigerant inversion part and which is enlarged in diameter as located at an upper position, and a second bell mouth type pipe part which is connected to an upper end of the first bell mouth type pipe part and which is contracted in diameter as located at an upper position, a lower end of the refrigerant outlet pipe is connected to an upper end of the refrigerant return pipe at a connection part to form an integrated pipe structure, an opening as the first refrigerant inflow port is formed on a pipe wall of the refrigerant outlet pipe positioned above the connection part, and the part exhibiting a reflector function is formed from the first bell mouth type pipe part. 
     Alternatively, a structure may be employed wherein the refrigerant return pipe comprises a tubular pipe part having a constant diameter which extends upwardly from the second refrigerant inversion part, a first bell mouth type pipe part which extends upwardly from an upper end of the tubular pipe part and which is enlarged in diameter as located at an upper position, and a second bell mouth type pipe part which is connected to an upper end of the first bell mouth type pipe part and which is contracted in diameter as located at an upper position, a lower end of the refrigerant outlet pipe is connected to an upper end of the refrigerant return pipe at a connection part to form an integrated pipe structure, an opening as the first refrigerant inflow port is formed on a pipe wall of the refrigerant outlet pipe positioned above the connection part, and the part exhibiting a reflector function is formed from the first bell mouth type pipe part. 
     The above-described refrigerant outlet pipe or refrigerant return pipe may be fixed relative to the tubular outer pipe at a predetermined figure and at a predetermined position by a certain manner. For example, a structure may be employed wherein at least the refrigerant return pipe is supported relative to the inner surface of the tubular outer pipe via a bracket at a condition where a path for refrigerant containing refrigeration machine oil is ensured. 
     It is preferred that the refrigeration machine oil separated by the oil separator and temporarily stored in the oil storage part according to the present invention is returned to a portion needing lubrication in the system, in particular, returned to a compressor, for example, a crank chamber in the compressor. For this, it is preferred that an oil return tube for returning refrigeration machine oil stored in the oil storage part to a compressor is connected to the oil separator. 
     Further, the position for disposing the oil separator according to the present invention is not particularly restricted as long as it is an exit side of a compressor, and for example, an embodiment can be employed wherein the oil separator is disposed between a compressor and a condenser in a refrigeration circuit having the compressor, the condenser, an expansion mechanism and an evaporator in this order. In this case, a structure may be employed wherein the oil separator is built in a header pipe of the condenser, and the external outflow port of the refrigerant outlet pipe is opened toward inside of the header pipe. 
     Further, the oil separator according to the present invention, in particular, its tubular outer pipe, can also be formed integrally with another device or a part of another device. For example, in case where the oil separator is built in a header pipe of the above-described condenser, a structure may be employed wherein the header pipe and the tubular outer pipe are formed integrally by extrusion molding. 
     Furthermore, although use, etc. of according to the present invention also is not particularly restricted, from the viewpoint that the oil separator is excellent in mounting property and space efficiency for disposition as well as in performance, it is particularly suitable to be provided in a refrigeration circuit of an air conditioning system for a vehicle. For example, even in case being mounted in an engine room, it can be mounted efficiently without causing a waste dead space. 
