Patent Publication Number: US-7581533-B1

Title: Three mode cooler for exhaust gas recirculation

Description:
TECHNICAL FIELD 
     This invention relates to cooling systems for exhaust gas recirculation in engines. 
     BACKGROUND OF THE INVENTION 
     Vehicles typically include an exhaust gas recirculation (EGR) system to selectively direct internal combustion engine exhaust gas to an air inlet of the engine. EGR can lower the level of certain undesirable engine emission components such as nitrogen oxide (NOx) and can improve fuel economy. Up to a limit, NOx emissions decrease with increasing EGR levels. Beyond the limit, EGR can increase formation of other undesirable engine emission components and can reduce vehicle drivability. 
     EGR typically involves recirculation of exhaust gas through an EGR passage between an engine exhaust conduit and an engine fresh air intake passage. A valve within the EGR passage (the EGR valve) is controlled to vary a restriction within the EGR passage to regulate the flow of exhaust gas therethrough. In compression ignition engines, recirculated exhaust gas may be cooled to enable induction of a greater mass of exhaust gas into the engine cylinders. 
     SUMMARY OF THE INVENTION 
     An exhaust gas recirculation system is provided for an engine having an exhaust manifold and an intake manifold. The system includes a valve assembly including a valve housing and at least one valve member. The valve housing defines a first port and a second port, and is operatively connectable to the engine such that the first port receives exhaust gas from the exhaust manifold and the second port is in fluid communication with the intake manifold. A heat exchanger defines a first passageway and a second passageway. The at least one valve member is selectively movable with respect to the valve housing to provide first, second, and third modes of operation. 
     In the first mode of operation, exhaust gas from the inlet port flows to the outlet port without flowing through either of the first and second passageways of the heat exchanger. In the second mode of operation, exhaust gas from the inlet port flows through the first and second passageways in series to the outlet port. In the third mode of operation, exhaust gas from the inlet port flows through the first and second passageways in parallel to the outlet port. 
     The first mode of operation provides a low resistance flow path for exhaust gas when EGR cooling is not desired. The second mode of operation provides a high degree of EGR cooling due to the longer effective flow path of exhaust gas through the heat exchanger compared to the third mode of operation. The third mode of operation provides EGR cooling with a lower flow restriction compared to the second mode. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic depiction of an engine including an exhaust gas recirculation system; 
         FIG. 2  is a schematic, sectional side view of the exhaust gas recirculation system of  FIG. 1  with a valve member in a first position; 
         FIG. 3  is a schematic, sectional side view of the exhaust gas recirculation system of  FIG. 1  with a valve member in a second position; and 
         FIG. 4  is a schematic, sectional side view of the exhaust gas recirculation system of  FIG. 1  with a valve member in a third position. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , an engine  10  includes an engine block  14 , which defines a plurality of cylinders (not shown). Each of the cylinders contains a respective piston (not shown), as understood by those skilled in the art. An intake manifold  18  is mounted with respect to the engine block  14  and defines a plurality of passageways that provide fluid communication between the cylinders and the atmosphere. Thus, the intake manifold  18  distributes air from the atmosphere to the cylinders. Intake valves (not shown) are operative to regulate the flow of air between the cylinders and the intake manifold  18 , as understood by those skilled in the art. 
     An exhaust manifold  22  is mounted with respect to the engine block  14  and is in selective fluid communication with the cylinders to receive exhaust gases therefrom. As understood by those skilled in the art, exhaust valves (not shown) are operative to regulate the flow of exhaust from the cylinders to the exhaust manifold  22 . In an exemplary embodiment, engine  10  is of the compression ignition type. 
     An exhaust gas recirculation (EGR) system  24  is configured to provide selective fluid communication between the exhaust manifold  22  and the intake manifold  18 . The EGR system  24  includes a valve assembly  26 . Referring to  FIGS. 1 and 2 , the valve assembly  26  includes a housing  28  that defines an inlet port  30  in fluid communication with the exhaust manifold  22  via conduit  34 . Accordingly, during operation of the engine  10 , the inlet port  30  receives exhaust gas from the exhaust manifold  22 . 
     The housing  28  also defines an outlet port  38  in fluid communication with the intake manifold  18  via conduit  42 . The housing  28  further defines a chamber  46  in fluid communication with the inlet port  30  and the outlet port  38 . A heat exchanger  50  is operatively connected to the valve assembly  26 . 
     Referring specifically to  FIG. 2 , the heat exchanger  50  defines a first passageway  54  and a second passageway  58 , which are divided by a wall  60 . The housing  28  further defines ports  62 ,  66 ,  70 . Passageway  54  provides fluid communication between port  66  and a chamber  74 . Passageway  58  provides fluid communication between port  62  and chamber  74 . Chamber  74  is defined by a rear header  78  mounted with respect to the heat exchanger  50 . The heat exchanger  50  is configured to transfer heat from exhaust gas in the passageways  54 ,  58  to a cooler fluid, such as water or air. Thus, the heat exchanger  50  cools exhaust gas as the exhaust gas flows through the passageways  54 ,  58 . Cooling fins  84  in passageways  54 ,  58  provide increased surface area for heat transfer between exhaust gas and the cooling fluid. Housing  28  and the heat exchanger  50  cooperate to define a passageway  86  that provides fluid communication between chamber  74  and port  70 , and thus passageway  86  provides selective fluid communication between chamber  74  and chamber  46 . 
