Abstract:
An exhaust gas recirculation cooler for internal combustion engines and a method of forming same. One or more cooler tubes incorporate a flexible section, comprised of one or more integrally formed convolutions, with a tube and fin architecture. The exhaust gas recirculation cooler provides thermal compensation, on a per-tube basis, with the flexible sections of the one or more cooler tubes individually displacing upon the thermal expansion of any of the respective tubes.

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to exhaust gas recirculation systems for internal combustion engines, in particular, exhaust gas recirculation coolers. 
     BACKGROUND OF THE DISCLOSURE 
     Modem internal combustion engines have, for many years, been equipped with exhaust gas recirculation mechanisms for routing exhaust gas from their own internal combustion processes back into their intake manifolds, in order to increase efficiency and/or limit the production of undesirable exhaust components, such as nitrogen oxide. For example, introducing exhaust gas into a combustion mixture in an engine&#39;s cylinder is known to lower the combustion temperature and, in turn, reduce the formation of nitrogen oxide, as nitrogen oxide forms at elevated temperatures. In order to reduce those elevated temperatures, it is known to cool exhaust gas before introducing it to the combustion mixture. While typical exhaust gas recirculation cooler applications reduce the temperature of exhaust gas from 650° C. to 120° C., the specific cooling requirements for the recirculated gases will often vary according to engine size, type and application. 
     Typical exhaust gas recirculation coolers are coupled to the internal combustion engine&#39;s overall cooling system, and pass exhaust gas through cooling tubes, which are cooled by the engine&#39;s radiator coolant. Exhaust gas recirculation coolers have proven to be some of the most complex and historically unreliable pieces of a modern internal combustion engine. These issues have only been exacerbated by the increase in importance as focus has increased on emissions performance and the efficiency of internal combustion engines. 
     Exhaust gas recirculation coolers must operate under two primary loading mechanisms—thermal fatigue and thermal shock. Thermal fatigue refers to the thermal stresses encountered by exhaust gas recirculation coolers during normal operation. Thermal shock refers to abnormal operating conditions of exhaust gas recirculation coolers, such as the loss of coolant through broken pumps, cooling line failure, etc. Thermal shock is often accompanied by metal expansion of longitudinally oriented exhaust gas recirculation cooler components. 
     Metal expansion during thermal shock in an exhaust gas recirculation cooler may cause the exhaust gas recirculation cooler to rupture or leak, which, in turn, may negatively impact the overall engine performance. With a cooler leak, coolant may enter the path of the recirculated exhaust gas—back into the intake manifold and, ultimately, the engine cylinder. Any coolant in the engine cylinders impedes the engine&#39;s performance and, at certain levels, may completely inhibit the cylinders from firing. Furthermore, if coolant is leaking out of an exhaust gas recirculation cooler, the engine&#39;s overall cooling system is affected by that coolant loss. Finally, a leaking exhaust gas recirculation cooler itself may fall to perform its own function—that is to cool the exhaust gases being recirculated to the intake manifold. As set forth above, an elevated temperature of the combustion mixture may lead to undesirable engine and emissions performance. 
     Two styles of exhaust gas recirculation cooler are known to provide thermal compensation features which accommodate some metal expansion to resist such failure during extreme thermal shock operating conditions. First, it is known for exhaust gas recirculation coolers to employ round, corrugated or convoluted, hollow cooling tubes, which bow and flex to accommodate metal expansion. However, such hollow, round, corrugated tubes have power density limitations, that is, a relatively limited ability to cool exhaust gases passing therethrough, for a given size of tube, as compared to other known constructions for cooler tubes. 
     Second, it is known to employ floating cores with cooler tubes with relatively higher power density capabilities, such as those with a tube and fin architecture. Cooling tubes with a tube and fin architecture are relatively flattened or oval shaped, with a fin structure bonded inside of a tube, creating an extremely stiff assembly—which expands without compromise under thermal shock conditions. A floating core approach is known to provide a two-piece exhaust manifold, jointly coupled to all of the cooling tubes, which two pieces are movably coupled with an O-ring connection. When the cooling tubes expand, the exhaust manifold components can move relative to each other along the O-ring connection. Such a macro-compensating feature is limited in its effectiveness, however, as exhaust gas recirculation coolers typically do not experience thermal shock on a uniform, macro-scale. Rather, thermal shock conditions typically result in non-uniform expansion of cooling tubes. 