     Effect According to the Invention 
     Thus, according to the oil separator of the present invention, in the oil separator separating refrigeration machine oil and refrigerant basically by centrifugal separation, since the refrigerant inversion parts for inverting the flow direction of separated refrigerant in relation to the vertical direction are provided at two steps, the separated refrigerant can be discharged from both refrigerant inversion parts through the refrigerant outlet pipe and it can be effectively prevented by the part exhibiting a reflector function that the oil temporarily stored in the oil storage part at the bottom portion is returned into the separated refrigerant by splashing up and the like, an excellent separation performance capable of separating refrigeration machine oil and refrigerant with an extremely high efficiency can be exhibited. By the excellent separation performance, refrigeration machine oil can be efficiently circulated only to places necessary to be lubricated, and the rate of oil circulation can be effectively reduced as viewed from the whole of a refrigeration system connecting respective heat exchangers, etc. Therefore, the amount of oil enclosed in the system can be reduced, and the amount of oil circulation to a part, which basically does not require circulation of refrigeration machine oil, can be greatly reduced, thereby realizing improvement of performance of heat transfer and at respective heat exchangers and reduction of resistance of refrigerant flow in the refrigeration circuit, and further improving COP (coefficient of performance) as a whole. Further, since staying of oil at a portion, which basically does not need refrigeration machine oil, can also be reduced, improvement of the quality and reliability for durability of each portion can be expected. By improvement of these performances, in case where the oil separator according to the present invention is applied to an air conditioning system for a vehicle, it can contribute also to saving of fuel consumption of the vehicle. 
     Further, in the oil separator according to the present invention, because it is not necessary to provide a part enlarged in pipe diameter to the tubular outer pipe, a compact structure can be realized particularly by avoiding a large-sized configuration in the radial direction, and in case where the oil separator is mounted as a sole body, it can be mounted without causing a waste dead space, for example, along a part of another device, and therefore, it can be mounted at a good space efficiency. Further, because there is no part enlarged in pipe diameter in the tubular outer pipe, it becomes possible to incorporate it into a part of another device, for example, into a header pipe of a condenser with an integral structure, the mounting property can be further improved, and it may also become possible to make the whole of the system compact, facilitate the manufacture thereof, and reduce the cost. Such an excellent space efficiency of the oil separator according to the present invention, in case of applying it to an air conditioning system for a vehicle, may contribute to increase of design freedom of the vehicle, and further, to reduction of amount of material for a vehicle body, lightening in weight thereof, etc. 
    
    
     
       BRIEF EXPLANATION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an oil separator according to an embodiment of the present invention. 
         FIG. 2  is a schematic diagram of an oil separator according to another embodiment of the present invention. 
         FIG. 3  is a schematic diagram of an oil separator according to a further embodiment of the present invention. 
         FIG. 4  is a schematic diagram of an oil separator according to a still further embodiment of the present invention. 
         FIG. 5  is a schematic diagram of an oil separator according to a still further embodiment of the present invention. 
         FIG. 6  is a schematic diagram of an oil separator according to a still further embodiment of the present invention. 
         FIG. 7  is a systematic diagram of equipment of a refrigeration circuit showing an example of a position disposed with an oil separator according to the present invention. 
         FIG. 8  is a schematic partial diagram of a structure of an example wherein an oil separator according to the present invention is incorporated integrally into a header pipe of a condenser. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments of the present invention will be explained referring to figures. 
       FIG. 1  shows schematic structure and operation of an oil separator according to an embodiment of the present invention. In the figure, symbol  1  indicates an oil separator, the oil separator  1  separates discharged refrigerant from a compressor  2  (high-temperature and high-pressure gas refrigerant), which contains refrigeration machine oil, into refrigeration machine oil and refrigerant, and returns the separated refrigerant to, for example, a condenser disposed at a downstream side in a refrigeration circuit, and returns the separated refrigeration machine oil into, for example, a crank case of compressor  2  through an oil return tube  3 . Oil separator  1  has a tubular outer pipe  4  which is disposed on a outlet side of compressor  2  so as to extend in a vertical direction substantially at a constant diameter and at a configuration of a straight pipe, and an inlet pipe  6  provided at an upper part of the tubular outer pipe  4  for introducing refrigerant containing refrigeration machine oil, discharged from compressor  2 , into the tubular outer pipe  4  in such a manner as to produce a downward helical flow  5  of the refrigerant containing refrigeration machine oil along an inner surface of the tubular outer pipe  4 . The refrigerant introduction angle of this inlet pipe  6  relative to tubular outer pipe  4  is set at an angle that does not decrease the speed of the refrigerant, which has been introduced into tubular outer pipe  4 , in the circumferential direction of the tubular outer pipe so much, for example, set at an angle close to the tangential direction of the inner circumferential surface of tubular outer pipe  4 . The refrigerant containing refrigeration machine oil introduced into tubular outer pipe  4  flows down along the inner surface of tubular outer pipe  4  while depicting helical flow  5 , and at that time, a part of refrigeration machine oil greater in mass is centrifugally separated from refrigerant, and the separated refrigeration machine oil flows downward moving on and along the inner surface of tubular outer pipe  4  by its self-weight. 
