Abstract:
A housingless heat exchanger including a stack of flat tubes with at least two being cooling tubes and at least one being a bypass tube. Collecting tanks are on the tube ends and diffuse gas streaming in the tube flow paths. The flat tubes each comprise a connected pair of plates defining a flow path, and an enclosed space is defined between adjacent flat tubes. Coolant inlet and outlet channels are formed by connected plate openings connect to the enclosed space between the cooling tubes whereby coolant flows through that enclosed space. A switching valve in one collecting tank is movable between a cooling position in which the gas streams through the cooling tubes and a bypass position in which the gas streams through the bypass tube. A closure in the coolant inlet and outlet channels blocks coolant from adjacent the bypass tube. An insulating plate may also, or alternatively, be between the bypass tube and the cooling tube adjacent the bypass tube to block heat exchange between coolant and the bypass tube.

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 exhaust heat exchangers usable in vehicles.  
       BACKGROUND OF THE INVENTION AND TECHNICAL PROBLEMS POSED BY THE PRIOR ART  
       [0005]     Exhaust heat exchangers may be advantageously used, for example, to cool exhaust gas, allowing it to be recirculated for emission reduction in vehicles. The recirculated exhaust must be cooled in order to achieve high efficiency during recirculation, especially to achieve better degrees of filling. The entire system (i.e., the vehicle with its internal combustion engine) and an overall significantly reduced energy balance is naturally at issue.  
         [0006]     For many years, however, all the operating situations in the vehicle have been analyzed and measures taken according to many different operating situations to be encountered. One such measure consists of bypassing the exhaust heat exchanger in operating situations in which cooling of the exhaust would be counterproductive. Such operating situations include the starting phases of the vehicle, which require considerable fuel and in which the heat energy of the exhaust, for example, may be used directly for rapid warm-up of the engine to its optimum operating temperature. Solutions like those described in European patent applications/patents EP 916 837 and EP 987 427, and ordinarily propose bypassing the exhaust heat exchanger. Specifically, a valve is arranged in front of the exhaust inlet to the exhaust heat exchanger, whereby the valve may feed the exhaust stream, as necessary, through the exhaust heat exchanger or past it directly into the recirculation line. The bypass is integrated in the valve.  
         [0007]     Additional solutions have been described in German applications DE 197 33 964 A1 or DE 199 06 401 A1, which show the manner in which recirculation can occur. In the first named document, a bypass line and the exhaust heat exchanger are separated from each other, but both are apparently arranged in a common housing and the bypass line in the latter goes around the heat exchanger outside of it without both being enclosed by a housing. The exhaust heat exchangers themselves are apparently so-called tube bundle heat exchangers or coil tube heat exchangers. These exhaust heat exchangers do not appear to be particularly compact, which is of particular importance in the limited engine compartment space of motor vehicles.  
         [0008]     Bypassing the heat exchangers is generally also required in exhaust heat exchangers per se. That is, even in heat exchangers proposed decades ago and (still) used in heaters for the passenger compartments of vehicles, among other things, bypassing is desired because the heat demand is not permanently present. However, those exhaust heat exchangers also usually belong to the tube bundle type or coil tube type. Exhaust heat exchangers, as explained in EP 942 156 A1, are included here.  
         [0009]     Integrated bypasses have also been used heretofore, but in connection with heat exchanger designs which often must be manufactured by demanding welding methods, were described in DE 101 42 539 A1, in DE 199 62 863 A1 and in DE 195 40 683 A1.  
         [0010]     The present invention is directed toward overcoming one or more of the problems set forth above.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention relates to a heat exchanger having a housingless plate design in which flat tubes are formed by two deformed plates, the tubes being stacked with an inlet collecting tank being arranged at one end of the stack of flat tubes in the fashion of a diffusor, and an outlet collecting tank at the other end, for example, for exhaust or charge air which selectively flows through the flat tubes. Coolant for the air can be introduced into the tube stack and withdrawn from it through channels, the channels being formed by connected openings in the deformed plates.  
