Patent Publication Number: US-2007114007-A1

Title: Heat exchanger

Description:
The present application is a divisional of U.S. application Ser. No. 10/493,467, filed Jun. 22, 2004, which is the national stage of PCT/EP02/09487 filed Aug. 24, 2002, the entire contents of which are incorporated herein by reference.  
      The invention relates to a heat exchanger, in particular an exhaust gas heat exchanger, heat exchanger, having a fluid channel, such as a tube or multiplicity of tubes, like a tube array, through which a first medium, such as exhaust gas, can flow, and a second fluid channel, such as a housing, through which a second medium, such as a coolant, can flow, the ends of the tube array being connected to the tube plates, for example in a cohesive manner, and the tube plates being connected to the housing, for example in a cohesive manner.  
      Such a heat exchanger as an exhaust gas heat exchanger has been disclosed by DE-A 199 07 163 from the applicant. In this known design, the ends of a tube array are accommodated in appropriate openings in a tube plate and are welded to the tube plate. The tube array with the two tube plates is arranged in the housing, the tube plates being welded circumferentially to the shell of the housing. Thus, the tubes are firmly connected to the housing via the tube plate, which can lead to thermal stresses under certain conditions. Hot exhaust gas flows through the tubes on the inside and colder coolant flows on the outside and also washes around the inside of the housing. In particular in the case of relatively long tube lengths of such an exhaust gas heat exchanger, for example for commercial vehicles, the different expansions of tubes and housing shell can lead to stresses which are no longer permissible, which can result, for example, in destruction of the tube-plate connection.  
      It is therefore an object of the invention to improve an exhaust gas heat exchanger of the type mentioned at the beginning to the effect that thermal stresses on account of different expansions are reduced or avoided, so that the heat exchanger achieves the service life which is normal in motor vehicles.  
      This object is achieved by the features of patent claim  1 .  
      In a heat exchanger, such as in particular an exhaust gas heat exchanger, having a fluid channel, such as a tube array, through which a first medium, such as exhaust gas, can flow, and a second fluid channel, such as a housing, through which a second medium, such as a coolant, can flow, the ends of the tube array being connected to the tube plates, for example in a cohesive manner, and the tube plates being connected to the housing, for example in a cohesive manner, the object is preferably achieved by the housing having an expansion element.  
      It is expedient in this case if a sealing element, such as a metal bellows, is arranged on the housing, covering and sealing the expansion element.  
      It can also be advantageous if the expansion element is formed in one piece with a sealing element.  
      Furthermore, it is expedient if the expansion element is formed as a circumferential bead.  
      It is particularly advantageous, moreover, if a sealing element, such as a metal bellows or another sealing element, for example made of plastic or an elastomer, is arranged on the housing, covering and sealing the expansion element.  
      The expansion element can also be formed in one piece with the sealing element, for example as a circumferential bead, which performs the sealing function and the expansion function at the same time.  
      It is advantageous in this case if the expansion element is at least one region of the housing that is provided with slots. It is expedient in this case if, as an expansion element, the housing or a region of the housing has slots which run transversely with respect to the longitudinal direction of the tubes and in the circumferential direction of the housing, which in each case extend only over part of the circumference and which in the circumferential direction partly overlap slots arranged offset axially.  
      In this case, in one exemplary embodiment, it can be expedient if at least one group of slots having at least two slots is provided in the housing. It is advantageous if the at least one group of slots is arranged in a central region of the housing, as viewed in the longitudinal direction of the heat exchanger. It is also advantageous if the at least one group of slots is arranged in an end region or close to an end region of the housing, as viewed in the longitudinal direction of the heat exchanger.  
      In a further exemplary embodiment, it is advantageous if two groups of slots are provided. In this case, it can be advantageous if the two groups of slots are arranged in the two end regions or close to the end regions of the housing. Likewise, it can be expedient if the groups of slots has at least two or a multiplicity of slots, such as three, four, five, six, etc. slots.  
      According to a further idea of the invention, it can be expedient if four slots are arranged in the housing or in a group of slots, in each case two extending over less than half the circumference in one of two transverse planes and slotted regions of the other transverse plane being located opposite the non-slotted regions of a transverse plane.  
