Abstract:
The invention relates to an air conditioning unit with a coolant circuit which consists of a compressor, an evaporator, a collector located at the low pressure side between the evaporator and the compressor and an inner heat transfer unit with a beat transfer channel located at the high pressure side and a low pressure side beat transfer channel. According to the invention, the inner heat transfer unit has an at least segmentally spiraling and/or spiral-shaped steps between the outer and inner pipe of a coaxial pipe system. Additionally or alternatively, the inner heat transfer unit contains a multiple channel line which surrounds the collector in a spiral fashion and/or in which a low pressure side pipe longitudinal channel has a first segment which exits into said collector housing and a second segment which exits out of the said collector housing in addition to a high-pressure side pipe longitudinal channel which traverses the collector housing or leads into a first segment in a high-pressure execution chamber of said collector housing and a second segment leads out of the said chamber. Said invention can be used as a CO 2 -air conditioning unit in vehicles.

Description:
The invention relates to an air-conditioning system with a refrigerant circuit which comprises an evaporator, a compressor conveying the refrigerant from a low-pressure side to a high-pressure side, a header arranged on the low-pressure side between the evaporator and the compressor and an internal heat exchanger which has a high-pressure-side heat exchanger duct and a low-pressure-side heat exchanger duct which is in thermal contact with the latter. 
     Air-conditioning systems of this type are used, in particular, in motor vehicles, for example in the form of CO 2  air-conditioning systems. The internal heat exchanger serves for transmitting heat from the refrigerant on the high-pressure side to the refrigerant on the low pressure side, with the result that what is known as the performance number, that is to say the ratio of the refrigerating capacity and the drive power of the air-conditioning system, can be markedly increased. 
     An air-conditioning system of this type is disclosed in the publicly distributed publication DE 196 35 454 A1. There, the internal heat exchanger is integrated, together with the header, into a structural unit by being accommodated in the interior of a header housing, for example in the form of a flat-tube spiral with turns spaced from one another. 
     It is known, furthermore, to use as an internal heat exchanger for an air-conditioning system a coaxial tube conduit with two fluid-separated tube longitudinal ducts which are in thermal contact with one another, in order to subcool the high-pressure-side refrigerant upstream of an expansion valve by the transmission of heat to the low-pressure-side refrigerant. The laid-open publication DE 1 208 314 describes a coaxial tube conduit which serves this purpose and in which an inner tube is surrounded concentrically by an outer tube and is provided on the inside with a longitudinal ribbing increasing the heat transmission surface. A wire screw may be introduced between the outer tube and the inner tube in order to lengthen the flow path effective for heat transmission. Inner-tube configurations are also indicated there as known, in which the inner tube is folded in a star-shaped manner or in which a sheet-metal helix for generating a swirl flow is inserted into the inner tube. 
     An air-conditioning system for a motor vehicle is also known, in which an internal heat exchanger is combined with an evaporator and with an expansion valve to form an integral structural unit. However, such a combination of the internal heat exchanger combining the internal heat exchanger in this way onto or into the evaporator often entails a relatively high construction space requirement, which, particularly under the confined conditions of installation of motor vehicles, may lead to difficulties. 
     In the older German patent application No. 199 03 833.3 which has not already been published, an integrated header/heat-exchanger structural unit is disclosed, in which the internal heat exchanger is formed by a coiled coaxial tube conduit which is received in the header housing. 
     The technical problem on which the invention is based is to provide an air-conditioning system of the type initially mentioned, with an internal heat exchanger which can be manufactured relatively simply and, for a given heat transmission capacity, requires relatively little additional construction space. 
     The invention solves this problem by the provision of an air-conditioning system having the features of claim 1, 3 or 4. 
     According to one embodiment of the present invention, an air-conditioning system is provided with an internal heat exchanger that contains, in particular, a coaxial tube conduit which has helical webs between an outer tube and an inner tube and/or which is coiled overall at least in portions. The helical webs are integrally formed on the outer tube and/or the inner tube and can therefore be implemented relatively simply in production terms. By virtue of their helical shape, for a given construction length of the coaxial tube conduit, they lengthen the flow path for the refrigerant, for example the low-pressure-side refrigerant, which flows through between the outer tube and the inner tube and which is in thermal contact with the refrigerant, for example the high-pressure-side refrigerant, led through the inner tube. Additionally or alternatively to this measure, the coaxial tube conduit may have a coiled design, with the result that the construction space length required can be kept markedly smaller than the flow path length effective for heat transmission. At the same time, the low-pressure-side heat exchanger duct forms a refrigerant circuit portion between the evaporator and the header and/or between the header and the compressor. 
