Abstract:
The invention relates to a heat exchanger, especially a gas cooler for CO2, embodied as a cooling agent. The heat exchanger comprises at least one two-part collector unit made of a base and a cover. Said collector unit consists of flat pipes and at least two longitudinal channels with an essentially circular cross-section. The ends of the flat pipes and the base comprise openings for receiving the ends of the pipes. The base, cover and flat pipes are soldered together.

Description:
BACKGROUND OF THE INVENTION  
     The invention relates to a heat exchanger. 
     Heat exchangers for air-conditioning systems using R134a as refrigerant comprise a heat exchanger network made up of flat tubes and corrugation fins, as well as collection tubes which are arranged on both sides of the network and are preferably circular in cross section, as are known from DE-A 42 38 853 in the name of the present Applicant. Designs of this type have a sufficient strength to cope with the pressures which occur in a condenser. However, with more recent refrigerants, such as CO 2 , the pressures are considerably higher and the conventional designs of heat exchangers are no longer able to cope with such pressures. Therefore, in the extruded collection tube of increased wall thickness disclosed by WO 98/51983, it has been proposed that a collection tube comprise four flow passages of circular cross section arranged next to one another. An extruded collection tube of this type is expensive to produce, on account of the tooling required. Another type of collection tube for high internal pressures has been proposed in DE-A 199 06 289, in which the collection tube is assembled from two or three extruded or pressed parts and has two longitudinal passages which are circular in cross section. If this known collection tube is composed of extruded parts, the relatively high tooling costs are disadvantageous; if the known collection tube is composed of pressed parts, the shape appears to be incomplete, i.e. inadequately adapted to the expected stresses caused by the high internal pressure. 
     A further design of the header of a conventional condenser has been disclosed by U.S. Pat. No. 5,172,761. The condenser has flat tubes which are received in slot-like openings in a substantially planar but profiled tube plate. A substantially planar but also profiled cover part is connected to the tube plate. The tube plate and cover form individual chambers which are divided by transverse walls and in which the refrigerant flows or is diverted. Although the tube plate and cover are brazed to one another in the region of the tubes by means of inwardly facing stamped formations, this shape of a header does not appear suitable for relatively high pressures, as occur in particular in a CO 2  refrigerant circuit. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to improve a heat exchanger of the type described in the introduction in such a manner, in terms of the design of the header, that it can be produced easily and at low cost and is better able to withstand the high demands in terms of internal pressure. 
     The header is produced from two stamped or bent sheet-metal plates, i.e. there is no material-removing machining step. This leads to low production costs. Furthermore, the stamping of the metal sheet produces cold work-hardening, which increases the ability of the header to withstand internal pressure. The stamping operation forms longitudinal partitions with contact surfaces and transverse passages both at the cover and at the tube plate, with the contact surfaces each being arranged between the tubes or the openings in the tube plate. When joining the cover and tube plate, the contact surfaces bear flat against one another and thereby form a large number of brazing surfaces in the region of the longitudinal partition. Therefore, the tube plate and cover are brazed, on the one hand, in the edge region and, on the other hand, in the region of the partition, where the brazed contact surfaces form “tie rods”, increasing the resistance to the internal pressure which occurs within the header. This creates a pressure-resistant and inexpensive header. 
     The end sides of the longitudinal passages may, for example, be closed off by stoppers, covers or terminating walls and, if appropriate, then brazed, or may be provided with refrigerant connections. The end sides of the longitudinal passages can also be closed off by suitable deformation of the cover and/or tube plate by them being brazed together. The flat tube ends which project into the tube plate or header are bridged in the region of the longitudinal partition by the curved transverse passages, so that the refrigerant can flow into or out of the flat tubes over the entire cross-sectional region. 
     According to an advantageous refinement of the invention, the contact surfaces on the inner side of the header are formed as elevations and on the outer side of the header are formed as recesses or stamped indentations, with the recesses or stamped indentations and elevations or stamped projections corresponding to one another in terms of their position. This production and formation of the elevations on the inner side ensures a planar bearing surface and therefore secure and strong brazing. 
     According to a further advantageous configuration of the invention, the transverse passages, i.e. the connections from one longitudinal chamber to others, are designed as recesses on the inner side and accordingly as elevations on the outer side. The formation of the transverse passages on the inner side ensures free outlet cross sections of the flat tubes and good brazing of the flat tube ends to the inner side, on account of the formation of a meniscus. 
