Abstract:
The present invention relates to a soldered flat tube for condensers and/or for evaporators in air-conditioning systems, in particular in motor vehicles, which can be produced by deformation of endless aluminum sheet-metal strips, has two narrow sides and two wide sides and also has inner passages with a hydraulic diameter which is greater than or equal to 0.254 mm, and the flat tube has a tube wall thickness of less than 0.25 mm, wherein both narrow sides are reinforced by having at least double the thickness of the remaining tube wall thickness.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Priority is hereby claimed to German Patent Application No. DE 10 2006 054 814.0, filed Nov. 22, 2006, the entire contents of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a soldered flat tube for condensers and/or evaporators in air-conditioning systems, and more particularly, to tubes for condensers and/or evaporator in motor vehicles. The tubes can be produced by deformation of one or more aluminum-containing sheet-metal strips, having two narrow sides and two wide sides. The tubes can include inner passages with a hydraulic diameter which is greater than or equal to 0.254 mm, and can have a tube wall thickness of less than 0.25 mm. 
       SUMMARY 
       [0003]    Soldered flat tubes for condensers are known from EP 273 164 A1. Flat tubes with inner passage hydraulic diameters in the range from 0.381-1.778 mm are nowadays standard equipment for what are known as parallel-flow condensers.  FIG. 1  of the above-mentioned document shows a parallel-flow condenser of this type and also proposes a process for producing condensers of this type. To produce the flat tubes, a sheet-metal strip is shaped into the flat tube and welded using a longitudinal seam. A second sheet-metal strip is formed with corrugations running in the transverse direction and is inserted into the flat tube. The peaks and valleys of the corrugations are soldered to the wide sides of the flat tube, so as to form inner passages running in the longitudinal direction which have hydraulic diameters within the above-mentioned range (cf.  FIG. 2  of the above-mentioned document). 
         [0004]    In many other cases, flat tubes for condensers and/or evaporators are produced by extrusion, in which case there are manufacturing engineering limits on the realization of particularly small hydraulic diameters combined with significantly smaller tube wall thicknesses and passage wall thicknesses. From a cost perspective too, the extrusion process does not always stand comparison with other processes. This is true at least if the flat tubes have dimensions (D;d) as required for condensers/evaporators. 
         [0005]    Furthermore, in the case of flat tubes for condensers and/or evaporators, it is necessary to take into account the significantly higher internal pressure compared to other heat exchangers in motor vehicles, which has meant that in practice hitherto the tube wall thickness of flat tubes of this type has been at best approximately between 0.25 mm and 0.30 mm. The hydraulic diameters of current commercially available flat tubes for condensers and/or evaporators are in the range from approximately 1.10-1.60 mm or slightly above. 
         [0006]    There are also a number of earlier patent applications in the name of the applicant, but these have not at present been published. One of these bears the application number DE 10 2006 006 670.7 and proposes flat tubes with extremely small wall thicknesses for cooling liquid coolers and for charge air coolers. 
         [0007]    Another convention heat exchanger is disclosed in EP 1 681 528 A1. This publication specifically claims flat tubes for condensers. It represents an advanced stage of development, since it likewise relates to very thin-walled flat tubes. The sheet-metal strip forming the passages is to have a thickness of less than 0.1 mm. In the Applicant&#39;s opinion, the flat tubes disclosed in that document, despite all their advantages, also have a significant drawback, namely that the stability of the flat tubes is insufficient. 
         [0008]    One independent object of the invention is to provide lightweight but also high-performance and low-cost condensers and/or evaporators or flat tubes for them which are to have improved stability. Some embodiments of the present invention achieve this and other desirable objects. 
         [0009]    According to the invention, both narrow sides of the flat tube are reinforced in that they are to have a thickness which is greater than the tube wall thickness, for example at least double the tube wall thickness. This proposal simplifies production of the heat exchanger network comprising flat tubes of this type and also corrugated fins, since this network becomes easier to assemble. In the case of flat tubes from the prior art, which have only a single reinforced narrow side, it is necessary to ensure that all the flat tubes are positioned with the reinforced narrow side facing in one direction, generally forward toward the cooling-air stream. This consideration is obviated because the present proposal reinforces both narrow sides. 
         [0010]    Furthermore, according to an embodiment which is currently preferred, the flat tube comprises three sheet-metal strips, two sheet-metal strips forming the tube wall and the third sheet-metal strip representing an inner insert. 
         [0011]    In a refinement of this idea, the two sheet-metal strips which form the tube wall are identical in form, in that one longitudinal edge of the sheet-metal strips has a larger arc and the other longitudinal edge of the sheet-metal strips is configured with a smaller arc, the sides of the sheet-metal strips being disposed oppositely to one another in such a manner that the larger arc of one longitudinal edge of one sheet-metal strip engages around the smaller arc of the longitudinal edge of the other sheet-metal strip, and vice versa. 
