Abstract:
An exhaust heat exchanger for an exhaust gas recirculation system, including a first flow path for the intake air for an internal combustion engine, a second flow path for the exhaust of an internal combustion engine, and a housing enclosing the first and second flow paths. The first and second flow paths are each divided into a plurality of flow channels in heat-conducting, metallically connected contact with each other, and the flow channels include elements promoting heat exchange between the flow channels.

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 relates to an exhaust heat exchanger for an exhaust gas recirculation system, and more particularly to an exhaust heat exchanger in which exhaust being returned for combustion again in the cylinder of an internal combustion engine is cooled by the intake air stream of the internal combustion engine.  
       BACKGROUND OF THE INVENTION AND TECHNICAL PROBLEMS POSED BY THE PRIOR ART  
       [0005]     Exhaust heat exchangers in exhaust gas recirculation systems often use the liquid coolant of the internal combustion engine to cool the exhaust gas. However, air that is heated in heat exchange with the exhaust and then used to heat the passenger compartment is often used in vehicle heating. An exhaust heat exchanger in an exhaust gas recirculation system is disclosed in U.S. Pat. No. 2,408,846, where the surrounding air cools exhaust air by flowing around the housing of the exhaust heat exchanger provided with cooling ribs on the outside. Also, DE 199 30 416 A teaches a cooling device in which the exhaust recirculation line is passed through the intake line of the internal combustion engine in order to cool the exhaust with the intake air.  
         [0006]     The present invention is directed toward improving upon exhaust heat exchangers which use intake air.  
       SUMMARY OF THE INVENTION  
       [0007]     In one aspect of the present invention, an exhaust heat exchanger for an exhaust gas recirculation system is provided, including a first flow path for the intake air for an internal combustion engine, a second flow path for the exhaust of an internal combustion engine, and a housing enclosing the first and second flow paths. The first and second flow paths are each divided into a plurality of flow channels in heat-conducting, metallically connected contact with each other, and the flow channels include elements promoting heat exchange between the flow channels.  
         [0008]     In one form of this aspect of the present invention, the flow channels of the second flow path are flat tubes assembled from two half shells. In a further form, the flat tubes have two openings in their broad sides and are stacked one on the other with a spacing therebetween with the one openings connected to each other to form an exhaust inlet channel, and the other openings connected to each other to form an exhaust outlet channel. In one still further form, the housing comprises a housing cap enclosing the stack of flat tubes and a metallic bottom plate to which the housing cap is secured, and the bottom plate has an inlet opening and an outlet opening for the exhaust, the inlet opening being connected to the exhaust inlet channel and the outlet opening being connected to the exhaust outlet channel. In another still further form, the flow channels of the first flow path are arranged in the spacing between the individual flat tubes. In yet another still further form, the exhaust inlet channel and the exhaust outlet channel have a non-circular shape favorable to flow in order to keep pressure loss on the intake air side low.  
         [0009]     In another form of this aspect of the present invention, the elements promoting heat exchange in the flow channels of the first flow path comprise corrugated ribs in heat-conducting contact with the flow channels of the second flow path.  
         [0010]     In still another form of this aspect of the present invention, the metallically connected contacts are joined by soldering.  