         [0012]     In one aspect of the present invention, a housingless heat exchanger is provided, including a stack of flat tubes with at least two of the tubes being cooling tubes and at least one of the flat tubes being a bypass tube, and at least one collecting tank on one end of the stack of flat tubes for gas streaming in the tube flow paths. Each of the flat tubes comprise a pair of plates connected to define a flow path therethrough, and an enclosed space is defined between adjacent flat tubes. Coolant inlet and outlet channels are formed by connected openings in the plates, with the channels being hydraulically connected to the enclosed space between the cooling tubes whereby coolant flows through the enclosed space between the cooling tubes. A switching valve in the collecting tank is movable between a cooling position in which at least most of the gas streams through the cooling tubes and a bypass position in which at least most of the gas streams through the bypass tube. A closure in the coolant inlet and outlet channels blocks coolant from adjacent the bypass tube.  
         [0013]     In one form of this aspect of the invention, the enclosed space between the bypass tube and the cooling tube adjacent the bypass tube includes at least a portion adjacent the bypass tube, and the closure blocks coolant from the enclosed space portion.  
         [0014]     In another form of this aspect of the invention, the cooling and bypass tubes have substantially the same configuration. In a further form, the pairs of plates of the cooling and bypass tubes are substantially the same as each other.  
         [0015]     In still another form of this aspect of the invention, the at least one bypass tube has a larger cross-section than at least one of the cooling tubes.  
         [0016]     In yet another form, the plates of the pairs of plates are joined about their edges, and the plates include contoured sections defining the enclosed spaces.  
         [0017]     In a still further form of this aspect of the invention, a insert is between the plates in the cooling tubes.  
         [0018]     In another aspect of the invention, the closure includes an insulating plate between the bypass tube and the cooling tube adjacent the bypass tube.  
         [0019]     In one form of this aspect, the insulating plate separates the enclosed space between the bypass tube and the cooling tube adjacent the bypass tube, whereby a coolant flow path is defined between the insulating plate and the cooling tube adjacent the bypass tube. In a further form, an untraversed enclosed space is defined between the insulating plate and the bypass tube, and the closure blocks coolant from the untraversed enclosed space. In a still further form, the untraversed space has heat-insulating properties.  
         [0020]     In another form of this aspect, the insulating plate includes an end protruding beyond the stack of flat tubes, and the protruding end cooperates with the switching valve. In a further form, the switching valve includes a flap, and the flap cooperates with the insulating plate end to either close the cooling tubes in the bypass position or close the bypass tube in the cooling position.  
         [0021]     In still another form of this aspect, the switching valve includes a flap having an axis substantially in the plane of the insulating plate.  
         [0022]     In one aspect of the present invention, a housingless heat exchanger is provided, including a stack of flat tubes with at least two of the tubes being cooling tubes and at least one of the flat tubes being a bypass tube, and at least one collecting tank on one end of the stack of flat tubes for gas streaming in the tube flow paths. Each of the flat tubes comprise a pair of plates connected to define a flow path therethrough, and an enclosed space is defined between adjacent flat tubes. Coolant inlet and outlet channels are formed by connected openings in the plates, with the channels being hydraulically connected to the enclosed space between the cooling tubes whereby coolant flows through the enclosed space between the cooling tubes. A switching valve in the collecting tank is movable between a cooling position in which at least most of the gas streams through the cooling tubes and a bypass position in which at least most of the gas streams through the bypass tube. An insulating plate is between the bypass tube and the cooling tube adjacent the bypass tube, the insulating plate blocking heat exchange between coolant and the bypass tube.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     The invention is described herein via practical examples, with written descriptions and the following figures.  
         [0024]      FIG. 1  is a perspective exploded view of one embodiment of a heat exchanger according to the present invention;  
         [0025]      FIG. 2  is a top view of the heat exchanger of  FIG. 1 ;  
         [0026]      FIG. 3  is a transverse cross-section through the heat exchanger of  FIG. 1 ;  
         [0027]      FIG. 4  is a transverse cross-section similar to  FIG. 1  but showing an alternate embodiment;  
         [0028]      FIG. 5  is a longitudinal cross-section through a heat exchanger having an insulating plate according to one embodiment of the present invention; and  
         [0029]      FIG. 6  is a longitudinal cross-section through a heat exchanger without insulation plate according to another embodiment of the present invention. 