     According to another embodiment of the present invention, the coaxial tube conduit is formed by an extruded inner tube with outer webs, which is pushed into an outer tube, or by an extruded outer tube with inner webs, into which the inner tube is pushed, or by a tube extruded in one piece and having integrated webs between the inner and the outer tube. 
     According to another embodiment of the present invention, the extent of the internal heat exchanger formed by a multiduct tube conduit extends, on the low-pressure side, on both sides of the header, for which purpose the low-pressure-side tube longitudinal duct has a portion issuing into a housing of the header and a portion issuing out of said housing, while the high-pressure-side tube longitudinal duct crosses the header housing as a continuous duct or issues with a first portion into a high-pressure leadthrough space formed within the header housing and issues with a second portion out of said high-pressure leadthrough space. Depending on the configuration within the header housing, there, the issuing-in and/or issuing-out low-pressure-side tube longitudinal duct is in thermal contact with the high-pressure-side tube longitudinal duct or the high-pressure leadthrough space, so that the internal heat exchanger consequently also extends at least partially within the header housing. 
     According to another embodiment of the present invention, the internal heat exchanger contains a coiled multiduct tube conduit which surrounds the header. In other words, in this case, the header is accommodated in the tube helix of the internal heat exchanger, thus keeping the construction space requirement of the air-conditioning system low. 
     According to another embodiment of the present invention, the outside of the header is provided with a screw-shaped profile corresponding to the surround multiduct tube conduit helix, so that the latter comes to bear with a form fit against the outside of the header in a guided manner. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Advantageous embodiments of the invention are illustrated in the drawings and are described below. In the drawings: 
     FIG. 1 shows a block diagram of an air-conditioning system having a refrigerant circuit with an internal heat exchanger in the form of a multiduct tube conduit, 
     FIGS. 2 to  5  show diagrammatic illustrations of possible helical shapes for the multiduct tube conduit of the air-conditioning system of FIG. 1, 
     FIGS. 6 to  10  show cross sections of various embodiments of the multiduct tube conduit as a coaxial tube conduit, 
     FIG. 11 shows a longitudinal sectional view of a header region of the refrigerant circuit of FIG. 1 with a led-through high-pressure conduit, 
     FIG. 12 shows a longitudinal sectional view corresponding to that of FIG. 11, but for a variant with a high-pressure leadthrough space in the header, 
     FIG. 13 shows a perspective view of a header with a helically surrounding coaxial tube conduit of an internal heat exchanger for an air-conditioning system in the manner of FIG. 1, and 
     FIG. 14 shows a diagrammatic longitudinal sectional view of a variant of the combination of header and internal heat exchanger according to FIG. 13 with a screw-shaped header profile. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows diagrammatically, as a block diagram, the set-up of an air-conditioning system, such as can be used, for example, in a motor vehicle. In the associated refrigerant circuit are located, as is customary, a compressor  1 , a condenser  2  which follows the latter on the high-pressure side and, for example when CO 2  is used as refrigerant, is generally designated more precisely as a gas cooler, an expansion valve  3  located downstream of said condenser, an evaporator  4  following said expansion valve in the refrigerant flow direction and a header  5  arranged on the low-pressure side between the evaporator  4  and the compressor  1 . Insofar as the high-pressure-side refrigerant conduit and the low-pressure-side refrigerant conduit are reproduced in FIG. 1 by closely adjacent lines, one or more of these circuit portions may, depending on the application, be implemented by a multiduct tube conduit forming an internal heat exchanger. 
     The internal heat exchanger consequently contains a first portion  6   a , which forms on the low-pressure side at least part of the refrigerant conduit from the evaporator  4  to the header  5 , and/or a second portion  6   b , which forms on the low-pressure side at least part of the refrigerant conduit from the header  5  to the compressor  1  and on the high-pressure side, like the first portion  6   a , at least part of the refrigerant conduit from the condenser/gas cooler  2  to the expansion valve  3 , and/or a third portion  6   c , which forms on the high-pressure side at least part of the refrigerant conduit from the compressor  1  to the condenser/gas cooler  2  and on the low-pressure side, like the second portion  6   b , at least part of the refrigerant conduit from the header  5  to the compressor  1 . In a variant indicated by broken lines, the high-pressure-side refrigerant conduit bypasses the header  5  and leads, without renewed thermal conduct with the low-pressure side, to the expansion valve  3 , that is to say, in this case, the first portion  6   a  of the internal head exchanger is dispensed with. In a similar way, another of the three internal heat exchanger portions  6   a ,  6   b ,  6   c  or two of them may be dispensed with. 