      According to the invention, in a further exemplary embodiment it is expedient if, given an arrangement of two slots per group of slots, the slots are spaced apart and are formed in such a way that they run beside one another in a subregion of their extent and leave a narrow land between themselves.  
      In a further embodiment of the invention, it is expedient if, given an arrangement of three slots per group of slots, the slots are spaced apart and are formed in such a way that they run beside one another in a subregion of their extent and leave two narrow lands between themselves.  
      It can also be expedient if, given a group of slots, at least two lands or a multiplicity of lands, such as three, four, etc., are formed, as viewed over the circumference of the housing.  
      It is likewise advantageous if, given a group of slots with an arrangement of two lands per group, the lands lie opposite one another, as viewed in the radial direction of the housing.  
      Moreover, it is expedient if, given a group of slots with an arrangement of two or more lands per group, the lands are distributed uniformly, as viewed in the circumferential direction of the housing.  
      It is advantageous if four lands are formed by four slots which partly intersect at four points of the housing, that is to say that in each case two slots partly intersect in a region and thus form the land.  
      It is expedient if four times two parallel lands are formed by six slots which partly intersect at four points of the housing.  
      It is also expedient if the slots have a teardrop shape in their end regions.  
      Moreover, it is expedient if the slots are introduced into the housing by means of one of the following processes: laser cutting, water jet cutting, sawing, milling, erosion or punching.  
      It is also advantageous if the expansion element and/or the sealing element is formed from one of the following materials: metal, steel, elastomer, silicone.  
      Likewise, it is expedient if the expansion element and/or the sealing element is connected to a housing part or two housing parts or is formed in one piece with the latter.  
      According to the invention, it is expedient if the expansion element and/or the sealing element is connected to the housing by welding, soldering, by means of clamping elements or by means of adhesive bonding.  
      If, in the case of such an exhaust gas heat exchanger, differential expansion occurs between the exhaust gas tubes and the housing shell, then, on account of the slots running transversely with respect to the longitudinal direction of the tubes, the housing is capable of expanding in the same way as the tubes. This takes place as a result of elastic deformation of the housing shell in the region of the slots, more precisely between two axially offset slots. In order that the coolant which washes around the tubes does not emerge into the open from the slots in the housing, a metal bellows is arranged on the housing over the region of the slots, ensuring the necessary sealing and at the same time being able to follow the expansions of the housing. On account of these measures, thermal stresses and component damage or destruction caused by them are avoided, even in the case of long heat exchanger lengths. 
    
    
      An exemplary embodiment of the invention is illustrated in the drawing and will be described in more detail in the following text. In the drawing:  
       FIG. 1  shows a perspective view of part of an exhaust gas heat exchanger,  
       FIG. 2  shows a plan view of part of an exhaust gas heat exchanger,  
       FIG. 3  shows a side view of the part of the exhaust gas heat exchanger according to  FIG. 2  and  
       FIG. 4  shows a view of part of the exhaust gas heat exchanger with metal bellows,  
       FIG. 5  shows an extract of a heat exchanger,  
       FIGS. 6   a  to  6   c  show a view of arrangements of slots and lands, and  
       FIG. 7  shows a partial view of a heat exchanger. 
    
    
       FIG. 1  shows a perspective view of part of a heat exchanger, such as in particular an exhaust gas heat exchanger  1 , having a housing shell  2  which is approximately rectangular in cross section and which, in its end region  3 , is somewhat enlarged in cross section. However, the cross section can also have another geometry, such as round, polygonal, octagonal etc. The end  4  reveals the tube plate  5  with rectangular openings to accommodate fluid channels, such as exhaust gas tubes, which are not illustrated. The ends of these exhaust gas tubes are—as described, for example, in DE-A 199 07 163 already mentioned—welded to the tube plate which, in turn, is welded circumferentially to the housing shell  3 . Provided in the housing region  3  is an opening  7  for the inlet of coolant, which is distributed in the interior of the housing region  3  in an annular channel, not illustrated, and from there flows through the heat exchanger on the outer side of the exhaust gas tubes. Finally, approximately in the transition region of the housing regions  2  and  3 , three slots  8 ,  9  and  10  running in the circumferential direction of the housing can be seen, the slot  10  being offset axially with respect to the two slots  8  and  9  and likewise being offset in the circumferential direction.  