     This oil separator  1  further has a refrigerant outlet pipe  11  which has an external outflow port  7  at an upper end side for flowing out the separated refrigerant to outside of tubular outer pipe  4 , has a section extending in the axial direction of tubular outer pipe  4  at a central position of tubular outer pipe  4 , and has a first refrigerant inflow port  10  at a lower end side of the section for flowing in refrigerant therein, which has been separated from refrigerant containing refrigeration machine oil having flowed down in the helical flow  5  and the flow direction of which has been inverted in relation to vertical direction at a first refrigerant inversion part  8 , and has a refrigerant return pipe  16  which extends in an axial direction of tubular outer pipe  4  at a central position of tubular outer pipe  4 , below this refrigerant outlet pipe  11 , has a refrigerant communication port  12  at an upper end side for being confronted with or connected to a lower end of refrigerant outlet pipe  11  (in this depicted example, being confronted at a gap), and has a second refrigerant inflow port  15  at a lower end side for flowing in refrigerant therein, which has been separated from refrigerant containing refrigeration machine oil having flowed down in the helical flow  5  and the flow direction of which has been inverted in relation to vertical direction at a second refrigerant inversion part  13 . The above-described external outflow port  7  of refrigerant outlet pipe  11  is formed at an end of the upper portion of refrigerant outlet pipe  11  which is formed in a curved pipe. Further, oil separator  1  has an oil storage part  17 , which is formed at a bottom portion of tubular outer pipe  4 , capable of temporarily storing refrigeration machine oil separated from refrigerant. 
     Then, in this oil separator  1 , a part exhibiting a reflector function  18  for preventing refrigeration machine oil stored in oil storage part  17  from flowing out into refrigerant outlet pipe  11  is provided between refrigerant return pipe  16  and the inner surface of tubular outer pipe  4 . In this embodiment, part exhibiting a reflector function  18  is formed at an upper portion side of refrigerant return pipe  16  and formed as a bell mouth type pipe which is enlarged in diameter as located at an upper position. Where, in  FIG. 1 , symbol  20  indicates a support bracket for fixing refrigerant outlet pipe  11  at a predetermined position relative to the inner surface of tubular outer pipe  4 , and symbol  21  indicates a support bracket for fixing refrigerant return pipe  16  at a predetermined position relative to the inner surface of tubular outer pipe  4 . 
     In oil separator  1  according to this embodiment constituted as described above, since two refrigerant inversion parts of first refrigerant inversion part  8  and second refrigerant inversion part  13  are provided in the downflow direction of helical flow  5  of refrigerant containing refrigeration machine oil and refrigerant separated and inverted in order at the two-step refrigerant inversion is introduced in the external discharge direction through refrigerant outlet pipe  11 , the efficiency of separation can be greatly improved as compared with a conventional single-step separation. Further, by the structure wherein part exhibiting a reflector function  18  is provided between first refrigerant inversion part  8  and second refrigerant inversion part  13 , it can be prevented by the reflector effect due to the part exhibiting a reflector function  13  that the refrigeration machine oil temporarily stored in oil storage part  17  flows out into refrigerant outlet pipe  11  through first refrigerant inflow port  10  by splashing up, etc. of refrigerant in the upward direction due to the disturbance, etc. of refrigerant at second refrigerant inversion part  13 . The return flow of the oil returned again to oil storage part  17  by this reflector effect is indicated by symbol  19  in  FIG. 1 . Further, because the oil splashed up into refrigerant return pipe  16  is also weakened in refrigerant flow speed in the upper diameter-enlarged pipe portion forming this part exhibiting a reflector function  13 , refrigeration machine oil great in mass is liable to be returned again toward oil storage part  17  at the bottom portion through the inside of refrigerant return pipe  16 . Thus, since oil return into the separated refrigerant due to oil splashing up, etc. can be prevented, the efficiency of separation can be further improved. 
