Abstract:
A method of cooling exhaust gas (F) from an engine in an EGR cooler ( 10 ) for recirculation to the engine includes the steps of transporting the exhaust gas from the engine to a core assembly ( 22 ) disposed inside a single housing assembly ( 20 ), and dividing the housing assembly into at least a first cooling volume ( 42 ) of the EGR cooler ( 10 ) and a second cooling volume ( 44 ) of the EGR cooler ( 10 ). The core assembly ( 22 ) extends at least partially into the first cooling volume ( 42 ) and the second cooling volume ( 44 ). The method also includes the steps of introducing a first cooling fluid (CF 1 ) into the first cooling volume ( 42 ), and introducing a second cooling fluid (CF 2 ) into the second cooling volume ( 44 ). The exhaust gas (F) is transported from the core assembly ( 22 ) to the engine.

Description:
BACKGROUND 
       [0001]    Embodiments described herein relate generally to exhaust gas recirculation (EGR) systems in vehicles. More specifically, embodiments described herein relate to coolers used in EGR systems in vehicles. 
         [0002]    Exhaust gas recirculation (EGR) is used to reduce nitrogen oxide (NOx) emissions in both gasoline and diesel engines. NOx is primarily formed when a mix of nitrogen and oxygen is subjected to high temperatures. EGR systems recirculate a portion of an engine&#39;s exhaust gas back to the engine cylinders. Intermixing fresh, incoming air with recirculated exhaust gas dilutes the mix, which lowers the flame temperature and reduces the amount of excess oxygen. The exhaust gas also increases the specific heat capacity of the mix, which lowers the peak combustion temperature. Since NOx is more readily formed at high temperatures, the EGR system limits the generation of NOx by keeping the temperatures low. 
         [0003]    Most EGR systems include one or more EGR coolers either mounted to the engine or in fluid communication between an exhaust manifold and an intake manifold of an engine. Some engines, especially compression ignition or diesel engines, use the EGR cooler to cool the portion of exhaust gas being recirculated. The cooled exhaust gas has a lower latent heat content and can aid in lowering combustion temperatures even further. In general, engines using EGR to lower their NOx emissions can attain lower emissions by cooling the recirculated exhaust gas as much as possible. 
         [0004]    Some EGR systems have two EGR coolers, known as dual EGR coolers. The two EGR coolers have separate housings that are mounted in series in a spaced arrangement. The first EGR cooler reduces the temperature of the exhaust gas, and the second EGR cooler further reduces the temperature of the exhaust gas. Between the two EGR coolers there are typically funnel-shaped diffusers at the entrances and exits to the EGR coolers to direct the exhaust gas from the first EGR cooler to the second EGR cooler 
       SUMMARY OF THE INVENTION 
       [0005]    A method of cooling exhaust gas from an engine in an EGR cooler for recirculation to the engine includes the steps of transporting the exhaust gas from the engine to a core assembly disposed inside a single housing assembly, and dividing the housing assembly into at least a first cooling volume and a second cooling volume. The core assembly extends at least partially into the first cooling volume and the second cooling volume. The method also includes the steps of introducing a first cooling fluid into the first cooling volume, and introducing a second cooling fluid into the second cooling volume. The exhaust gas is transported from the core assembly to the engine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic section-view of a dual-stage EGR cooler having a single housing assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0007]    Referring now to  FIG. 1 , an EGR cooler is indicated generally at  10  and is configured to be incorporated in an EGR system (not shown) at the exhaust manifold (not shown) or in fluid communication between the exhaust manifold and an intake manifold (not shown) of an engine (not shown). The EGR cooler  10  receives a flow of exhaust gases F, such as from the exhaust manifold, at an inlet  12  of the EGR cooler and in the direction indicated in  FIG. 1 . The exhaust gases flow through the EGR cooler  10  to an outlet  14 . 
         [0008]    Between the inlet  12  and the outlet  14 , the exhaust gases are cooled in the EGR cooler  10  by a cooling fluid CF, for example engine coolant, as will be discussed in greater detail below. The exhaust gases may be cooled from about 1100-degrees Fahrenheit to about 300-degrees Fahrenheit, although other temperatures are contemplated. In the EGR cooler  10 , the exhaust gases are cooled in two stages, a first stage or higher-temperature stage, and a second stage or lower-temperature stage. In the direction of exhaust gas flow F, the exhaust gases are first cooled at the higher-temperature stage followed by the lower-temperature stage. 
         [0009]    A first or high-temperature radiator  16  of the EGR cooler  10  forms the first stage, and is upstream of a second or low-temperature radiator  18  of the EGR cooler  10  that forms the second stage. It is possible that additional radiators may be incorporated into the EGR cooler  10 . The first or high-temperature radiator  16  and the second or low-temperature radiator  18  are housed in a single housing assembly  20 . Locating both the first or high-temperature radiator  16  and the second or low-temperature radiator  18  in the same housing assembly  20  reduces potential flow restrictions of the exhaust gas F, as compared to the conventional dual EGR cooler configuration where individual cooler housings are provided in series. Further, the single housing assembly  20  may be lighter and less costly than providing two or more individual cooler housings. 
         [0010]    The EGR cooler  10  has a core assembly  22  that extends into both the first or high-temperature radiator  16  and the second or low-temperature radiator  18 . The flow of exhaust gas F is within the core assembly  22 , which extends generally from the inlet  12  to the outlet  14 . Alternatively, the core assembly  22  may extend substantially the distance between the inlet  12  and the outlet  14 . 
