Abstract:
A heat exchanger including a plurality of longitudinal flat tubes stacked together with space between the broad sides of adjacent tubes, and inlet and outlet collecting tanks. The inlet collecting tank distributes a first medium into the tubes, and has a wall extending around the periphery of one end the stack of flat tubes over a selected longitudinal section, the wall having at least one of an inlet and outlet for a second medium distributed in the space between the stacked tubes. The outlet collecting tank receives the first medium from the tubes. Longitudinal internal inserts in the flat tubes are metallically connected to the broad sides of the associated flat tube. At least one row of cutouts is between the longitudinal ends of the internal inserts and in the selected longitudinal section, with the row of cutouts extending substantially across the broad width of the insert.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S)  
       [0001]     Not applicable. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable. 
     
    
     REFERENCE TO A MICROFICHE APPENDIX  
       [0003]     Not applicable.  
       TECHNICAL FIELD  
       [0004]     The present invention is directed toward heat exchangers, and particularly toward flat tube heat exchangers subject to alternating temperature loads.  
       BACKGROUND OF THE INVENTION AND TECHNICAL PROBLEMS POSED BY THE PRIOR ART  
       [0005]     Heat exchangers are, of course, old in the art in a variety of configurations. One such heat exchanger type includes an inlet collecting tank which distributes a medium to flat heat exchanger tubes and an outlet collecting tank which accepts the medium from the flat heat exchanger tubes. An internal insert is arranged in the flat heat exchanger tubes, with the insert being metallically connected to the two broad sides of the heat exchanger tube.  
         [0006]     In one particular form, the collecting tank has a wall that extends around the periphery of the end of a stack of heat exchanger tubes and over a certain length section of the heat exchanger tubes, in which the wall has at least one inlet and/or one outlet for the other medium which flows between the heat exchanger tubes. This particular form of heat exchanger and heat exchanger tube described above are described in the not previously published European Patent Application with Application No. EP 040 27 604.0, in which a slit on the end of the internal insert or a conical cutout open toward the end is provided. In accordance with that description, both expedients led to a noticeable improvement with respect to compensation of alternating temperature loads.  
         [0007]     However, even with the improvement of that described structure, it is still desirable to provide heat exchangers and heat exchanger tubes which can even betterwithstand the enormous alternating temperature loads encountered, for example, in an exhaust heat exchanger in an exhaust gas recirculation system.  
         [0008]     The present invention is directed toward overcoming one or more of the problems set forth above.  
       SUMMARY OF THE INVENTION  
       [0009]     In one aspect of the present invention, a heat exchanger is provided, including a plurality of longitudinal flat tubes stacked together with space between the broad sides of adjacent tubes, and inlet and outlet collecting tanks. The inlet collecting tank distributes a first medium into the tubes, and has a wall extending around the periphery of one end the stack of flat tubes over a selected longitudinal section, the wall having at least one of an inlet and outlet for a second medium distributed in the space between the stacked tubes. The outlet collecting tank receives the first medium from the tubes. Longitudinal internal inserts in the flat tubes are metallically connected to the broad sides of the associated flat tube. There is at least one row of cutouts between the longitudinal ends of the internal inserts and in the selected longitudinal section, with the row of cutouts extending substantially across the broad width of the insert.  
         [0010]     In one form of this aspect of the present invention, the internal insert is a.sheet corrugated in the longitudinal and transverse directions and the at least one row of cutouts includes at least two rows of cutouts with a connecting insert portion between the rows of cutouts. In a further form, the corrugated sheet includes wave flanks, and the connection insert portion is in the wave flanks. In another further form, the rows of cutouts extend no more than one third (⅓) of the total length of the internal insert and the remaining length of the internal insert has substantially no cutouts. In still another further form, the size and shape of the cutouts and the connecting insert portion is variable. In yet another further form, a row of end cutouts is open on the end of the internal insert in the selected longitudinal section, and an end connecting insert portion is between the row of end cutouts and an adjacent row of cutouts, and in a still further form the internal insert includes fingers in the crests and valleys of the corrugated sheet adjacent opposite sides of the end cutouts, with the fingers soldered on the inside wall of the associated flat tube.  
         [0011]     In another form of this aspect of the present invention, the at least one row of cutouts includes at least two rows of cutouts with a connecting insert portion between the rows of cutouts, and further includes at least one rupture site in the connecting insert portion.  
         [0012]     In still another form of this aspect of the present invention, the tubes are two flat tube halves connected on their longitudinal edges.  