     Further, because this part exhibiting a reflector function  18  also functions for temporarily contracting the cross-sectional area of flow path with respect to the downflow of helical flow  5  of the refrigerant containing refrigeration machine oil as shown in the figure, it can be achieved to improve the inversion and separation performance of refrigerant at first refrigerant inversion part  8  positioned at an upstream side of part exhibiting a reflector function  18 , and because the flow speed is temporarily increased by the temporary contraction of the cross-sectional area of flow path, the centrifugal separation performance due to the helical flow at a downstream side of part exhibiting a reflector function  18  is improved, and further, the flow speed is rapidly changed by the enlargement in cross-sectional area of flow path after the temporary contraction of the cross-sectional area of flow path, and therefore, it may be also expected to improve the inversion and separation performance of refrigerant at second refrigerant inversion part  13 . Therefore, the efficiency for separation as the whole of oil separator  1  can be greatly improved, as compared with a conventional structure at a single step without a part exhibiting a reflector function. 
     Further, because of the separation due to the two-step refrigerant inversion at first refrigerant inversion part  8  and second refrigerant inversion part  13 , since the resistance with respect to refrigerant inflow into the discharge path at the time of inversion separation at each refrigerant inversion part is suppressed small, as compared with a conventional one-step case, the resistance in flow path at this part at the time of discharge can be reduced, and consequently, reduction of the resistance in flow path and the pressure loss as the whole of the oil separator becomes possible. Further, as aforementioned, by the discharge operation of the refrigerant separated at first refrigerant inversion part  8  through refrigerant outlet pipe  11 , suction operation from refrigerant return pipe  16  disposed therebelow at a confronting state is induced, and inducing effect from second refrigerant inflow port  15  of refrigerant return pipe  16 , of the refrigerant  14  separated at second refrigerant inversion part  13 , can also be expected. As a result, as the whole of oil separator  1 , an efficient discharge of separated refrigerant becomes possible, and further reduction of resistance in refrigerant flow path and pressure loss becomes possible. 
     Further, because tubular outer pipe  4  is formed as a straight pipe shape with a substantially constant diameter and first refrigerant inversion part  8 , second refrigerant inversion part  13  and part exhibiting a reflector function  18  are formed in the straight pipe-shape tubular outer pipe  4 , it is not necessary to provide a diameter-enlarged pipe portion to tubular outer pipe  4  defining the outline of the oil separator, in particular, a structure compact in the radial direction and good in space efficiency can be realized, and the mounting property into a place limited in space (for example, into an engine room of a vehicle) can be improved. 
     In the oil separator according to the present invention, various structures can be employed for the refrigerant return pipe, the part exhibiting a reflector function, and the connection structure between the refrigerant outlet pipe and the refrigerant return pipe. Hereinafter, some structural examples thereof will be shown. 
     In oil separator  31  shown in  FIG. 2 , although inlet pipe  33 , refrigerant outlet pipe  34  and refrigerant return pipe  35  are provided relatively to tubular outer pipe  32  similarly in the above-described embodiment, the refrigerant return pipe  35  is formed as constant-diameter tubular pipe extending upwardly from second refrigerant inversion part  36 , and a part exhibiting a reflector function  37  is formed as a bevel part which extends from an upper end of this tubular pipe toward an obliquely downward direction and which is enlarged in diameter as located at a lower position. In such a part exhibiting a reflector function  37  formed as a bevel part, the inflow of the oil splashed up from a lower position to a portion around refrigerant return pipe  35  can be prevented efficiently. 