         [0011]    The core assembly  22  is generally elongate and has a rectangular shape in transverse cross-section, however other shapes are possible. The core assembly  22  includes a plurality of tube-and-fin assemblies  24  that provide fluid communication of the exhaust gas flow F through the core assembly  22 . The tube-and-fin assemblies  24  may be formed of stainless steel, or any other highly corrosion-resistant material. It is possible that the tube-and-fin assemblies  24  may have a spaced arrangement to permit the cooling fluid CF to flow in the spaces between the tube-and-fin assemblies  24 . 
         [0012]    The housing assembly  20  is generally elongate and rectangular in transverse cross-section, and has first and second side members  26 ,  28  that are generally parallel with the core assembly  22 . Third and fourth side members (not shown) are generally similar to first and second side members  26 ,  28  but are generally disposed perpendicularly to the first and second side members to form the generally rectangular shape of the housing assembly  20 . 
         [0013]    End caps  30 ,  32  are generally perpendicular to the core assembly  22 . To form the housing assembly  20 , the side members  26 ,  28  are attached to the end caps  30 ,  32  with fasteners  34 . A first seal  36  is provided at the attachment of the end cap  30  to the side members  26 ,  28 , and a second seal  38  is provided at the attachment of the end cap  32  to the side members  26 ,  28 . It is possible that the housing assembly  20  can have a configuration other than generally rectangular. 
         [0014]    A collar  40  is disposed generally transverse to the core assembly  22 , and separates the first or high-temperature radiator  16  from the second or low-temperature radiator  18 . The collar  40  may be brazed or otherwise sealingly attached to the core assembly  22 , and sealed to the housing assembly  20  to form a first cooling fluid volume  42  and a second cooling fluid volume  44 . A first radiator inlet  46  to the first cooling fluid volume  42  is disposed on a first side member  26 , and a first radiator outlet  48  is disposed on a second side member  28 . A second radiator inlet  50  of the second cooling volume  44  is disposed on a first side member  26 , and a second radiator outlet  52  is disposed on a second side member  28 . The cooling fluid CF can either have a parallel flow or a counterflow arrangement. 
         [0015]    The collar  40  is mounted within the housing assembly  20  with a seal mount  54 , which is attached to the side members  26 ,  28 . The seal mount  54  includes a seal  56 , such as an O-ring, and mount members  58  attached to an interior surface of the side members  26 ,  28 . The seal  56  is located between the mount member  58  and the collar  40 . The collar  40  may have an extension portion  41  that engages the mount member  58 . In this configuration, the core  22  does not contact the side members  26 ,  28  of the housing assembly  20 , but has a “floating” configuration. Alternatively, the collar  40  may be brazed to the interior surface of the housing assembly  20 . 
         [0016]    Exhaust gas F flows through the inlet  12  of the core assembly  22 , which is an opening located at the end cap  30 . An entrance diffuser  60  may be attached to the inlet  12  of the core assembly  22 . The entrance diffuser  60  may be located at the exterior, the interior or partially to the interior/exterior of the housing assembly  20 . The entrance diffuser  60  may have a diffuser inlet  62  that receives the flow of exhaust gas F. The exhaust gas F flows through diffuser inlet  62 , through the entrance diffuser  60 , through the inlet  12  and through the core assembly  22 . An outlet diffuser  64  fluidly connects the core assembly  22  to the outlet  14 . 
         [0017]    The end cap  32  may have a two-piece assembly, for example having a first adapter  66  and a second adaptor  68 , which therebetween receives the outlet diffuser  64 . The adapters  66 ,  68  maintain the core assembly  22  in the floating configuration within the housing assembly  20 . A seal  70 , such as an O-ring, seals the cooling fluid CF within the second cooling fluid volume  44 . 
         [0018]    The cooling fluid CF 1  flows through the first or high-temperature radiator  16  between the housing assembly  20  and the core assembly  22 , and in the case where the tube-and-fin assemblies  24  have a spaced relationship, between the tube-and-fin assemblies. The collar  40  seals the flow of cooling fluid CF within the first or high-temperature radiator  16 . At the first radiator inlet  46  of the first or high-temperature radiator  16 , the cooling fluid is about 220-degrees Fahrenheit, however other temperatures are contemplated. 
         [0019]    Cooling fluid CF 2  flows though the second or low-temperature radiator  18  between the housing assembly  20  and the core assembly  22 , and in the case where the tube-and-fin assemblies  24  have a spaced relationship, between the tube-and-fin assemblies. The collar  40  seals the flow of cooling fluid CF within the second or low-temperature radiator  18 . At the second radiator inlet  50  of the second or low-temperature radiator  18 , the cooling fluid is about 110-degrees Fahrenheit, however other temperatures are contemplated. The second cooling fluid CF 2  has a lower temperature than the first cooling fluid CF 1 . 
         [0020]    It is possible that the collar  40  is brazed to the tube-and-fin assemblies  24 , the outlet diffuser is brazed to the tube-and fin assemblies, and the end cap  30  is brazed to the tube-and-fin assemblies to form a core assembly  22 . The core assembly  22  is received by the adaptors  66 ,  68  of the end cap  32  as the core assembly is mounted and sealed within the housing assembly  20 . The side members  26 ,  28  are attached to the end caps  30 ,  32 . 
         [0021]    It is possible that the EGR cooler  10 , including the housing assembly  20  and the core assembly  22 , are formed of corrosion resistant alloys that help protect the EGR cooler from the corrosive exhaust gases.