         [0011]     In yet another form of this aspect of the present invention, the housing comprises a housing cap enclosing the stack of flat tubes and a metallic bottom plate to which the housing cap is secured. In further forms, the housing cap is plastic, or the flow channels of the first flow path adjacent to one of the housing cap and the bottom plate include baffles. In another further form, the housing cap has an inlet and an outlet for intake air, and in a still further form the flat tubes are flattened, at least on the end facing the intake air inlet in the housing cap whereby pressure loss of the intake air is maintained low. In yet another further form, the housing cap has an edge which is mechanically connected to the bottom plate, and in a still further form at least one continuous recess is in the bottom plate in the vicinity of the edge.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a front view of the exhaust heat exchanger according to the present invention, without the housing cap;  
         [0013]      FIG. 2  is a side view of the heat exchanger of  FIG. 1 ;  
         [0014]      FIG. 3  is a cross-sectional view along line  3 - 3  of  FIG. 1 ;  
         [0015]      FIG. 4  is a top view of the heat exchanger of  FIG. 1 ;  
         [0016]      FIG. 5  illustrates the bottom plate of the exhaust heat exchanger;  
         [0017]      FIG. 6  is a perspective view of the exhaust heat exchanger of the present invention, with the housing cap and a schematic illustration of a system with which the heat exchanger may be used;  
         [0018]      FIG. 7  is a perspective view of a second embodiment of the heat exchanger according to the present invention;  
         [0019]      FIG. 8  is a cross-sectional illustration of the shape of an exhaust inlet channel; and  
         [0020]      FIG. 9  is a side view of the heat exchanger of  FIG. 7 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     An exhaust heat exchanger  10  according to the present invention is illustrated in  FIG. 1 , and includes flat tube-half shells  14 ,  16  with connected edge sections  18  to effectively form a flat tube  20  defining flow channels  22 . In the illustrated embodiment, both half shells  14 ,  16  are flattened on both opposite ends  26  so that a shape favorable for flow is created that leads to a limited pressure loss of the intake air flowing through flow channels  30 .  
         [0022]     Flow of intake air is illustrated by the dashed arrows  40  in  FIG. 1 , with the solid arrows  42  illustrating flow of exhaust. In the illustrated heat exchanger  10 , the flow path for the intake air is divided into four flow channels  30  and the flow path for the exhaust is divided into three flow channels  22 . However, it should be understood that the number of flow channels  22 ,  30  in itself is naturally not subject to any restrictions, although in the illustrated embodiment it may be advantageous (because of spatial conditions) to keep the number of flow channels  22 ,  30  low and to address higher performance requirements by, for example, longer flow channels  22 ,  30  and/or by altered flow patterns.  
         [0023]     The half shells  14 ,  16  forming the flat tubes  20  have two openings  46 ,  48 , with a collar  50  suitably molded onto the edge of the openings  46 ,  48  with a slightly conical design. The collars  50  of adjacent flat tubes are suitably secured together, for example, by inserting one into the other, so that an inlet channel  54  and an outlet channel  56  for the exhaust is created.  
         [0024]     A bottom plate  60  of the exhaust heat exchanger includes an inlet opening  62  and an outlet opening  64  that are aligned with the inlet channel  54  and the outlet channel  56 . The inlet opening  62  and the outlet opening  64  each have a corresponding collar  50  that can be combined with the collar  50  on the openings  46 ,  48  of the adjacent flat tube. A connection flange  70  applied to the bottom plate  60  lies on the same line for connection of an exhaust recirculation line only indicated (as illustrated schematically in  FIG. 6 ). A continuous recess  71  (see  FIGS. 3 and 5 ) may be advantageously provided in the bottom plate  60  to increase its rigidity, and further to slightly suppress heat conduction outward in the direction of housing cap.  
         [0025]     A spacing  72  remains between the flat tubes  20  in which the mentioned flow channels  30  for intake air are formed. Corrugated ribs  76  are situated in the intake air flow channels  30  and internal inserts  78  are inserted into the exhaust flow channels  22 . The wave direction of the corrugated ribs  76  may advantageously be across the flow direction of the intake air so that the intake air must flow through the channels  80  formed by the corrugated ribs  76 . At least the outer wave flanks of corrugated ribs  76  may be smooth and designed closed. Heat radiation to the housing or housing cap (which may be plastic) is therefore advantageously somewhat reduced.  
         [0026]     It should be appreciated that the internal inserts  78  may also be beads or the like molded into the broad sides  81  of the flat tubes.  
         [0027]     An advantageous design of the upper and lower (in the orientation of the figures) flow channels  30  for the intake air is particularly apparent from  FIGS. 2 and 3 , with the corrugated ribs  76  arranged in these two flow channels  30  each having a baffle  82  or  84  bent on the long edges  86 . These baffles  82 ,  84  on the one hand divert the intake air through the corrugated ribs  76  and on the adjacent flow channel  22  and therefore make heat exchange more intensive there. On the other hand, the baffles  82 ,  84  contribute to suppressing heat radiation outward in the direction toward the housing cap  90  (see  FIG. 6 ).  