       FIG. 2  shows these slots  9  and  10  in a plan view of the housing  2 / 3  of the heat exchanger  1 . The slots  9  and  10  extend in the direction of the circumference of the housing as far as a circular or teardrop-shaped opening  11  or  12 , respectively, which is intended to avoid notch stresses in this region. The slot  9  reaches as far as the outer edge  13 , and the slot  10  as far as the outer edge  14 .  
      As can be seen in  FIG. 3 , the slot  9  runs onward in the circumferential direction from the edge  13  as far as the circular hole  15 , and the slot  10  runs onward from the edge  14  as far as the circular hole  16 . Both slots  9  and  10  are offset axially approximately by a region of a few mm, for example 5 mm. The tube plate is indicated at the front end of the housing  3  by a dashed line  5 . The entire exhaust gas heat exchanger  1  is illustrated incompletely in  FIGS. 1, 2  and  3 , inasmuch as a seal for the slots  9  and  10  with respect to the outside is missing—this seal, in the form of a metal bellows, will be described in  FIG. 4 .  
       FIG. 4  shows a view of part of the heat exchanger with the two housing regions  2  and  3 , a metal bellows  20  being arranged between these two regions—said bellows covers the slots, which cannot be seen in this depiction, as have been described in the previous FIGS.  1  to  3 . The metal bellows is matched to the cross section of the housing  2 / 3  and tightly connected to the latter via its circumferential edges  21  and  22 . As a result, coolant can no longer emerge to the outside from the interior of the housing via the slots—at the same time this metal bellows  20  is able to compensate for the expansions of the two housing regions  2  and  3 .  
       FIG. 5  shows a part of a heat exchanger  100  in which four slots  110  to  113  are introduced into the wall  101  of the housing, the slots being offset axially and in the circumferential direction in such a way that lands, which act as expanding or bending beams, remain between the slots.  
      As a result, one part of the heat exchanger can expand in such a way that the housing shell of the heat exchanger is flexible as a result of the bending beam or beams and ensures expansion of the housing.  
      As shown in  FIG. 5 , two bending beams are formed by the lands  120  to  123  for each face of the housing, this being the case on all four faces, that is to say even on the faces which cannot be seen in this view.  
       FIGS. 6   a  to  6   c  show variants of designs of slots and lands which are machined into the housing shell in order to form the bending beams.  
      In  FIG. 6   a,  two slots  150 ,  151  are formed or introduced into the housing. Between the slots there is a land  153 , which serves as a bending beam. Provided at the ends of the slots are teardrop-shaped cutouts.  
      In  FIG. 6   b,  two slots  160 ,  161 ,  162  are formed or introduced into the housing. Provided between these slots are two lands  163  and  164 , which serve as bending beams. Teardrop-shaped cutouts are provided at the ends of the slots.  
      The configuration of the slots of  FIG. 6   c  corresponds substantially to the configuration of  FIG. 6   b,  the slots being angled over in a region  170 ,  171 . These regions can also be curved.  
       FIG. 7  shows a partial view of a heat exchanger  200  with fluid channels through which a first medium can flow. In the exemplary embodiment of an exhaust gas heat exchanger, these are the fluid channels through which the exhaust gas flows.  
      A second medium can flow between the fluid channels  201  and possibly around the latter as a further fluid channel, in order to cool the medium in the first fluid channel. This second fluid channel is therefore located within the housing  202 .  
      For the purpose of improved mechanical decoupling on account of the different thermal expansion of the walls of the channels  201  and the housing  202 , a circumferential bead  210  is introduced into the housing at at least one point. As a result, the housing, which is generally at a lower temperature than the inner channels during the operation of the heat exchanger, is able to expand when the inner channels expand on account of the thermal expansion, without destruction of the heat exchanger occurring.  
      The bead  210  is in this case constituted, for example, by a semicircular bulge. However, it can also have another form, such as in a folded or meandering configuration. The bead can also be bulged inward, that is to say formed as an indentation. During the formation of the bead, it is expedient for the latter to be able to fulfill both expansion characteristics and sealing characteristics.