     
    
       [0030]     Additional features and advantages which prove to be particularly important are apparent from this description.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     A housingless exhaust heat exchanger  10  embodying to the present invention is variously shown in the Figures. In the illustrated exemplary embodiment, the heat exchanger  10  is for use with a vehicle cooled by the coolant (preferably liquid) of the internal combustion engine.  
         [0032]     In the illustrated embodiment, the heat exchanger  10  includes three flat tubes  14 ,  16 ,  18 , each of which is advantageously formed of a pair of deformed plates  20 ,  22  suitably joined along their generally longitudinal edges  26 . The plates  20 ,  22  also have a peripheral contoured section  30  with a recessed face  32  surrounded by a peripheral lip  34 , such as described in EP 992 756 B1, the disclosure of which is hereby fully incorporated by reference. EP Application 03 007 724.2 (EP Publication 1 376 043 A2) also discloses features of a housingless heat exchanger which may be used with the present invention, the disclosure of which is hereby also fully incorporated by reference.  
         [0033]     The flat tubes  14 ,  16 ,  18  are stacked one on the other, with the contoured section  30  on the bottom (according to the  FIG. 1  orientation) of the plate  22  of the top tube  14  abutting the contoured section  30  on the top of the plate  20  of the middle tube  16 , and the contoured section  30  on the bottom (according to the  FIG. 1  orientation) of the plate  22  of the middle tube  16  abutting the contoured section  30  on the top of the plate  20  of the bottom tube  18 . Flow channels are defined between selected contoured sections as further described below.  
         [0034]     Only three flat tubes  14 ,  16 ,  18  are shown in the practical example. It should be understood, however, that other numbers of such tubes could be used in heat exchangers incorporating the present invention, with the number of flat tubes  14 ,  16 ,  18  chosen, for example, according to the performance requirements of the heat exchanger  10 . As will be apparent from the further description below, two of the flat tubes  14 ,  16  are cooled and one of the flat tubes  18  is not cooled. It is expedient to provide the cooled or cooling flat tubes  14 ,  16  with a suitable internal insert  40  such as is known in the art (e.g., a serpentine fin) as indicated in  FIG. 3 .  
         [0035]     At one end of the stack of flat tubes  14 ,  16 ,  18 , a collecting tank  44  is arranged in the fashion of a diffusor, and another collecting tank  46  (see  FIG. 6 ) is provided on the other end of the tube stack. The two collecting tanks  44 ,  46  may be identical, apart from the differences caused by the switching valve  50 , which are explained further below. The exhaust (or charge air, depending upon the system with which the heat exchanger  10  is used) will thus selectively flow (based on the switching valve  50 ) through flow paths in the flat tubes  14 ,  16 ,  18  as described below. EP Application 03 007 724.2 (EP Publication 1 376 043 A2) also discloses diffuser features which may be used with the present invention. The disclosure of the EP Application has already been fully incorporated by reference herein.  
         [0036]     Coolant, which may be selectively used to cool the exhaust as described below, may be directed through an inlet connector  56  to inlet channels  60  defined by openings in side flanges of the plates  20 ,  22 . The inlet channels  60  are aligned as further described below, whereby coolant from the inlet connector  56  may pass through the inlet channels  60  and, from there, to flow channels  64 ,  66 ,  68  defined at the contoured sections  30  of the plates  20 ,  22 .  
         [0037]     Housingless heat exchangers of this general type have been shown, for example, in German application DE 102 29 083.0, European application EP 03 007 724.2 (EP Publication 1 376 043 A2), and EP 992 756 B1, the disclosures of which are all hereby fully incorporated by reference. Such heat exchangers are very compact and have very good functional properties.  