     Accordingly, an exhaust gas recirculation cooler with relatively high power density and improved thermal shock performance is desirable. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides an improved exhaust gas recirculation cooler comprising an elongated, hollow main body, first and second end plates coupled to opposing ends of the main body, and at least one cooler tube assembly coupled between the first and second end plates. The at least one cooler tube assembly includes an elongated tube member with a substantially oval cross-sectional shape and a fin sheet extending into at least a portion of the tube member. The at least one tube member has at least a first convolution integrally formed therein, the first convolution defining a relatively flexible section of the at least one cooler tube assembly. The tube member and the fin sheet are restrainably bonded within a relatively rigid section of the at least one cooler tube assembly, separate from and integrated with the relatively flexible section of the at least one cooler tube assembly. The relatively flexible section of the at least one cooler tube assembly displaces upon thermal expansion of the at least one cooler tube assembly, to limit mechanical stresses in the first and second end plates. 
     The improved gas recirculation cooler further comprises a plurality of cooler tube assemblies coupled between the first and second end plates and spaced apart from one another. The plurality of cooler tube assemblies each include an elongated tube member with a substantially oval cross-sectional shape and a fin sheet extending into at least a portion of the tube member. The plurality of elongated tube members further include at least a first convolution integrally formed therein, the first convolution of each the tube member defining a relatively flexible section of the respective cooler tube assembly. Each tube member of the plurality of tube members including a fin sheet that is restrainably bonded within a relatively rigid section of the cooler tube assembly, separate from and integrated with the relatively flexible section of the respective tube assembly. The relatively flexible section of the respective cooler tube assembly displaces independently from the remainder of the plurality of cooler tube assemblies upon thermal expansion of the respective cooler tube assembly, to limit the mechanical stresses generated within the first and second respective end plates. 
     In some preferred embodiments, the tube member has a plurality of convolutions integrally formed therein, the plurality of convolutions defining the relatively flexible section of the at least one cooler tube assembly. 
     In some preferred embodiments, the tube member has a first thickness at the relatively rigid section of the at least one cooler tube assembly and the tube member has a second thickness at the first convolution, and the first thickness and the second thickness are substantially equal. 
     In some preferred embodiments, the first convolution is proximate a first end of the tube member. 
     The improved gas recirculation cooler further comprises an exhaust inlet coupled to a first end of the at least one cooler tube assembly for conducting flow on exhaust gas. The exhaust inlet is configured for coupling to the exhaust manifold of an internal combustion engine. The improved gas recirculation cooler further comprises an exhaust outlet coupled to a second end of the at least one cooler tube assembly at a position substantially opposite the first end. The exhaust outlet is configured for coupling to the intake manifold of an internal combustion engine. 
     The improved gas recirculation cooler further comprises a coolant inlet and a coolant outlet. The coolant inlet and the coolant outlet are configured for coupling to the coolant system of an internal combustion engine. The main body further includes a coolant inlet aperture fluidly coupled to the coolant inlet and a coolant outlet aperture fluidly coupled to the coolant outlet, such that coolant travels generally longitudinally through the main body between the coolant inlet and the coolant outlet. 
     In some preferred embodiments, the tube member is fabricated of stainless steel. 
     In some preferred embodiments, the tube member and the fin sheet are restrainably bonded to one another through a braised attachment interface. 
     The present disclosure also provides a method for forming an improved exhaust gas recirculation cooler, comprising forming an elongated tube with a substantially oval cross-sectional shape; integrally forming at least a first convolution in the tube to define an integrated flexible tube portion; inserting a fin sheet within the tube, in a position spaced longitudinally apart from the flexible tube portion; restrainably bonding the relative positioning of the fin sheet within the tube; and coupling the tube substantially between opposing ends of a cooler case with the flexible tube portion positioned proximate to one of the opposing ends of the cooler case. The flexible tube portion of the tube displaces upon the thermal expansion of the tube. 