         [0012]    Further reinforcement of the two narrow sides is achieved by the inner insert having two deformed longitudinal edges which bear against the inside of the narrow sides. 
         [0013]    Alternatives provide for it to be possible to produce the flat tube either from one single sheet-metal strip or from two sheet-metal strips. 
         [0014]    In the case of flat tubes which can be produced from two sheet-metal strips, one narrow side comprises a bend which lies in a fold of the sheet-metal strip and the other narrow side is formed by one longitudinal edge of the sheet-metal strip being configured with a larger arc, which is placed around a smaller arc at the other longitudinal edge of the sheet-metal strip, the second sheet-metal strip being configured as a corrugated inner insert, the longitudinal edges of which bear or do not bear against the inside of the narrow sides. 
         [0015]    The passage wall thickness is approximately between 0.03-0.10 mm or slightly above. In the case of flat tubes made from a single sheet-metal strip, the tube wall thickness and the passage wall thickness have the same dimensions. 
         [0016]    The tube wall thickness is in the range from approximately 0.08 mm-0.20 mm, with the passage wall thickness being between 0.03-0.10 mm. This applies to both two-part and three-part flat tubes. 
         [0017]    In terms of the flat tube dimensions, the small dimension (d) of the flat tube is approximately 0.8-1.3 mm and the large dimension (D) is approximately between 8 and 20 mm, preferably approximately 12-16 mm. 
         [0018]    It has been concluded that a particularly suitable hydraulic diameter of the passages is between 0.30 and 0.70 mm, with a range between 0.40 and 0.60 mm standing out in particular by virtue of performance advantages. 
         [0019]    The condenser or evaporator as a component of an air-conditioning system of motor vehicles which condenser or evaporator has a soldered heat exchanger network made up of flat tubes and fins which are disposed between the flat tubes and through which cooling air flows is described in greater detail below. 
         [0020]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The accompanying drawings predominantly show a plurality of enlarged views of various flat tube cross sections, which can advantageously be used for condensers of air-conditioning systems. In the drawings: 
           [0022]      FIG. 1  shows a flat tube produced from three sheet-metal strips; 
           [0023]      FIG. 2  shows a flat tube according to an alternate embodiment which can be produced from three sheet-metal strips; 
           [0024]      FIGS. 3 ,  4 ,  5 , and  7   a - 7   d  show further modified flat tubes comprising three sheet-metal strips; 
           [0025]      FIGS. 6 ,  8 , and  9  show different flat tubes which comprise a single deformed sheet-metal strip; and 
           [0026]      FIG. 10  shows a flat tube which can be produced from two sheet-metal strips. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
         [0028]    All the flat tubes have the common features whereby the hydraulic diameter h D  of the passages K is greater than 0.254 mm, the tube wall thickness W d  is less than 0.25 mm and both narrow sides  1  are reinforced by having a greater wall thickness S d  than the remaining tube wall thickness W d . The passage wall thickness K d  may be between 0.03 and 0.15 mm. 
         [0029]    The flat tubes illustrated in  FIGS. 1-3 ,  5 , and  7  comprise three sheet-metal strips a, b, c and constitute the currently preferred embodiments, with the flat tubes from  FIG. 7  constituting the variant which is at present most preferred. The flat tubes in the above-mentioned figures all have the feature that the two sheet-metal strips a and b which form the wall parts are identical in form and are arranged oppositely in terms of their sides. One longitudinal edge of the sheet-metal strips a and b was formed with a larger arc and the other longitudinal edge was provided with a smaller arc. As a result of the opposite arrangement, the larger arc of one sheet-metal strip a engages around the smaller arc on the other sheet-metal strip  6  in order to form one narrow side  1  of the flat tube, and the larger arc on the other sheet-metal strip b engages around the smaller arc on the first sheet-metal strip a in order to form the other narrow side  1  of the flat tube. Furthermore, the flat tubes of the above-mentioned figures also have the common feature that the third sheet-metal strip c represents an inner insert, the two longitudinal edges of which bear against the inside of the narrow sides  1  and additionally reinforce the latter. This text refers to sheet-metal strips a, b, c, because the flat tubes are produced from endless sheet-metal strips on a rolling mill train and are then cut to the required length, which is not shown here. 
         [0030]      FIG. 1  differs from  FIG. 2  with regard to the form of the inner insert c.  FIG. 2  shows the possibility of the corrugation geometry or the configuration of the chambers K possibly being different, in order to take account of specific thermodynamic conditions or in order to achieve advantages in this respect. Furthermore, the left-hand narrow side  1  of the flat tube from  FIG. 2  indicates that the inner insert c may also be folded against the longitudinal edge in order to additionally reinforce the narrow sides  1 . Although this possibility has been shown for only one longitudinal edge, it will be clear that it is also possible for both longitudinal edges of the inner insert c to be formed in this way. 