         [0038]     In the heat exchanger  10  of the present invention, perforations  72  that can be produced by metalworking are arranged around each inlet channel defining opening to connect the openings in the practical example. Inlet channels  60 , which pass through the heat exchanger  10  vertically (in the orientation shown in  FIG. 1 , with the tubes  14 , 16 , 18  horizontally oriented), may be suitably obtained by joining the perforations  72  (see  FIGS. 3 and 4 ).  
         [0039]     In the illustrated embodiment, one flow channel  64  is defined between the contoured section  30  of the top plate  20  of the top tube  14  and a cover plate  76  secured thereon. A second flow channel  66  is defined between the contoured sections  30  of the bottom plate  22  of the top tube  14  and the top plate  20  of the middle tube  16 . A third flow channel  68  is defined (in the  FIG. 3  embodiment) between the contoured section  30  of the bottom plate  22  of the middle tube  16  and an insulating plate  78  (described further below).  
         [0040]     The flow channels  64 ,  66 ,  68  outlet to outlet channels  80  which may be formed similarly to the inlet channels  60 , such channels  80  being aligned whereby coolant from each of the flow channels  64 ,  66 ,  68  may be discharged through an outlet connector  84 .  
         [0041]     It should thus be appreciated that coolant may advantageously flow (in the direction of solid arrows  86 ) through the flow channels  64 ,  66 ,  68  to cool exhaust passing (in the direction of dashed arrows  88 ) through the top and middle flat tubes  14 ,  16 . As indicated by the dashed arrows  88 , flow of the exhaust through the tubes  14 ,  16 ,  18  could be in either direction depending on design choices.  
         [0042]     The previously mentioned switching valve  50  may be advantageously installed, after soldering of the plates (e.g.,  20 ,  22 ,  76 ,  78 ) of the exhaust heat exchanger  10 , in two opposite openings  90 ,  92  in the wall  94  of collecting tank  44 . Bearing bushes  96 ,  98  for a rotatable shaft  100  are inserted and fastened in these openings  90 ,  92 , as shown in  FIG. 1 . A flap  104  is suitably secured to the rotatable shaft  100 , and a flap cooperating element  108  is also inserted into the collecting tank  44  in order to support the effect of flap  104 . That is, as is apparent from  FIG. 5 , the element  108  will define an opening whereby the flap  104  may be selectively moved between a bypass position blocking the top and middle tubes  14 , 16  (on the right in  FIG. 5 ) and a cooling position blocking the bottom tube  18  (on the left in  FIG. 5 ). Thus, the switching valve  50  may be advantageously used to selectively direct exhaust air (or at least most of the recirculating exhaust stream) through selected ones of the various tubes  14 ,  16 ,  18 , some of which are cooled and at least one of which (tube  18 ) is not cooled.  
         [0043]     The previously referenced insulating plate  78  is arranged between the cooled tubes  14 ,  16  and the at least one uncooled (bypass) flat tube  18 . The insulating plate  78  may be essentially flat and is connected on one side to a deformed plate  20  of the at least one uncooled flat tube  18  and on the other side to a deformed plate  22  of the adjacent cooled (middle) tube  16 . The insulating plate  78  is secured to the contoured section  30  of the two plates (plate  20  of tube  18  and plate  22  of tube  16 ). An untraversed space  112  having heat insulating properties is therefore left within the space between the insulating plate  78  and the deformed plates  20 ,  22  enclosed by the periphery of the contoured section  30  ( FIG. 3 ). The periphery of the contoured section  30  may be advantageously roughly U-shaped in cross-section, as is best shown in  FIGS. 3 and 4 .  
         [0044]     In addition to the cover plate  76 , the heat exchanger  10  may also advantageously have a base plate  118 , both also contoured and having a somewhat greater sheet thickness than the deformed heat exchanger plates  20 ,  22  in order to ensure additional stability. The base plate  118  and the cover plate  76  also include protrusions  122  for mounting a retainer bracket  126  for the switching valve  50  and control element  130 .  
