Patent Publication Number: US-7707997-B2

Title: Cooling apparatus of exhaust gas recirculation system and method using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority to, and the benefit of, Korean Patent Application No. 10-2007-0055031, filed in the Korean Intellectual Property Office on Jun. 5, 2007, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   (a) Field of the Invention 
   The present invention relates to a cooling apparatus and method of an exhaust gas recirculation system. 
   (b) Description of the Related Art 
   Nitrogen oxides (NOx) are regulated pollutants. Exhaust gas recirculation (EGR) systems have recently been provided to address this. Generally, NOx is most prevalent when the air-fuel ratio is high. An exhaust gas recirculation system mixes some of the exhaust gas to the air-fuel mixture, reducing the amount of oxygen in the air-fuel mixture, and so lessening generation of NOx. 
   A hot-type EGR system retards ignition, lessens the air-fuel ratio, and lessens the amounts of particulate materials (PM) and hydrocarbons (HC), as well as the amount of NOx, while a cooled-type EGR system prevents combustion by cooling the exhaust gas and the combustion chamber. Recently, the hot EGR system and the cooled EGR system have been used together: the hot EGR system is used at low load and the cooled EGR system is used at high load. 
   Generally, temperature of exhaust gas is very high, and so a cooling apparatus is provided to the EGR system. The cooling apparatus should be made of a material that is durable at the high temperatures to which it is exposed. A typical material is stainless steel, which is very heavy and costly. 
   The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
   SUMMARY OF THE INVENTION 
   A cooling apparatus of an exhaust gas recirculation system includes a first cooling portion, made of a first material, that receives recirculation exhaust gas; and a second cooling portion, made of a second, different material, that receives the recirculation exhaust gas from the first cooling portion and exhausts the recirculation exhaust gas out of the apparatus. 
   The second material may have a heat-resistant temperature that is lower than that of the first material. The second material may be less dense than the first material. 
   The first material may be stainless steel and the second material may be aluminum. 
   The recirculation exhaust gas may flow in opposite directions within the first and second cooling portions. 
   The first cooling portion may have a first coolant passage, and the second cooling portion may have a second coolant passage. 
   Coolant may flow from the second coolant passage to the first coolant passage. 
   A gasket may be provided between the first cooling portion and the second cooling portion. 
   The gasket may be made of material that includes mica. 
   The gasket may be about 1.5-2.0 mm thick. 
   The first cooling portion may include a first cooling fin unit, and the second cooling portion may include a second fin unit. 
   The second cooling fin unit may be made of aluminum. 
   The second cooling fin unit may be about 2.5 mm thick or thicker. 
   At least one mounting bracket may be provided for mounting the apparatus to a cylinder head. 
   An elastic member may be provided between the mounting bracket and the cylinder head. 
   A cooling method of an exhaust gas recirculation system includes receiving a recirculation exhaust gas in a first cooling portion made of a first material; cooling the recirculation exhaust gas in the first coolant portion; receiving the recirculation exhaust gas in a second cooling portion made of a second, different material; and cooling the recirculation exhaust gas in the second coolant portion. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a cooling apparatus of an exhaust gas recirculation system according to an exemplary embodiment of the present invention, with a cylinder head shown schematically. 
       FIG. 2  is an exploded perspective view of the apparatus of  FIG. 1 . 
       FIG. 3  is a cross-sectional view along the line I-I of  FIG. 2 . 
       FIG. 4  is a perspective view of a first coolant passage and a first cooling fin of the apparatus of  FIG. 1 . 
       FIG. 5  is a perspective view of a second coolant passage and a second cooling fin unit of the apparatus of  FIG. 1 . 
   