     The method for forming an improved exhaust gas recirculation cooler further comprises substantially maintaining the thickness of the tube at the first convolution. 
     In some preferred embodiments, restrainably bonding the tube and the fin sheet includes braising the fin sheet within the tube. 
     In some preferred embodiments, integrally forming at least the first convolution in the tube to define the integrated flexible tube portion includes mechanically bulging the first convolution. 
     The method for forming an improved exhaust gas recirculation cooler further comprises successively integrally forming a second convolution in the tube, the first and second convolutions collectively defining the integrated flexible tube portion. 
     The method for forming an improved exhaust gas recirculation cooler further comprises contemporaneously integrally forming at least the first convolution and a second convolution in the tube, the first and second convolutions collectively defining the integrated flexible tube portion. 
     In some preferred embodiments, integrally forming at least the first convolution in the tube to define the integrated flexible tube portion includes hydroforming of the first convolution. 
    
    
     
       BRIEF DESCRIPTION Of THE DRAWINGS 
         FIG. 1  of the drawings is a perspective view of an elongated oval cooler tube according to the principles of the present disclosure; 
         FIG. 2  is a perspective view of an elongated oval cooler tube with one convolution formed therein according to the principles of the present disclosure; 
         FIG. 3  is a perspective view of an elongated oval cooler tube with three convolutions formed therein according to the principles of the present disclosure; 
         FIG. 4  is a perspective view of an elongated oval cooler tube with five convolutions formed therein according to the principles of the present disclosure; 
         FIG. 5A  is an elevated end view of an elongated oval cooler tube with five convolutions formed therein according to the principles of the present disclosure; 
         FIG. 5B  is a side cross-sectional view of the elongated oval cooler tube of  FIG. 5A  taken along line A-A of  FIG. 5A  and looking in the direction of the arrows of line A-A; 
         FIG. 5C  is a top plan cross-sectional view of the elongated oval cooler tube of  FIG. 5B  taken along line C-C of  FIG. 5C  and looking in the direction of the arrows of line C-C; 
         FIG. 5D  is an enlarged cutaway view of the portion of the elongated oval cooler tube of  FIG. 5B  inside circle B of  FIG. 5B ; 
         FIG. 6A  is a perspective view of a fin sheet according to the principles of the present disclosure; 
         FIG. 6B  is a perspective view of an alternative fin sheet according to the principles of the present disclosure; 
         FIG. 7A  is an elevated and view of an elongated oval cooler tube, fin sheet and film assembly according to the principles of the present disclosure; 
         FIG. 7B  is an elevated side cross-sectional view of the elongated oval cooler tube, fin sheet and film assembly of  FIG. 7A  taken along line A-A of  FIG. 7A  and looking in the direction of the arrows of line A-A; 
         FIG. 7C  is a top plan cross-sectional view of the elongated oval cooler tube, fin sheet and film assembly of  FIG. 7B  taken along line B-B of  FIG. 7C  and looking in the direction of the arrows of line B-B; 
         FIG. 7D  is an enlarged cutaway view of the portion of the elongated oval cooler tube, fin sheet and film assembly of  FIG. 7A  inside circle C of  FIG. 7A ; 
         FIG. 8  is a perspective view of an exhaust gas recirculation cooler assembly according to the principles of the present disclosure; 
         FIG. 9  is a perspective view of an assembly of elongated oval cooler tubes for an exhaust gas recirculation cooler according to the principles of the present disclosure; 
         FIG. 10A  is an elevated end view of the assembly of cooler tubes of  FIG. 9 ; 
         FIG. 10B  is a side cross-sectional view of the assembly of cooler tubes of  FIG. 10A  taken along the line A-A of  FIG. 10A  and looking in the direction of the arrows of line A-A; and 
         FIG. 10C  is a top plan cross-sectional view of the assembly of cooler tubes of  FIG. 10B  taken alone line B-B of  FIG. 10B  and looking in the direction of the arrows of line B-B. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is further described with reference to the accompanying drawings, which show particular embodiments of the disclosure. However, it should be noted that the accompanying drawings are merely exemplary. For example, the various elements and combinations of elements described below and illustrated in the drawings can vary to result in embodiments which are still within the spirit and scope of the present disclosure. 