     In a further configuration of the invention, the wall thickness is approximately constant in the region of the longitudinal partitions of the tube plate and cover, and the elevations and recesses are preferably formed symmetrically with respect to a central parting plane, with a trapezoidal contour as seen in longitudinal section. This design results in a favorable fiber profile for the sheet-metal material and good cold work-hardening, i.e. a high toughness and strength of the header, in particular in combination with the brazed, rectangular contact surfaces between the flat tubes as tie rods. According to another embodiment, the header has a centrally arranged parting plane, and the elevations and recesses are arranged asymmetrically with respect to the parting plane. 
     According to an advantageous refinement of the invention, the tube plate (or also the cover) has edge strips or tabs in the edge region. The cover and tube plate are therefore fixed by means of the strips or tabs before they are brazed together with the entire heat exchanger. 
     According to a further advantageous configuration of the invention, there are three or more longitudinal chambers having two or more longitudinal partitions, with the longitudinal partitions being formed analogously to the individual longitudinal partition described above. This allows the header according to the invention to be used even for relatively large depths of flat tube without the longitudinal passages adopting an excessively large diameter. This gives advantages in terms of installation space and the strength of the header. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Exemplary embodiments of the invention are illustrated in the drawings and described in more detail in the text which follows, in which: 
         FIG. 1  shows a perspective partial view of a gas cooler, 
         FIG. 2  shows a side view of the gas cooler illustrated in  FIG. 1 , 
         FIG. 3  shows a partial view of the gas cooler shown in  FIG. 1  from the front, 
         FIG. 4  shows a section on line IV-IV in  FIG. 3 , 
         FIG. 5  shows an enlarged section as shown in  FIG. 4 , but without the flat tube, 
         FIG. 6  shows a section on line VI-VI in  FIG. 2 , 
         FIG. 7  shows a cross section through the tube plate of the header, 
         FIG. 7   a  shows a view from below onto the header shown in  FIG. 7 , 
         FIG. 7   b  shows a view from above onto the header shown in  FIG. 7 , 
         FIG. 8  shows a cross section through the cover of the header, 
         FIG. 8   a  shows a view from below onto the cover shown in  FIG. 8 , 
         FIG. 8   b  shows a view from above onto the header shown in  FIG. 8 , 
         FIG. 9  shows a further exemplary embodiment of the invention with a header having three longitudinal passages, and 
         FIG. 10  shows a cross section through the header as shown in  FIG. 9 , without the flat tube, 
         FIG. 11  shows a cross section through the header with the flat tube, and 
         FIG. 12  shows a cross section through the header with the flat tube. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a heat exchanger which is designed as a gas cooler  1  and has a header  2  and flat tubes  3  which open out into the header and between which corrugation fins (not shown) may be arranged. A gas cooler of this type is used in refrigerant circuits for motor vehicle air-conditioning systems operated with CO 2  as refrigerant, but can also be used in general as a pressure-resistant heat exchanger. 
       FIG. 2  shows a side view of the gas cooler  1  with the header  2  which is composed of a tube plate  4  and a cover  5 . The tube plate  4  and cover  5  are approximately W-shaped and formed and arranged symmetrically with respect to a parting plane  6 , with the tube plate  4  having edge strips  7  which engage laterally around and fix the cover  5 . Tube plate  4  and cover  5  form two longitudinal passages  8 ,  9 , which are both substantially circular in cross section. According to another embodiment, the two longitudinal passage have different cross sections. The flat tubes  3  are received by the tube plate  4  and the ends of the flat tubes project into the longitudinal passages  8 ,  9  approximately as far as the parting plane  6 . The tube plate  4  and cover  5  are cut from a sheet-metal plate (not shown in more detail) and are converted into the form illustrated by stamping or bending, i.e. are produced without the need for a material-removing machining process. After the individual parts, such as flat tubes  3 , tube plate  4  and cover  5  have been joined, the entire gas cooler  1 , which may also have another header (not shown), is brazed. 