         [0013]     In yet another form of this aspect of the present invention, outwardly projecting embossings are on the broad sides of the tubes, with the embossings defining the space between the broad sides of adjacent tubes in the stack of tubes.  
         [0014]     In another form of this aspect of the present invention, the collecting tank wall has deformations adapted to stabilize the tank while providing elasticity during alternating temperature loads.  
         [0015]     In still another form of this aspect of the present invention, the selected longitudinal section is bounded by first and second connection planes at one end of the stack of tubes, and the one inlet or outlet for the second medium is in the collecting tank wall between the two planes. In a further form, a tube plate is connected to the collecting tank wall at the first connection plane, with the tube plate having connectors for the ends of the stack of flat tubes. In another further form, an intermediate plate having the peripheral contour of the stack of flat tubes is connected to wall in the first connection plane. In still another further form, the second connection plane is defined by a contour cut in the collecting tank wall and matching the peripheral contour of the stack of flat tubes. In yet another further form, the contour cut in the collecting tank wall has slits matching an end flange on the flat tubes and also has protrusions closing furrows at the space between adjacent flat tubes. In another further form, the broad sides of the heat exchanger tubes include protrusions in the region of the first connection plane to divide the flow of the second medium in the space between adjacent tubes.  
         [0016]     In another form of this aspect of the present invention, the inlet collecting tank includes a diffuser for the first medium, and one of an. inlet and outlet for the second medium is in the selected longitudinal section.  
         [0017]     In still another form of this aspect of the present invention, the heat exchanger is an exhaust heat exchanger cooled with liquid in the exhaust gas recirculation system of vehicles.  
         [0018]     In yet another form of this aspect of the present invention, the heat exchanger is a charge air cooler.  
         [0019]     In another aspect of the present invention, a tube is provided for use with a heat exchanger with the tube including an end section connectable to a wall of at least one collecting tank, including a longitudinal flat tube with broad sides, and a longitudinal internal insert metallically connected to the tube broad sides and including at least one row of cutouts between the longitudinal ends of the internal insert in the end and extending substantially across the broad width of the insert.  
         [0020]     In one form of this aspect of the present invention, the internal insert is corrugated and the at least one row of cutouts includes at least two rows of cutouts with a connecting insert portion between the rows of cutouts. In a further form, the corrugated internal insert has wave flanks extending between opposite broad sides of the tube, and the connecting insert portion is primarily in the wave flanks. In another further form, the rows of cutouts extend over no more than one third (⅓) of the total length of the internal insert. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a face view of one embodiment of a heat exchanger incorporating the present invention;  
         [0022]      FIG. 2  is a perspective view of a collecting tank of the  FIG. 1  embodiment.  
         [0023]      FIG. 3  is a perspective view on one end of one embodiment of a heat exchanger tube incorporating the present invention;  
         [0024]      FIG. 4  is a perspective view on one end of a second embodiment of a heat exchanger tube incorporating the present invention;  
         [0025]      FIG. 5  is a perspective view of an intermediate plate usable with the present invention;  
         [0026]      FIG. 6  is a partially exploded perspective view of one end of a heat exchanger including the  FIG. 5  intermediate plate;  
         [0027]      FIG. 7  is a perspective view of the  FIG. 6  heat exchanger, with portions broken away to show the internal inserts of the heat exchanger tubes;  
         [0028]     FIGS.  8  to  14  are perspective views illustrating the ends of different embodiments of tube internal inserts incorporating the present invention;  
         [0029]      FIG. 15  is a cutout of a part of the core of the charge air cooler of  FIG. 16 ; and  
         [0030]      FIG. 16  is a partially exploded view of an air-cooled charge air cooler incorporating the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     The practical examples illustrated in  FIGS. 1-7  involve exhaust heat exchangers, such as may be advantageously incorporated in the exhaust gas recirculation system of a vehicle in a manner not shown, and which use the coolant of the vehicle engine as the cooling medium. The heat exchanger can be used with the same advantages, for example, as a charge air cooler cooled with coolant or for other purposes, especially where high alternating temperature loads occur.  
         [0032]     It should also be appreciated that the present invention may also be advantageously used, for example, with heat exchangers which are U-shaped, in which the inlet  20  and the outlet  21  are situated on the same collecting tank  24 a.  