     In oil separator  41  shown in  FIG. 3 , although inlet pipe  43 , refrigerant outlet pipe  44  and refrigerant return pipe  45  are provided relatively to tubular outer pipe  42  similarly in the aforementioned embodiment, substantially the entire length of the refrigerant return pipe  45  comprises a bell mouth type pipe which extends upwardly from a second refrigerant inversion part  46  and which is enlarged in diameter as located at an upper position, and the part exhibiting a reflector function is formed from the bell mouth type pipe. Namely, the refrigerant return pipe  45  and the part exhibiting a reflector function are formed as an identical pipe. In the structure of such a part exhibiting a reflector function, the reflector effect can be exhibited over a relatively long zone in the vertical direction. 
     In oil separator  51  shown in  FIG. 4 , although an inlet pipe (omitted in the figure), refrigerant outlet pipe  53  and refrigerant return pipe  54  are provided relatively to tubular outer pipe  52  similarly in the aforementioned embodiment, refrigerant outlet pipe  53  and refrigerant return pipe  54  are formed as an integrated tubular pipe having a connection part  55  therebetween, and an opening  56  as the first refrigerant inflow port is formed on a pipe wall of refrigerant outlet pipe  53  positioned above this connection part  55 . Then, a part exhibiting a reflector function  57  is formed as a structure comprising a bevel part which extends from the connection part  55  or the vicinity thereof toward an obliquely downward direction and which is enlarged in diameter as located at a lower position. Symbol  58  indicates a support bracket for fixing the above-described integrated tubular pipe at a predetermined position relatively to the inner surface of tubular outer pipe  52 . Because refrigerant outlet pipe  53  and refrigerant return pipe  54  are formed as an integrated tubular pipe, supporting by support bracket  58  becomes easy, and the number of support bracket s  58  may be small. 
     In oil separator  61  shown in  FIG. 5 , although an inlet pipe (omitted in the figure), refrigerant outlet pipe  63  and refrigerant return pipe  64  are provided relatively to tubular outer pipe  62  similarly in the aforementioned embodiment, refrigerant return pipe  64  comprises a first bell mouth type pipe part  66  which extends upwardly from second refrigerant inversion part  65  and which is enlarged in diameter as located at an upper position, and a second bell mouth type pipe part  67  which is connected to an upper end of the first bell mouth type pipe part  66  and which is contracted in diameter as located at an upper position, and a lower end of refrigerant outlet pipe  63  is connected to an upper end of refrigerant return pipe  64  at a connection part  68  to form an integrated pipe structure. An opening  69  as the first refrigerant inflow port is formed on a pipe wall of refrigerant outlet pipe  63  positioned above this connection part  68 . Then, the part exhibiting a reflector function is formed from the above-described first bell mouth type pipe part  66 . Refrigerant outlet pipe  63  and refrigerant return pipe  64  formed as an integrated tubular pipe are fixed at predetermined positions relatively to the inner surface of tubular outer pipe  62  by support brackets  70 . In such a structure, the part exhibiting a reflector function can be formed by first bell mouth type pipe part  66  over a relatively long zone, and by second bell mouth type pipe part  67 , it becomes possible to perform the refrigerant inversion at the first refrigerant inversion part more smoothly and to promote the flow path contraction effect relative to the downward helical flow, and therefore, a more smooth as a whole can be expected. 
       FIG. 6  depicts an oil separator  71  according to a modification of the structure shown in  FIG. 5 , as compared with the structure shown in  FIG. 5 , refrigerant return pipe  72  comprises a tubular pipe part  74  having a constant diameter which extends upwardly from second refrigerant inversion part  73 , a first bell mouth type pipe part  75  which extends upwardly from an upper end of the tubular pipe part  74  and which is enlarged in diameter as located at an upper position, and a second bell mouth type pipe part  76  which is connected to an upper end of the first bell mouth type pipe part  75  and which is contracted in diameter as located at an upper position. Tubular outer pipe  77 , an inlet pipe (omitted in the figure), refrigerant outlet pipe  78 , opening  79  and support brackets  80  are substantially the same in structure as those shown in  FIG. 5 . 