         [0028]     It should be appreciated that the metallic individual parts of the exhaust heat exchanger  10 , like the corrugated ribs  76 , the flat tubes  20  (or preferably the flat tube half shells  14 ,  16 , the internal insert  78 , the bottom plate  60 , and the baffles  82 ,  84  may be advantageously made from an appropriate stainless steel sheet, suitably produced, for example, by deformation dies on deformation machines. The heat exchanger  10  may be manufactured by assembling these metallic parts and then joining them together in a soldering process.  
         [0029]     The exhaust heat exchanger  10  is illustrated in  FIG. 6  with the housing cap  90 , with an intake air inlet  92  and, on the other end, an air intake outlet  94 . The housing cap  90  may be advantageously mounted after the soldering process, with the edge  96  of the housing cap  90  mechanically connected to the edge of the bottom plate  60 . The connection is produced by deformation of protrusion  98  on the edge of bottom plate  60 . The bent protrusions  98  lie on a shoulder on the edge  96  of the housing cap  90  and secure the connection (see  FIG. 4 ). If desired and/or necessary, a seal may be provided in the connection.  
         [0030]     As previously noted, the housing cap  90  may be advantageously made of plastic, thereby assisting in desirably keeping the weight of the exhaust heat exchanger  10  low.  
         [0031]      FIG. 6  also illustrates an exemplary arrangement for exhaust recirculation with which the present invention may be used is illustrated, with input air and exhaust flow indicated by the dashed arrows  40  and the solid arrows  42 . The exhaust heat exchanger  10  according to the present invention may be advantageously incorporated into this type or into a differently-equipped exhaust gas recirculation system. In this example, after heat exchange with the exhaust in the heat exchanger  10 , the intake air then flows through a charge air cooler  110  before being introduced to the cylinders  114  of the internal combustion engine  118  as combustion air, mixed with the recirculated exhaust output from an EGR valve  120 . An exhaust valve flap  124  may be provided between the engine  118  and the exhaust inlet  62  of the heat exchanger  10  to divert exhaust either into the heat exchanger  10  or to recirculate directly back to the EGR valve  120 . In either case, the exhaust is recirculated for combustion again in the engine cylinders  114 . Arrows  42   a  illustrate recirculation lines for exhaust. Residual exhaust may also be output from the engine  118  through a turbocharger  124 .  
         [0032]      FIGS. 7-9  illustrate an alternate embodiment of a heat exchanger incorporating the present invention. It should be appreciated from this embodiment that the corrugated rib  76  of the outer (lower) intake air flow channel  20  may be connected directly to the bottom plate  60  (in which case, the lower baffle  82  (see  FIG. 3 ) may be left out.  
         [0033]     It is desirable that the cross-section of the inlet channel  54  and the outlet channel  56  for the exhaust be designed, to the extend possible, so that the pressure loss on the intake air side does not exceed a tolerable level. A favorable teardrop shape of the cross section in this respect between the flow paths  22  is schematically depicted in  FIG. 8 , with the channels  54 ,  56  created by joining the collars  50 , as previously discussed, with the collars being such a shape.  
         [0034]     It should thus be appreciated that the exhaust heat exchanger of the present invention does not operate using the coolant of the internal combustion engine but, in similar fashion to it, helps to improve exhaust recirculation (i.e., can contribute to reducing fuel consumption of the internal combustion engine and reducing emissions).  
         [0035]     Moreover, use of intake air as coolant as with the present invention is advantageous since operating situations of internal combustion engines, which often require no cooling of the exhaust, can be dealt with more easily. A simple air flap or bypass valve, which need not be integrated in the exhaust heat exchanger according to the present invention, is sufficient to send the intake air through the exhaust heat exchanger, or to divert it around it, depending upon the needs of the engine design. Since the intake air flowing through the intake line of the internal combustion engine has a relatively low temperature, an air flap operating as a bypass valve avoids the functional problems which can occur in integrated exhaust-bypass valves as a result of the extremely high temperatures in such other exhaust heat exchangers. However, it should be understood that the provision of bypass channels for the exhaust integrated in the exhaust heat exchanger is not absolutely necessary within the broad scope of some aspects of the present invention either.  
         [0036]     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.