         [0045]     As is apparent from the  FIG. 5  embodiment in which the insulating plate  78  separates the cooled ( 14 , 16 ) and uncooled ( 18 ) flat tubes, the end  130  of the insulating plate  78  may advantageously extend beyond the tube plates  20 ,  22  so as to cooperate with the switching valve flap  104 . The allows the flap  104  to be reduced in size, thereby minimizing the flap noises caused by flow of the exhaust and other functional disadvantages which can occur from a larger flap. The flap  104  can be reduced in size due to cooperation with the insulating plate end  130  and the flap cooperating element  108 , as is apparent from  FIG. 5 .  
         [0046]     The collecting tank  44  arranged in the fashion of a diffuser as previously noted, may advantageously have contoured sections  134  in its wall  94  ( FIG. 1 ) that are intended to accommodate two edges  136  each ( FIG. 4 ) on the end of the deformed plates  20 ,  22  of the flat tubes  14 ,  16 ,  18 . Because of this, the entire stack of flat tubes  14 ,  16 ,  18  is held together and soldering is made possible in a single operation without additional aids. Further details concerning this are described in EP application No. 03 007 724.2 (EP Publication 1 376 043 A2), the entire disclosure of which is hereby incorporated by reference.  
         [0047]      FIG. 3  is a cross-section through an exhaust heat exchanger of the type depicted in  FIG. 1  passing through both the inlet channel  60  and outlet channels  80  for coolant.  
         [0048]      FIG. 4  illustrates two different embodiments of the present invention. Specifically, as illustrated in the  FIG. 3  embodiment, the inlet and outlet channels  60 ,  80  may extend to both sides of the middle tube  16  whereby coolant may flow on both sides of the middle tube  16 , with the insulating plate  78  blocking the coolant from the contour section  30  of the bottom tube  18  and also itself serving as insulation to prevent cooling of exhaust air in the bottom tube  18  by the coolant. As schematically represented by reference numeral  140 , the insulating plate  78  may be omitted where closures  144  block the channels  60 ,  80 , as this blocks the coolant from reaching the space between the bottom and middle tubes  18 ,  16 . Suitable closures  144  include, for example, a member inserted into the corresponding perforation  72  surrounding the opening defining the channels  60 , 80 , or by not punching out the openings in one or more of the deformed plates  20 ,  22  of the middle tube  16 . Thus, it should be appreciated that the insulating plate  78  may therefore be dispensed with (but need not be) in the variant depicted in  FIG. 4 , although it is drawn in  FIG. 4 . The untraversed space  112  is larger in this embodiment than in the  FIG. 3  embodiment previously described.  
         [0049]      FIG. 6  is a longitudinal section through a heat exchanger according to  FIG. 4  (i.e., having closures  144  separating the cooled [ 14 ,  16 ] and uncooled [ 18 ] flat tubes). With no insulating plate  76  provided in this embodiment, a separate partition  150  may be provided to serve the previously described function of the insulating plate end  130 .  
         [0050]     Only practical examples in which the cooled and uncooled flat tubes  14 ,  16 ,  18  all consist of the same substantially the same deformed plates  20 ,  22  have been depicted herein. Such a construction has significant manufacturing advantages. However, it should be understood that it can be expedient to make the cooled flat tubes  14 ,  16  from plates different from those of the uncooled flat tube  18 , and that such structures would be within the scope of at least some facets of the present invention. Further, it should be understood that more flat tubes than illustrated, both for cooling and bypassing cooling, may also be provided within the scope of the present invention. Accordingly, it should further be appreciated that the present invention will provide advantageous design flexibilities.  
         [0051]     The present invention provides a heat exchanger which may be advantageously used, for example, for selected cooling of exhaust in a vehicle. Moreover, such heat exchangers may benefit from the advantages of housingless heat exchangers while at the same time providing such desirable selected operation, in a compact structure which may be easily manufactured at relatively low cost. For example, the entire heat exchanger  10  can be connected or produced in a single soldering operation, notwithstanding integrated switching valve  50 . The individual parts of the exhaust heat exchanger  10  may be easily combined by pushing the collecting tanks  44 ,  46  pushed over the ends of the flat tubes  14 ,  16 , 18 . Demanding welding operations, as are necessary in heat exchangers from the prior art, may thus be avoided.  
         [0052]     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.