     As aforementioned, the position for disposing the oil separator according to the present invention is not particularly restricted as long as it is an exit side of a compressor, and for example, as shown in  FIG. 7 , an oil separator  86  can be disposed between a compressor  81  and a condenser  82  in a refrigeration circuit  85  having the compressor  81 , the condenser  82 , an expansion mechanism  83  and an evaporator  84  in this order. 
     In this case, in particular, a structure can be employed wherein oil separator  86  is built in a header pipe of condenser  82 , and the external outflow port of the refrigerant outlet pipe is opened toward the inside of the header pipe. Further in this case, for example, as shown in  FIG. 8 , it is possible to incorporate an oil separator  91  into a header pipe  93  of a condenser  92  and to form the header pipe  93  and a tubular outer pipe  94  of the oil separator  91  integrally, in particular, to integrally form by extrusion molding. In  FIG. 8 , symbol  95  indicates heat exchange tubes of condenser  92  connected to header pipe  93 , symbol  96  indicates a lid portion of header pipe  93 , symbol  97  indicates an inlet pipe of oil separator  91 , and symbol  98  indicates a refrigerant outlet pipe of oil separator  91 , respectively, and a part of the integrally formed tubular outer pipe  94  forms a partition wall  99  between oil separator  91  and the tube-side inside of header pipe  93 . In such a structure, a desired oil separator  91  can be disposed compactly in a refrigeration circuit without making the whole of the refrigeration circuit particularly large-sized. 
     INDUSTRIAL APPLICATIONS OF THE INVENTION 
     The oil separator according to the present invention can be applied to any use for separating refrigeration machine oil from refrigerant discharged from a compressor, and in particular, it is suitable to be disposed in a refrigeration circuit, especially, between a compressor and a condenser in a refrigeration circuit of an air conditioning system for a vehicle. 
     EXPLANATION OF SYMBOLS 
     
         
           1 ,  31 ,  41 ,  51 ,  61 ,  71 ,  86 ,  91 : oil separator 
           2 ,  81 : compressor 
           3 : oil return tube 
           4 ,  32 ,  42 ,  52 ,  62 ,  77 ,  94 : tubular outer pipe 
           5 : helical flow 
           6 ,  33 ,  43 ,  97 : inlet pipe 
           7 : external outflow port 
           8 : first refrigerant inversion part 
           9 : inverted refrigerant 
           10 : first refrigerant inflow port 
           11 ,  34 ,  44 ,  53 ,  63 ,  78 ,  98 : refrigerant outlet pipe 
           12 : refrigerant communication port 
           13 ,  36 ,  46 ,  65 ,  73 : second refrigerant inversion part 
           14 : inverted refrigerant 
           15 : second refrigerant inflow port 
           16 ,  35 ,  45 ,  54 ,  64 ,  72 : refrigerant return pipe 
           17 : oil storage part 
           18 ,  37 ,  57 : part exhibiting a reflector function 
           19 : return flow of oil 
           20 ,  21 ,  58 ,  70 ,  80 : support bracket 
           55 ,  68 : connection part 
           56 ,  69 ,  79 : opening 
           66 ,  75 : first bell mouth type pipe part 
           67 ,  76 : second bell mouth type pipe part 
           74 : tubular pipe part having a constant diameter 
           82 ,  92 : condenser 
           83 : expansion mechanism 
           84 : evaporator 
           85 : refrigeration circuit 
           93 : header pipe 
           95 : heat exchange tube 
           96 : lid portion of header pipe 
           99 : partition wall