     With reference to  FIGS. 8-10 , exemplary exhaust gas recirculation cooler  20  includes main body  22  and first and second end plates  24 ,  26  encasing cooler tube assemblies  30 , which are arranged in an array in the illustrated embodiment. Exhaust gas recirculation cooler  20  is capable of being coupled to the exhaust manifold of an internal combustion engine via exhaust inlet  36 , and is configured to direct the exhaust gases back toward the engines intake manifold via exhaust outlet  38 , after the exhaust gases pass through cooler tube assemblies  30 . It should be understood that, according to the principles of the present disclosure, exhaust gas recirculation cooler  20  can include a single cooler tube assembly  30  or a varying number of cooler tube assemblies  30 , which components may be arranged in a variety of configurations. Thus, it should be understood that the particular configuration of the exhaust gas recirculation cooler  20  of the present disclosure is exemplary in nature. 
     Exhaust gas recirculation cooler  20  is configured to operate with a coolant system via coolant inlet  40  and coolant outlet  42 . Coolant is delivered from the coolant system to coolant inlet  40  and enters main body  22  through coolant inlet apertures  44 . The coolant travels generally longitudinally through main body  22 , drawing heat from cooler tube assemblies  30  and the exhaust gases passing therethrough. Coolant exits main body  22  through coolant outlet aperture  46  and is directed back into the coolant system via coolant outlet  42 . It should be understood that, according to the principles of the present disclosure, exhaust gas recirculation cooler  20  can be configured to operate with a wide variety of internal combustion engines, including gasoline and diesel engines, and the particular components and systems thereof, such as coolant systems, and, thus, the particular configuration of the exhaust gas recirculation cooler  20  of the present disclosure is exemplary in nature. 
     With further references to  FIGS. 4-5 , each cooler tube assembly  30  of exhaust gas recirculation cooler  20  includes a tube  50 . Tube  50  is an elongated hollow tube extending between first and second ends  52 ,  54  and having a substantially oval shaped cross-section. Proximate first end  52 , one or more convolutions  56  are integrally formed in tube  50 . The one or more convolutions  56  constitute the integral, relatively flexible portion  58  of tube  50 . The substantial, integral remainder of tube  50  constitutes the main cooling portion  60  thereof. Preferably, tube  50  comprises stainless steel. 
     With further reference to  FIGS. 1-4 , the formation of tube  50 , according to the principles of the present disclosure, is illustrated. As shown in  FIG. 1 , tube  50  begins as an elongated, substantially oval tube with no convolutions. In one preferred embodiment, as shown in  FIG. 2 , a first convolution  56  is integrally formed in tube  50  spaced apart from first end  52 . As shown in  FIGS. 3-4 , successive convolutions  56  are formed, one after another, each being positioned closer towards first end  52 . A preferred method of conducting such a successive, integral formation of convolutions  56  in tube  50  is through mechanical bulging of tube  50 . As illustrated in detail in  FIG. 5D , convolutions  56  are preferably formed such that the wall thickness  62  of cooling portion  60  of tube  50  is substantially similar or equal to the wall thickness  64  of convolutions  56 . 
     It should be understood than the method of forming convolutions  58  in tube  50  can vary according to the principles of the present disclosure. For example, in another preferred embodiment, multiple convolutions  56  are formed simultaneously through hyrdoforming. 
     Referring to  FIG. 6A , exemplary fin sheet or fin module  66  of cooler tube assembly  30  is a relatively thin material which defines sets of longitudinal channels  68 ,  70  by a laterally alternating U-shaped configuration. Specifically, the upward facing U-shaped portions of fin sheet or fin module  66  define channels  68 , the downward facing U-shaped portions of fin sheet  66  define channels  70 , and channels  68 ,  70  alternate laterally across fin sheet  66 . Referring to  FIG. 6B , an alternative fin sheet or fin module  66 ′ is illustrated, in which includes longitudinal undulations formed in the sheet. 