         [0033]     In the Figures showing the practical examples, however, heat exchangers having collecting tanks on both ends of the stack of heat exchanger tubes  26  are depicted. As a result, in the heat exchanger depicted in  FIG. 1 , the exhaust flows into the left collecting tank  24   b,  is distributed to and flows through the paths  28  in the heat exchanger tubes  26 , and then leaves the heat exchanger via the other (right) collecting tank  24   b.  The coolant, on the other hand, enters the inlet  20  on the right collecting tank  24   a,  is distributed to the flow channels  30  which are arranged between the heat exchanger tubes  26  ( FIG. 6  or  7 ) and leaves the heat exchanger via the outlet  21  provided in the left collecting tank  24   a.    
         [0034]     The inlet  20  and the outlet  21 , in this practical example, have a roughly rectangular cross-section. Advantageously, a mount  36 , produced by deformation from sheet metal, was provided in each case on the collecting tank  24 a, which extends around three sides of the collecting tank  24   a  and is firmly soldered to it. The mount  36  has the inlet  20  or the outlet  21  and an appropriate sealing groove  38 , so that the heat exchanger can be flanged directly to a connection plane of a unit (not shown) and therefore fastened to it and simultaneously “supplied” with coolant.  
         [0035]     The stack of heat exchanger tubes  26  may advantageously be covered by an upper and lower reinforcement plate  76  ( FIG. 7 ) because the sheet thickness of the heat exchanger tubes  26  is relatively small. Both protection against the mechanical effect on tubes  26  and higher stability of the entire heat exchanger can be achieved by this.  
         [0036]      FIG. 2  shows the collecting tank  24   a  in a first variant in a perspective view, as present twofold in the practical example from  FIG. 1 , apart from the cross-sectional shape of the inlet  20  and outlet  21  (which are roughly rectangular in  FIG. 1  and round in  FIG. 2 ).  
         [0037]      FIG. 3  shows one of the seven heat exchanger tubes  26  present there. The wall  40  of collecting tank  24   a  has deformations  44 , which, by the way, can also be provided in the wall  40  of collecting tank  24   b  ( FIG. 1 ). In addition, there are two connection planes  50  and  54  between the wall  40  and the stack of heat exchanger tubes  26 . In one connection plane  54 , direct connection of the wall  40  to the tube stack is provided at an opening  60 , which represents the peripheral contour of the stack, which includes slits  64  and protrusions  66 . Each slit  64  accommodates a tube edge flange  70  (see  FIG. 3 ), and upper and lower gradations  74  accommodate the reinforcement plates  76 .  
         [0038]     In the other connection plane  50 , on the other hand, an indirect connection to the wall  40  is present, since, in this practical example, an intermediate tube plate  78  is provided. For this purpose, the edge of wall  40  has a gradation at  80  (see  FIGS. 2 and 6 ), so that the tube plate  78  has a seat with a stop in the wall  40 . The already mentioned slits  64  are also situated in the contour of tube plate  78  and serve the same purpose there.  
         [0039]     The edge of the opening  60  in the wall  40  and the edge of perforations of the tube plate  78  are formed with only a slight passage  82  (see  FIG. 2 ) pointing toward the center of the heat exchanger, which contributes to achievement of a perfect soldered connection with the tubes  26  even with a relatively limited thickness of the wall  40 , a perfect soldered connection with tubes  26  can be achieved. The passage  82  may be formed via corresponding design of the punching tool for production of the opening  60  and is therefore feasible without additional expense. Openings  60  according to this design are advantageously present in all practical examples of the exhaust heat exchanger, even if the other figures do not show it in detail.  
         [0040]     As also shown in  FIG. 3 , a longitudinal section or region  86  of the heat exchanger tubes  26  lies between the two connection plates  50  and  54 . The heat exchanger tubes  26  are combined in the stack direction  88  ( FIG. 6 ) into a stack of heat exchanger tubes  26 . The reinforcement plates  76  ( FIG. 7 ) are added on opposite sides of the stack. As further described below, internal inserts  90  are inserted in each case into heat exchanger tubes  26 , which consist of two identical flat tubes halves  26   a,    26   b  joined by bent brackets  92  on the edge flange  70 . Such tube structure is particularly cost-effective and is characterized by high process reliability, especially during soldering. The stack is combined via the longitudinal section  86  of the heat exchanger tubes to the collecting tank  24   a,  in which each edge flange  70  of each heat exchanger tube  26  comes to lie in the connection plane  54  in a slit  64  present there and, in the other connection plane  50 , sits in a slit  64  of tube plate  78  present there (see above).  