         [0031]    The exemplary embodiment shown in  FIGS. 3 and 4  is particularly suitable for inner inserts c which are produced from extremely thin sheet-metal strips. This may mean sheet-metal thicknesses of 0.03 mm or slightly more. The sheet-metal thickness of the wall parts a and b is also very small, for example around 0.10 mm. To allow sufficient reinforcement of the narrow sides  1  at this point too, the longitudinal edges of the inner insert c have been folded horizontally a number of times and placed against the inside of the narrow sides  1 . The horizontal folds of the longitudinal edges of the inner insert c mean that here the thickness S d  of the narrow sides  1  is even a multiple of the thickness W d  of the remaining tube wall—up to 5-8 times or even more could quite easily be advantageous. 
         [0032]    The two flat tubes illustrated in  FIG. 5  differ in terms of the geometry of their chambers K and by the fact that the above-mentioned measure of folding the two longitudinal edges of the inner insert c has been implemented in the lower of the two illustrations but not the upper one. 
         [0033]    The four illustrations corresponding to  FIGS. 7   a - 7   d  differ firstly with regard to the choice of thickness of the sheet-metal strips a, b and c and also the hydraulic diameters h D  of the passages K. The hydraulic diameters in the upper illustration are smaller, being approximately 0.5 mm. Moreover, the edge configuration of the inner insert c has been modified slightly. The lowest values are to be found in the exemplary embodiment corresponding to  FIG. 7   d , where the hydraulic diameter h D  is, for example, approximately 0.455 mm, the tube wall thickness W d  is approximately 0.115 mm and the passage wall thickness K d  is approx. 0.05 mm. As is known, the hydraulic diameter h D  is given by h D =4×A/U, where A represents the cross-sectional area of the passage K and U represents the wetted periphery of the passage K. 
         [0034]      FIG. 6  shows suitable embodiments of a soldered flat tube comprising a single sheet-metal strip. Accordingly, the flat tube does not have a separate inner insert. Rather, chambers K have been produced by in each case a fold  10  formed in a wide side  2 , said fold being supported against the other wide side  2 . The narrow sides  1  have in each case been produced from numerous horizontally disposed folds F which, as shown in the figures, provide a thickness of the narrow side  1  which amounts to a multiple of the thickness of the sheet-metal strip. 
         [0035]      FIG. 8  shows another flat tube made from a single sheet-metal strip in an intermediate stage shortly before completion. This flat tube is to comprise one sheet-metal strip with a thickness W d  which is closer to the upper limit, i.e. could be for example 0.20 mm. The reason for this could be that the thickness S d  in the narrow sides  1  is only double the thickness of the sheet-metal strip or the tube wall thickness W d . 
         [0036]    By contrast,  FIG. 9  shows that it is possible to form very stable narrow sides  1  even in the case of flat tubes comprising just one sheet-metal strip. For this purpose, it is then possible to select a sheet-metal strip with a thickness approximately between 0.10-0.15 mm. To produce this flat tube, two spaced-apart folds F are formed in the sheet-metal strip. Then, a bend B is produced in each of the folds F, thereby forming the narrow sides  1  of the flat tube. However, it is previously also necessary to have corrugated a portion of the sheet-metal strip, thereby forming the passages K in the closed flat tube, as shown in the figure. 
         [0037]    Finally,  FIG. 10  shows a flat tube with passages K which has been produced from two sheet-metal strips a, c. The sheet-metal strip a forms the tube wall, whereas the sheet-metal strip c forms an inner insert. The sheet-metal strip a may in this case have a thickness of approximately 0.20 mm. The thickness of the inner insert c is only approximately 0.15 mm or less, for example 0.10 mm. First of all, a fold F is formed in the sheet-metal strip a. In this exemplary embodiment, a small arc is formed at one longitudinal edge of the sheet-metal strip a. The other longitudinal edge of the sheet-metal strip a may likewise already have been preformed, so that it can subsequently be placed around the small arc. The sheet-metal strip c, i.e. the inner insert of the flat tube, is provided with a corrugated formation and with two deformed longitudinal edges. Then, the inner insert c is introduced into the flat tube, which can be gradually closed up. As the flat tube is being closed up, a bend B is produced in the above-mentioned fold F, resulting in the formation of the narrow side  1  located at the top in the figure. In the closed flat tube, the two longitudinal edges of the inner insert c bear against the inside of the narrow sides  1  of the flat tube. A number of steps of the production process described have been illustrated in  FIG. 10 . 
         [0038]    Various features and advantages of the invention are set forth in the following claims.