       FIG. 3  shows a front view of an excerpt from the gas cooler  1 , i.e. as seen in the direction of view onto the narrow sides of the flat tubes  3  and the continuous strip  7  of the tube plate  4 . Instead of the continuous strip  7 , it is also possible to provide individual tabs (not shown), since these substantially only have a fixing function for the subsequent brazing operation. As has already been mentioned, corrugation fins (not shown), over which ambient air flows in a direction perpendicular to the plane of the drawing, may be arranged between the flat tubes  3 . 
       FIG. 4  shows a section on line IV-IV in  FIG. 3 , i.e. a cross section through the header  2  with tube plate  4  which receives a flat tube  3  (not shown in section). A transverse passage  10 , which forms a through-connection, is arranged between the two longitudinal passages  8 ,  9 . 
       FIG. 5  shows an enlarged illustration of the header  2  without the flat tube  3 , having a slot-like opening  11  in the tube plate  4  for receiving the flat tubes  3 . As has already been mentioned, the header  2  has a parting plane  6 , with respect to which tube plate  4  and cover  5 , with the exception of the edge strips  7  and the receiving openings  11 , are formed approximately symmetrically, in particular in the region of a longitudinal partition which separates the two longitudinal passages and is formed from a longitudinal partition region  12  of the tube plate  4  and from a longitudinal partition region  13  of the cover  5 , which form contact surfaces  14 ,  15  bearing against one another. The contact surfaces  14 ,  15  which bear against one another are in each case arranged between the flat tubes  3  and therefore lie behind the plane of the drawing, in which the transverse passage  10  and—symmetrically with respect thereto—a further transverse passage  16  are located. The two transverse passages  10 ,  16  complement one another to form a common passage cross section. According to one embodiment, the two contact surfaces are of different sizes or have different cross sections, in particular in terms of width and/or length. 
       FIG. 6  shows a section on line VI-VI in  FIG. 2 , i.e. in the region of the longitudinal partition or the two longitudinal partition regions  12 ,  13 . The latter, in the region of the parting plane  6 , butt against one another by way of their contact surfaces  14 ,  15 , which are each arranged between the flat tubes  3 . The contact surfaces  14 ,  15  in tube plate  4  and cover  5  are each designed as elevations or stamped projections, opposite each of which there is a recess  17  in the cover or a recess  18  in the tube plate. The transverse passages  10  in the cover  5  are formed by recesses on the inner side, opposite which are elevations  19  in the cover; in a corresponding way, opposite the transverse passages  16  in the tube plate  4  are elevations  20  on the outer side of the tube plate. The elevations and recesses in each case produce a trapezoidally meandering profile with an approximately constant wall thickness s for the longitudinal partition regions  12 ,  13  of tube plate and cover. Since the elevations and recesses—as has already been mentioned—are produced by stamping, the result here is a favorable fiber profile and high cold work-hardening, which is particularly advantageous for absorbing tensile forces in this region. 
       FIG. 7  shows a cross section through the tube plate  4 ,  FIG. 7   a  shows a view of the tube plate  4  from below and  FIG. 7   b  shows a view of the tube plate  4  from above. The contact surfaces  14 , which are approximately rectangular in form, can be seen between the slot-like openings  11  in the tube plate on the inner side of the tube plate  4  in  FIG. 7   b . The recesses  18  lie opposite these contact surfaces  14  on the outer side of the tube plate  4  in  FIG. 7   a . The elevations on the outer side of the tube plate are denoted by  20 . 
       FIG. 8  shows the cover  5  in cross section,  FIG. 8   a  shows a view of the cover  5  from below and  FIG. 8   b  shows a view of the cover  5  from above, i.e. its inner side. The stamped depressions  17  can be seen as rectangular surfaces in  FIG. 8   a , with the contact surfaces  15  located opposite them as elevations on the inner side of the cover  5  ( FIG. 8   b ). The transverse passages  10  extend between the elevations  15 . 
     The contact surfaces  14  ( FIG. 7   b ) and the contact surfaces  15  ( FIG. 8   b ) approximately correspond to one another in terms of size and position, and after the tube plate  4  and cover  5  have been joined bear against one another and are brazed together in this region. For this purpose, the sheet-metal plates used as starting material for tube plate  4  and cover  5  may be plated with brazing solder on both sides. The base material for the sheet-metal plates and also the flat tubes  3  and, if appropriate, the corrugation fins is an aluminum alloy or various aluminum alloys. 