         [0041]     It should be appreciated that flat heat exchanger tubes as described herein are tubes which have a smaller and a larger inside dimension, and therefore include not only those with parallel broad sides but also include, for example, heat exchanger tubes with an oval cross-section. Moreover, it should be appreciated that flat heat exchanger tubes according to the present invention also include those formed by two plates forming the two broad sides in which the two narrow sides of the tubes are represented by a rod or the like inserted between the plates. Such designs are found in many applications of heat exchangers, and are also encountered, for example, in fuel cell systems.  
         [0042]      FIGS. 6 and 7  show one end  94  of the heat exchanger, where it is apparent that a flow channel  30  is formed in each case between the heat exchanger tubes  26  through which the coolant can flow. Specifically, as shown in  FIGS. 3-4 , the identical flat tube halves  26   a,    26   b  have longitudinal projections or embossings  100  along their edges which close off a flow channel  30  between two assembled heat exchanger tubes  26 . The embossings  100  seal off the flow channels so that an essentially housingless design may be achieved, which design is characterized by economic use of material with the highest efficiency of heat transfer. On the broad sides  102  of heat exchanger tubes  26 , additional spaced projections  104  are also present and, in the vicinity of the connection planes  50 , a row with protrusions  106  may be advantageously provided to make flow of the coolant which enters or emerges in that vicinity (see the arrows in  FIG. 4 ) uniform.  
         [0043]     As is further clearly shown in  FIG. 7 , corrugated internal inserts  90  are situated in the heat exchanger tubes  26 . The internal inserts  90  may have wave flanks  110  corrugated in the longitudinal direction and transverse direction (see the longitudinal section on the right of  FIG. 7 .  
         [0044]     In addition, the wave flanks  110  have cutouts  120  and intermediate connectors  130 . In the  FIG. 7  embodiment, seven rows  134  of round cutouts  120  are apparent, which are separated from each other by an intermediate connector  130 . It should be appreciated that length changes in the stack direction  88  of heat exchanger tubes  26 , occurring because of temperature changes, are permitted or compensated by this. In particular, the distinctness of the improvement in resistance to alternating temperature loads is surprising.  
         [0045]     Since the loads in exhaust heat exchangers reach the limit of what can be accomplished with ordinary materials (stainless steel, aluminum) and joining techniques (particularly considering cost-effective manufacturing methods of mass production) due to the level of the temperature differences and the frequency of the temperature alternations, the inventors hereof concerned themselves with demonstrating the advantages of the present invention with additional variations thereof.  
         [0046]     In that regard, in one variation the protrusions  106  and the flat tubes halves  26   a,    26   b  were modified so that, in the region of the connection plane  50 , groups of protrusions  106  were concentrated (see  FIG. 4 ) to divert the incoming coolant so that a significant part of it is initially directed to the connection plane  54  before it can flow further into flow channels  30 . Better temperature equalization is achieved by this and therefore the objective of improving the capability, relative to. alternating temperature loads, is also served.  
         [0047]     In an alternative embodiment, the tube plate  78  (see  FIG. 2 ) is replaced by an intermediate plate  140  (see  FIGS. 5 and 6 ), with the flat tube halves  26   a,    26   b  modified for this purpose (see  FIG. 4 ). Specifically, additional projections  144  extend across the broad sides  102  of the ends  94  of the flat tube halves  26   a,    26   b,  which projections  144  whose a height coinciding with the height of the embossings  100  running along the longitudinal sides. The additional projections  144  of adjacent heat exchanger tubes  26  lie against each other and each closes off a flow channel  30 . A traditional tube plate  78  with connectors  150  can therefore be dispensed with. As shown in the mentioned figures, the intermediate plate  140 , in similar fashion to the wall  40  in the other connection plate, is equipped with slits  64  and protrusions  66 , in order to correspond to the peripheral contour of the stock of heat exchanger tubes  26 . The protrusions  66  extend into furrows  154  (see  FIG. 6 ). Connection of the intermediate plate  140  to the wall  40  occurs via a gradation  80  of wall  40 , which provides a stop and seat for the intermediate plate  140 , as in the tube plate  78  that was described in conjunction with  FIG. 2 . The peripheral contour in the intermediate plate  140  also has shoulders  74  to accommodate the reinforcement plates  76  ( FIG. 7 ). By providing an intermediate plate  140 , an additional weight and cost reduction is achieved.  