     Chamber  46  provides selective fluid communication between all of the ports  30 ,  38 ,  62 ,  66 ,  70 . In the embodiment depicted, chamber  46  is generally circular in cross section. A butterfly valve member  90  is rotatably mounted with respect to the valve body  26  inside the chamber  46 , and is in sealing engagement with the wall  94  of the chamber  46 . The valve member  90  is movable between three positions to control fluid communication between the ports  30 ,  38 ,  62 ,  66 ,  70  such that the EGR system  24  is characterized by three modes of operation. 
     In a bypass mode of operation, shown in  FIG. 2 , the valve member  90  is in a first position in which the valve member  90  prevents fluid communication from the inlet port  30  to ports  62 ,  66 , i.e., EGR is prevented from flowing across the chamber  46  from the inlet port  30  to either of ports  62 ,  66 . In the first position, valve member  90  does not obstruct fluid flow from the inlet port  30  to the outlet port  38  via the chamber  46 . Accordingly, in the bypass mode of operation, exhaust gas  98  flows from the inlet port  30 , through the chamber  46 , to the outlet port  38 . Thus, in the bypass mode of operation, exhaust gas  98  does not flow through the heat exchanger  50  as it is transmitted from the exhaust manifold to the intake manifold. In the first position, the valve member  90  does not prevent fluid flow from the inlet port  30  to port  70 ; however, exhaust gas does not flow through the return passageway  86  because the valve member  90  deadheads ports  62 ,  66 . 
     In a dual pass mode of operation, shown in  FIG. 3 , valve member  90  is in a second position in which the valve member  90  obstructs fluid communication from port  70  to the chamber  46 . Valve member  90  directs flow in the chamber  46  from the inlet port  30  to port  66 , and from port  62  to the outlet port  38 . Valve member  90  obstructs flow across the chamber  46  from the inlet port  30  to port  62  and port  38 . Accordingly, when the valve member  90  is in the second position, exhaust gas  98  from the inlet port  30  flows through port  66 , then through the first passageway  54 , then through chamber  74 , then through the second passageway  58 , then through port  62 , to the outlet port  38 . Thus, during the second mode of operation, exhaust gas  98  that flows through the inlet port  30  flows through the first passageway  54  and the second passageway  58  consecutively. That is, exhaust gas  98  flows through passageway  54  and then through passageway  58  in series. 
     In a single pass mode of operation, shown in  FIG. 4 , valve member  90  is in a third position in which the valve member  90  prevents exhaust gas flow from the inlet port  30  to the outlet port  38  across the chamber  46 . Rather, valve member  90  directs exhaust gas  98  from the inlet port  30  across the chamber  46  to both port  62  and port  66 . Thus, some of the exhaust gas  98  that enters the chamber  46  from port  30  travels through passageway  54 , and some of the exhaust gas  98  that enters the chamber  46  from port  30  travels through passageway  58 . That is, exhaust gas  98  flows through passageway  58  and through passageway  54  in parallel. The direction of flow of exhaust gas  98  in passageway  58  in the third mode of operation is opposite the direction of flow in passageway  58  in the second mode of operation. 
     Exhaust gas  98  from the passageways  54 ,  58  enters chamber  74 , then flows through passageway  86  to port  70 . Port  70  is in fluid communication with the outlet port  38  via chamber  46 , and thus the exhaust gas  98  from the passageway  86  flows through the outlet port  38  and to the intake manifold. The valve member  90  prevents fluid communication between port  70  and ports  30 ,  62 ,  66 . 
     The bypass mode of operation of the EGR system  24 , as shown in  FIG. 2 , may be used, for example, during a cold start of the engine  14 , when exhaust gas cooling is not necessary and when exhaust gas pressure is low. The dual pass mode of operation may be used, for example, when a high differential pressure is present between the exhaust manifold and the intake manifold. The dual pass mode of operation has increased flow resistance than the single pass mode, but is characterized by a high degree of cooling because the effective flow length of the exhaust gas in the heat exchanger  50  is larger in the dual pass mode than in the single pass mode. Assuming, for example, that the first and second passageways  54 ,  58  are of equal length, then the exhaust gas flows twice the distance through the heat exchanger  50  in the dual pass mode than in the single pass mode. 
     The single pass mode may be used, for example, when EGR cooling is desired but there is a relatively low pressure differential between the exhaust manifold and the intake manifold. The effective flow length of the exhaust gas through the heat exchanger  50  in the single pass mode is approximately half the effective flow length of the exhaust gas in the dual pass mode (assuming passageways  54 ,  58  have identical lengths). However, the exhaust gas is distributed between the two passageways  54 ,  58 , and therefore is distributed across a greater cross sectional area than in the dual pass mode. The shorter effective flow length and the larger flow area provide reduced flow resistance than in the dual pass mode. The slower velocity of the exhaust gas in the single pass mode compared to the dual pass mode permits effective EGR cooling in the heat exchanger  50 . 
     It should be noted that other valve configurations may be employed within the scope of the claimed invention to achieve the three modes of operation described herein. For example, in an alternative embodiment, and within the scope of the claimed invention, the valve housing may be such that the ports are aligned linearly, and a slide valve (not shown) is selectively movable to control the flow between the ports to achieve the three modes of operation. In another alternative embodiment, and within the scope of the claimed invention, more than one valve member may be employed to control the flow of exhaust gas between the ports. 
     Those skilled in the art will recognize that another valve (not shown) may be employed within the EGR system  24  to regulate the amount of exhaust gas diverted from the exhaust manifold to the intake manifold within the scope of the claimed invention. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.