     FIGS. 2 to  5  outline some possible helical embodiments of the multiduct tube conduit which are capable of being used to form the internal heat exchanger portions  6   a ,  6   b ,  6   c  so as to save construction space. In particular, FIG. 2 shows a multiduct tube conduit  7  which is wound in a corresponding portion to form a helix  7   a  with a rectilinear helix longitudinal axis. FIG. 3 shows a multiduct tube conduit  8  which has a portion bent into a U-bend  8   a . FIG. 4 shows a multiduct tube conduit  9  with a portion  9   a  coiled to form a loop. FIG. 5 shows a multiduct tube conduit  10  with two helical portions  10   a ,  10   b  with helix longitudinal axes perpendicular to one another. 
     FIGS. 6 to  10  show cross-sectional views of various embodiments of the multiduct tube conduit forming the internal heat exchanger, as a coaxial tube conduit. In particular, FIG. 6 illustrates an internal heat exchanger in the form of a coaxial tube which consists of an extruded inner tube  11  with four helically running longitudinal webs  12   a ,  12   b ,  12   c ,  12   d  integrally formed on the outside at an equidistant angular interval, said inner tube being pushed into an associated outer tube  13 . In the exemplary embodiment of FIG. 7, the coaxial tube conduit for the internal heat exchanger consists of an extruded outer tube  14 , on the inside of which four helically running longitudinal webs  15   a  to  15   d  arranged at an equidistant angular interval are integrally formed and into which an associated inner tube  16  is pushed. FIG. 8 shows a coaxial tube  17  which can be used as an internal heat exchanger and is manufactured, extruded, as a one-piece component, an inner tube part  18  and an outer tube part  19  being connected to one another via four longitudinal webs  20   a  to  20   d  arranged at an equidistant angular interval and running helically in the tube longitudinal direction. In all three examples of FIGS. 6 to  8 , the helical run of the longitudinal webs may be brought about, during the extrusion manufacturing operation, by appropriate twisting about the longitudinal axis of the inner tube  11  as regards FIG. 6, of the outer tube  14  as regards FIG. 7 or of the entire coaxial tube  17  as regards FIG. 8, and the helix pitch can be set variably in a desired way. By the choice of the equidistant angular intervals of the webs, the annular space between the outer and the inner tube part is divided into individual ducts with an equal flow cross section. 
     FIG. 9 shows a coaxial tube configuration for the internal heat exchanger, in which an inner tube  21  having a rounded star-shaped tube wall cross section is pushed into an outer tube  22 . In the exemplary embodiment of FIG. 10, the coaxial tube conduit for the internal heat exchanger consists of an inner tube  23 , an outer tube  24  and a corrugated rib profile  25  inserted between the inner tube  23  and the outer tube  24 . 
     In all the examples of FIGS. 6 to  10 , the respective coaxial tube conduit contains a one-part inner tube longitudinal duct formed by the surrounding inner tube and a multipart outer tube longitudinal duct which is formed by the interspace between the inner tube and the outer tube and which is divided into a plurality of parallel outer longitudinal ducts by the webs or the inner tube wall profile or the corrugated rib profile. A helical run of the separating elements between the individual outer longitudinal ducts lengthens the flow path for the refrigerant led through there, as compared with the tube length, and thereby intensifies thermal contact between this refrigerant stream and the refrigerant stream led through the inner tube. In addition, as explained above with regard to FIGS. 2 to  5 , the coaxial tube conduit may be coiled as a whole partially or completely, so that its constructional length can be shortened and it can thereby be introduced more easily in confined construction spaces. Consequently, by the internal heat exchanger being implemented as a multiduct tube conduit, only a single multiduct tube needs to be bent in order to achieve a correspondingly bent space-saving flow routing both for the high-pressure-side and for the low-pressure-side heat exchanger duct of the internal heat exchanger. 