       FIG. 9  shows a further exemplary embodiment of the invention, specifically a gas cooler  21 , with a header  22  and a series of flat tubes  23  which are received by the header  22  at the end side. 
       FIG. 10  shows the header  22  in cross section without flat tube  23 . The header  22  has three longitudinal passages  24 ,  25 ,  26  which are formed by a tube plate  27  and a cover  28 . A continuous slot  29  having the dimensions of the ends of the flat tubes  23  has been formed in the tube plate  27 , preferably by stamping. The longitudinal passages  24 ,  25 ,  26  are formed by two longitudinal partitions  30 ,  31  which are formed similarly to the longitudinal partition described above, comprising longitudinal partition regions of tube plate and cover. Transverse passages  32  and  33  are also provided by recesses. The illustration reveals that the header according to the invention can be designed with any desired number of longitudinal passages, with the contact surfaces according to the invention for forming tie rods in each case being provided between two adjacent longitudinal passages. 
       FIG. 11  shows a section through a collection tube of a gas cooler  100  having the header  102 , which is also referred to as a collection tube. The header is of two-part configuration and is composed of a tube plate  104  and a cover  105 . The cover  105  is fitted into the tube plate. This is carried out in such a way that the side arms of the tube plate engage around the cover, so that side faces of the cover bear against inner surfaces of the tube plate. Tabs  135 , which can be deformed prior to the brazing process in order to secure the cover in the tube plate, are advantageously arranged on the tube plate. Partitions  134  can be introduced, for example pushed, into openings in the cover in order to divide the collection tubes. These partitions can likewise be secured by means of tabs. The partitions are advantageously approximately B-shaped in form and bear against the contour of the tube plate. Tube plate  104  and cover  105  form at least two, optionally also 3, 4 or more, longitudinal passages, which are both substantially circular or oval in cross section. The flat tubes  103  are received by the tube plate  104 , and their flat tube ends project into the longitudinal passages, approximately as far as a parting plane. Tube plate  104  and cover  105  are cut out of a sheet-metal plate (not shown) and converted into the shape illustrated by stamping or bending, i.e. produced without the need for a material-removing machining process. However, the production process may also be carried out in a different order, i.e. first of all the sheet-metal plate is deformed, and then the tube plate or cover is punched out. After the individual parts, such as flat tubes  103 , tube plate  104  and cover  105 , have been joined, the entire gas cooler  1 , which may also include another header (not shown), can be brazed. 
       FIG. 12  shows a further exemplary embodiment of the invention, in which the configuration of tube plate and cover are similar to in  FIG. 11 , except that in  FIG. 12  the tube plate and cover have been swapped over, i.e. in  FIG. 12  the side arms of the cover engage around the outside of the tube plate, and the tabs are formed on the arms of the cover. Another advantage in this case is that the tabs can come to bear laterally against the tubes  103  and/or may be arranged between two tubes. 
     In both cases, i.e.  FIG. 11  and  FIG. 12 , the tube plate and cover have two approximately semicircular regions which are connected by an approximately straight portion. Arms which are oriented approximately perpendicular with respect to the central region are provided on the parts, such as tube plate or cover, which engage around the respective other part. 
     It is also possible for further components, such as flanges or the like, to be connected to the tabs  135 . 
     LIST OF DESIGNATIONS 
     
         
           1 ,  100  Gas cooler 
           2 ,  102  Header 
           3 ,  103  Flat tube 
           4 ,  104  Tube plate 
           5 ,  105  Cover 
           6  Parting plane 
           7  Edge strip 
           8  Longitudinal passage 
           9  Longitudinal passage 
           10  Transverse passage 
           11  Opening in the tube plate 
           12  Longitudinal partition region, tube plate 
           13  Longitudinal partition region, cover 
           14  Contact surface, tube plate 
           15  Contact surface, cover 
           16  Transverse passage 
           17  Recess, cover 
           18  Recess, tube plate 
           19  Elevation, cover 
           20  Elevation, tube plate 
           21  Gas cooler 
           22  Header 
           23  Flat tube 
           24  Longitudinal passage 
           25  Longitudinal passage 
           26  Longitudinal passage 
           27  Tube plate 
           28  Cover 
           29  Slot 
           30  Longitudinal partition 
           134  Longitudinal partition 
           135  Tab