   DESCRIPTION OF REFERENCE NUMERALS INDICATING PRIMARY ELEMENTS IN THE DRAWINGS 
   
     
       
         
             
             
           
             
                 
             
           
          
             
               100: 
               first cooling portion 
             
             
               110: 
               first coolant passage 
             
             
               120: 
               first cooling un unit 
             
             
               130: 
               coolant outlet 
             
             
               200: 
               second cooling portion 
             
             
               210: 
               second coolant passage 
             
             
               220: 
               second cooling fin unit 
             
             
               230: 
               coolant inlet 
             
             
               300: 
               gasket 
             
             
               400: 
               mounting bracket 
             
             
               410: 
               elastic member 
             
             
               500: 
               cylinder head 
             
             
                 
             
          
         
       
     
   
   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
   As shown  FIG. 1 , a cooling apparatus of an exhaust gas recirculation system according to an exemplary embodiment of the present invention includes a first cooling portion  100  that is made of a first material. The first cooling portion  100  receives recirculation exhaust gas at the bottom right of  FIG. 1 . The apparatus also includes a second cooling portion  200  that is made of a second material and exhausts the recirculation exhaust gas received from the first cooling portion  100 . 
   The first cooling portion  100  and the second cooling portion  200  are manufactured independently from different materials, and are then connected to each other. 
   The second material may have a lower heat-resistant temperature, and be less dense, than the first material. 
   Recirculation exhaust gas is typically about 500-600° C., and thus, thermal insulation of the cooling apparatus must be excellent. In addition, because the cooling apparatus is cooled by engine coolant, resistance to corrosion must be excellent. As mentioned in the background section, stainless steel is typically used, but it is heavy and expensive. 
   The recirculation exhaust gas is cooled from about 500-600° C. to 120-150° C. during its journey through the cooling apparatus. 
   Therefore, in some embodiments, the first cooling portion is made of stainless steel and the second cooling portion is made of aluminum. The lower temperature EGR gas that has already been cooled in the first cooling portion is further cooling in the second cooling portion. Because of the lower temperature of the EGR gas at this point, aluminum has sufficient thermal characteristics to be used for the second cooling portion. Aluminum is also light and cheap. 
   As shown in  FIG. 1 , the flow path of the coolant and recirculation exhaust gas may be U-shaped. This shape provides good cooling efficiency and takes up a small volume. 
   Thus, the recirculation exhaust gas flows in opposite directions within the first cooling portion  100  and the second cooling portion  200 . 
   The first and second cooling portions  100  and  200 , as shown in  FIG. 4  and  FIG. 5 , include a first coolant passage  110  and a second coolant passage  210 , respectively, through which coolant flows. The coolant flows from the second coolant passage  210  to the first coolant passage  110 . 
   The first cooling portion  100  and the second cooling portion  200  also include a first cooling fin unit  120  and a second cooling fin unit  220 , respectively, to cool the recirculation exhaust gas by flowing of the coolant. 
   To provide enough thermal insulation, the second cooling fin unit  220  has a thickness to &gt;≈2.5 mm. 
   The second cooling fin unit  220  can be manufactured through a die casting process. 
   As shown in  FIG. 2 , the first and second cooling portions  100  and  200  are made of different materials, and so welding is not easily used to combine the two portions. Thus, a gasket  300  is disposed between the first cooling portion  100  and the second cooling portion  200 . 
   Because the thermal characteristics of the first and second cooling portions  100  and  200  are different, the gasket  300  is made of a durable material including mica. A thickness of the gasket is 1.5-2.0 mm for improving durability due to thermal expansion. 
   Mounting brackets  400  are mounted mount the cooling apparatus to a cylinder head  500 , as shown in  FIG. 3 . An elastic member  410  is disposed between each mounting bracket  400  and the cylinder head  500  in order to prevent transference of vibrations. 
   A cooling method of exhaust gas recirculation according to an exemplary embodiment of the present invention includes a first cooling step in which a recirculation exhaust gas flows into a first cooling portion  100  made of a first material, where the recirculation exhaust gas is cooled by coolant flowing through a first coolant passage  110  in the first cooling portion  100 , and a second cooling step in which the recirculation exhaust gas flows from the first cooling portion  100  into a second cooling portion  200  made of a second material that is different from the first material where the recirculation exhaust gas is cooled by coolant flowing through a second coolant passage  210  in the second cooling portion  200 . 
   While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.