     It goes without saying that, in addition to the embodiments shown in FIGS. 6 to  10 , further multiduct tube configurations are possible, for example those in which there are in each case for the high-pressure-side and the low-pressure-side refrigerant a plurality of individual tube ducts which, moreover, do not necessarily have to be coaxial, but, for example, may also be arranged alternately next to one another. Alternatively, instead of the high-pressure-side and low-pressure-side refrigerant being routed into the internal heat exchanger portions  6   a ,  6   b ,  6   c  as indicated by arrows in FIG. 1, the routing of said refrigerant may be provided in cocurrent for all or only some of the internal heat exchanger portions  6   a ,  6   b ,  6   c . Where the coaxial tube conduit is concerned, the high-pressure-side refrigerant is preferably routed in the inner tube, while the low-pressure-side refrigerant is routed in the annular space between the inner and the outer tube, but, alternatively, the routing of the high-pressure-side refrigerant in the outer annular space and the routing of the low-pressure-side refrigerant in the inner tube are also possible. 
     FIG. 11 shows an exemplary embodiment in which the header  5  is followed on each of the two sides by a portion of the internal heat exchanger in the coaxial tube form of construction and, at the same time, a high-pressure-side conduit crosses a header housing  5   a  closing off the header  5  outwardly. For this purpose, the header housing  5   a  has located in it a header bowl  26 , into which a first coaxial tube conduit  27  led through the header housing  5   a  from above leads and terminates with its outer tube  27   a  at a short distance above the bowl bottom  26   a , into which one or more oil suction-extraction bores  28  are introduced. By contrast, the inner tube  27   b  of the coaxial tube conduit  27  is led further on, fluid-tight, through a corresponding orifice in the bowl bottom  26   a  and is led out of the header housing  5   a  downwardly. It forms, there, the inner tube of a second coaxial tube conduit  29 , the outer tube of which issues, fluid-tight, into the bottom region of the header housing  5   a  below the header bowl  26 . 
     In this way, the first coaxial tube conduit  27  forms the first internal heat exchanger portion  6   a  and the second coaxial tube conduit  29  the second internal heat exchanger  6   b  of FIG.  1 . The low-pressure-side refrigerant  32  coming from the evaporator passes, via the outer annular duct of the first coaxial tube conduit  27 , into the header bowl  26 , from where, as indicated by the arrows, the collected refrigerant is sucked by the compressor suction action into the region between the header bowl  26  and the header housing  5   a  and from there into the header bottom region and the outer annular duct of the second coaxial tube conduit  29 , in order, in said outer annular duct, to arrive directly or via the condenser/gas cooler at the compressor. The high-pressure-side refrigerant  31  coming from the condenser/gas cooler crosses the header  5  centrally in the inner tube  27   b  led through uninterruptedly and, at the same time, within the header housing  5   a , is also in thermal contact, over the greatest part of the respective flow length, with the low-pressure-side refrigerant coming from the evaporator. Alternatively to the countercurrent routing shown, a cocurrent routing of the high-pressure-side refrigerant  31  and low-pressure-side refrigerant  32  is possible. 
     FIG. 12 shows a variant of the example of FIG. 11, in which an intermediate casing  33  is introduced between an outer header housing  5   c  and an inner heading bowl  26   a . This intermediate casing closes off the header bowl  26   a  upwardly, with clearance, in a fluid-tight manner, a low-pressure inner tube  34  crossing this cover region of the intermediate casing  33  in a fluid-tight manner and terminating above the header bowl bottom, into which at least one oil suction-extraction bore  35  is introduced. The low-pressure inner tube  34  thus serves for feeding the low-pressure-side refrigerant  41  coming from the evaporator into the header bowl  26   a . Said low-pressure inner tube is surrounded outwardly from the top side of the header housing  5   c , so as to form a corresponding coaxial tube conduit  37 , by an outer tube  36  which is connected, fluid-tight, to the top side of the header housing  5   c  and issues out there. The intermediate casing  33  narrows downwardly, in the form of a bottleneck, into a further outlet-side low-pressure inner tube  38 .which emerges from the header housing  5   c  on the underside of the latter and is then surrounded by an associated outer tube  39 , so as to form a further coaxial tube conduit  40 , this outer tube  39  itself being secured, fluid-tight, to the bottom of the header housing  5   c  and issuing in there. 