     Referring to  FIGS. 7A-7D , an exemplary cooler tube assembly  30  includes fin sheet  66  and coupling film  72  (see  FIG. 7D , in which the components are spaced apart for illustration purposes) inserted info tube  50 , and positioned within main cooling portion  60  of tube  50 . If should be understood that multiple sheets of coupling film  72  are positioned on opposing sides of fin sheet  66  between fin sheet  66  and tube  50 , so as to provide an attachment interface between tube  50  and fin sheet  66  and to enable bonding of tube  50  and fin sheet  66  through braising or a similar process. When fin sheet  66  is bonded to tube  50 , channels  68 ,  70  of fin sheet  66  define alternating channels within main cooling portion  60  of tube  50 . As particularly illustrated in  FIGS. 7B and 7C , in a preferred embodiment of the present disclosure, fin sheet  66  is located within main cooling portion  60  of tube  50  and does not extend into flexible portion  58  of tube  50 . Fin sheet  66  and main cooling portion  60  of tube  50  collectively comprise tube and fin section  72  of cooler tube assembly  30 , while flexible portion  58  of tube  50  comprises flexible section  74  of cooler tube assembly  30 . As tube and fin section  72  preferably constitutes substantially more of cooler tube assembly  30  than flexible section  74 , cooler tube assembly  30  imparts the known relatively high power density—greater temperature reduction per a given volume—characteristics of tube and fin architecture to exhaust gas recirculation cooler  20 . 
     With further reference to  FIGS. 10A-10C , exhaust gas recirculation cooler  20  a plurality of cooler tube assemblies  30  encased by main body  22  and first and second end plates  24 ,  26 . Cooler tube assemblies  30  are respectively received in tube apertures  80  of first end plate  24  and tube apertures  82  of second end plate  28 . In a preferred embodiment of the present disclosure, the components of individual cooler tube assembles  30 , as well as cooler tube assemblies  30  and first and second end plates  24 ,  26 , respectively are permanently bonded to one another contemporaneously, such as in a single braising process. 
     With particular reference to  FIGS. 10B and 10C , cooler tube assemblies  30  are spaced apart within main body  22 , so that coolant may travel in between cooler tube assemblies  30  and assist in transferring heat from exhaust gases passing through cooler tube assemblies  30 . Additionally, according to the principles of the present disclosure, upon thermal expansion of cooler tube assemblies  30 , such as under abnormal, thermal shook operating conditions for exhaust gas recirculation cooler  20 , each individual cooler tube assembly  30  can be displaced at its respective flexible section  74  to accommodate expansion occurring in that cooler tube assembly  30 —independent of the other cooler tube assemblies. The displacement of any individual cooler tube assembly  30  at its respective flexible section  74  limits the forces exerted by that cooler tube assembly  30  on first and second end plates  24 ,  26 , and thus the stresses in first and second end plates  24 ,  26 , during thermal expansion of that cooler tube assembly  30 . 
     By limiting the forces exerted by any individual cooler tube assembly  30  on first and second end plates  24 ,  26  during thermal expansion of that cooler tube assembly  30 , exhaust gas recirculation cooler  20  inhibits coolant leaking which may arise out of a failure or crack at first and second end plates  24 ,  26 —and thus helps prevent decreases in engine performance, decreases in cooling system performance, and/or decreases in exhaust gas recirculation performance. Moreover, as each individual cooler tube assembly  30  can be displaced at its respective flexible section  74  independent of the other cooler tube assemblies, exhaust gas recirculation cooler  20  is capable of responding to a relatively wide range of thermal shock conditions—which are typically non-uniform in nature and, thus, require varied performance across exhaust gas recirculation cooler  20 . 
     As exemplified herein, the present disclosure can vary in many ways. For example, if should be understood that an exhaust gas recirculation cooler according to the principles of the present disclosure can be used in a variety of constructions for a variety of vehicular applications. Additionally, the materials and shapes of the components of an exhaust gas recirculation cooler according to the principles of the present disclosure can vary, and remain within the scope of this invention. Accordingly, it is to be understood that the present disclosure is exemplary in nature.