         [0048]      FIG. 8  shows the end of a flat heat exchanger tube  26  with a further modified internal insert  90 , with the wave flanks  110  running between the broad sides  102  of the heat exchanger tube  26  having a bent contour making them also flexible in the direction between the broad sides  102 . Such heat exchanger tubes  26 , shaped and welded from a sheet strip, can be provided in the entire heat exchanger. It is particularly apparent from this depiction that the rows  134  of cutouts  120  and intermediate connectors  130  extend over the entire width of internal insert  90  and heat exchanger tube  26 , which is the preferred design.  
         [0049]     However, according to the present proposal, rows  134  are also spoken of, if the cutouts  120  and intermediate connectors  130  are not situated in all wave flanks  110 . The same applies for the design of the rows  134  themselves. Moreover, while only straight rows  134  are shown, zig-zag rows  134 , for example, are equally expedient and may be used within the scope of the present invention.  
         [0050]      FIGS. 9-14  illustration another embodiment incorporating the present invention in which a line-like wall thinning  158  was made in the flanks  110  of the corrugated internal inserts  90 , which serve as a rupture site  159  (see  FIG. 11 ) which passes through all intermediate connectors  130 . It is drawn as a line in  FIGS. 9-14 , which otherwise show different internal inserts  90  in partial views and make it clear that the shape and size of the cutouts  120  and intermediate connectors  130  are subject to no special provisions and can be designed according to the application, in order to achieve the desired advantages with respect to resistance to alternating temperature loads.  
         [0051]     As shown in  FIG. 10 , the cross-sectional shape of the cutouts  120  and the size of the individual cross-sections from the end of the internal insert  90  in the direction toward the center can be varied. Particularly widely protruding collars  160  are also shown in  FIG. 10 , which collars  160  have proven to be particularly advantageous during the soldering process which, as is known, occurs in a finely adjusted temperature range, in which the materials are already in a “doughy” state. The collars  160  prevent “falling” in the region of the connections caused by gravity in this state.  
         [0052]      FIGS. 15 and 16  show the use of flat heat exchanger tubes  26  in conjunction with an air-cooled charge air cooler. The charge air cooler has a collecting tank  24  with a wall  40 , with the ends  94  of the heat exchanger tubes  26  extending into openings of a tube plate  78  and, for example, soldered there. The tube plate  78  represents the connection plane  50 . The type of indirect connection provided in this example between wall  40  and heat exchanger tube  26  (via an intermediate tube plate  78 ) is unimportant. The sometimes extremely hot charge air flows through the heat exchanger tubes  26 , and cooling air flows through corrugated ribs  166  situated between tubes  26 . The connectors  150  between the openings in the tube plate  78  are provided with a cross-section contour (see, for example,  FIG. 6 ) in order to support the flexible behavior of the alternating temperature loads, and internal inserts  90  are situated in the tubes  26  (as illustrated by the cutout of two tubes  26   FIG. 16 ). The internal insert  90  has rows  134  of cutouts  120  and intermediate connectors  130  which extend, at least a bit, in the longitudinal direction of the internal insert  90 . Two or three such rows  134  may be sufficient to achieve the intended effects. The heat exchanger tubes  26  of this practical example are designed as welded flat tubes and have no elevations on their broad sides  102 , as an additional difference relative to the application as an exhaust heat exchanger. In this application, the much larger section of the internal insert  90 , not provided with cutouts  120  and intermediate connectors  130 , can be provided with indentations or similar formations that increase turbulence (not shown). The internal inserts  90 , however, as is preferably the case in the application as an exhaust heat exchanger, can also have fully closed wave flanks  110  in the mentioned much larger section.  
         [0053]     The use of the described features means that ruptures in the connection heat exchangertube/tube plate occur much more rarely. The individual parts of the heat exchanger consisting of metal are prepared, according to known methods, as required, so that they can be metallically connected in a soldering furnace.  
         [0054]     Because the internal insert as described has at least one row of cutouts with an intermediate connector (at least in the connection region of the flat heat exchanger tubes with the wall of the collecting tank) in order to compensate for alternating temperature loads, the resistance of the heat exchanger according to the invention to alternating temperature loads was significantly increased in comparison with the previously mentioned prior art, as demonstrated by evaluation of an extensive series of experiments. The number of achieved temperature alternations was increased to more than double, without the previous ruptures or leaks occurring. Improvements to this extent were not expected and make it clear that even apparently slight differences relative to the prior art can lead to significant advantages.  
         [0055]     Still other aspects, objects, and advantages of the present invention can be obtained from a study of the specification, the drawings, and the appended claims. It should be understood, however, that the present invention could be used in alternate forms where less than all of the objects and advantages of the present invention and preferred embodiment as described above would be obtained.