     Consequently, in this exemplary embodiment, the first coaxial tube conduit  37  again forms the first internal heat exchanger portion and the other coaxial tube conduit  40  the second internal heat exchanger portion  6   b  of FIG.  1 . In this case, at the same time, the low-pressure-side refrigerant  41  coming from the evaporator flows through the inner tube  34  of the associated coaxial tube conduit  37  into the header bowl  26   a  and from there is sucked, via the annular space between the header bowl  26   a  and the intermediate casing  33 , out of the header housing  5   c  into the inner tube  38  of the other coaxial tube conduit  40 , in order to arrive from there directly or via the condenser/gas cooler at the compressor. In countercurrent to this, the high-pressure-side refrigerant  42  passes, via the annular duct of the lower coaxial tube conduit  40  in FIG. 12, into a high-pressure leadthrough space  43  which is formed in the header by the header housing  5   c  as an outer boundary and by the intermediate casing  33  as an inner boundary. After crossing the high-pressure leadthrough space  43 , the high-pressure-side refrigerant  42  leaves the header housing  5   c  upwardly via the annular duct of the coaxial tube conduit  37  following there. Consequently, via the intermediate casing  33 , the high-pressure-side refrigerant is in thermal contact, even along its flow path through the high-pressure leadthrough space  43  of the header, with the low-pressure-side refrigerant  41 . 
     FIG. 13 shows an exemplary embodiment in which a helically wound coaxial tube conduit  44  serves as an internal heat exchanger. A header  5   b  of cylindrical form of construction is arranged in a space-saving way in the interior of the coaxial tube helix  44 . High-pressure-side refrigerant  45  is fed, on end face of the coaxial tube helix  44 , to the inner tube duct of the latter and leaves this correspondingly on the other end face of the coaxial tube helix  44 . Low-pressure-side refrigerant  46  coming from the evaporator is fed to the header  5   d  from above. Under the suction action of the compressor, it is sucked from there, via a radial connection piece, not to be seen in FIG. 13, at the upper end of the coaxial tube helix  44 , into the outer annular space of the latter. For this purpose, this connection piece makes a fluid connection between the upper header region and the outer annular space of the coaxial tube helix  44  in the latter&#39;s upper end region located there. After crossing the outer annular space of the coaxial tube helix  44 , the refrigerant sucked out of the header  5   d  leaves the internal heat exchanger portion formed by the coaxial tube helix  44  via a further radial connection piece  47  which is formed on the lower end region of the coaxial tube helix  44  in fluid connection with the outer annular space of the latter. The outer annular space is closed on each end face. The coaxial tube helix  44  can thus serve as the second internal heat exchanger portion  6   b  of the air-conditioning system of FIG.  1 . 
     FIG. 14 shows diagrammatically a variant of the exemplary embodiment of FIG.  13 . In this modification, a cylindrical header  5   e  is provided on the outside of its housing with a screw-shaped profiling  48  which serves as a guide groove for a conformally inserted coaxial tube helix  49  which, guided in this way, surrounds the outer casing of the header  5   e . In this case, the lower part of the coaxial tube helix  49  is omitted in FIG. 14, so that the screw-shaped profiling  48  of the header  5   e  can be seen. This exemplary embodiment otherwise corresponds in set-up and functioning to that of FIG.  13 . 
     The embodiments described above in detail show that the invention provides an air-conditioning system which has an efficiency-increasing internal heat exchanger and at the same time requires relatively little installation space by the internal heat exchanger being formed by a multiduct tube conduit, of which the low-pressure-side heat exchanger duct lies upstream and/or downstream of a header in the refrigerant flow direction and, if required, may also extend into the header, and/or by being formed by a coaxial tube conduit, which is coiled overall and/or has coiled webs or separating elements between the outer and the inner tube part, so that the flow path for the tube ducts located between the outer and the inner tube part is lengthened, as compared with the longitudinal extent of the coaxial tube. The invention can be applied, in particular, to CO 2  air-conditioning systems of motor vehicles. Since the header, on the one hand, and the internal heat exchanger, on the other hand, form separate components of the air-conditioning system according to the invention, both can be adapted independently of one another to the vehicle present in each case. The header can be designed with a comparatively small volume due to the presence of the internal heat exchanger. What is known as the bar/liter product can thereby be reduced, with the result that the stability of the header container under high pressures is improved.