Exhaust gas heat exchanger

Abstract

A tube is constituted by a pair of plates which are fitted with each other in such a manner as to put an inner fin between the plates. Differences in level are formed between the two plates, which differences in level is compensated by either a tapered wall or a stepped wall, whereby the outer wall surface of the tube is made substantially level thereover. A gap which is formed between the outer wall surface of the tube and a core plate, when the tube is passed through the core plate, can be as small as possible whereby the brazing properties can be improved.

1 . An exhaust gas heat exchanger comprising: 
 a tank defining a tank passage;    a plurality of tubes disposed within the tank passage of the tank in such a manner as to be parallel with each other, each tube defining a tube passage;    bonnets coupled to ends of said plurality of tubes in communication with the tube passages;    core plates having openings through which ends of said plurality of tubes are passed, respectively, the core plates defining partitions between the tank passage and the tube passages;    said tubes each comprise:    a first plate having a bottom wall and two transverse side walls, each transverse side wall having a curved wall portion extending from the bottom wall;    a second plate having a bottom wall and two transverse side walls, each of the two transverse side walls of the second plate extending over a respective transverse side wall of the first plate, each of the two transverse side walls of the second plate having a curved wall conforming to the curved wall of the respective transverse side wall of the first plate.    
   
   
       2 . The exhaust gas heat exchanger according to  claim 1  further comprising an inner fin disposed with at least one of the tube passages.  
   
   
       3 . The exhaust gas heat exchanger according to  claim 1  wherein the curved walls of the second plate each define a tapered region, which reduces a thickness of the second plate.  
   
   
       4 . The exhaust gas heat exchanger according to  claim 3  further comprising an inner fin disposed with at least one of the tube passages.  
   
   
       5 . The exhaust gas heat exchanger according to  claim 1  further comprising a stepped portion formed on the first plate, the stepped portion having a height substantially equal to thickness of the second plate.  
   
   
       6 . The exhaust gas heat exchanger according to  claim 5  further comprising an inner fin disposed with at least one of the tube passages.  
   
   
       7 . An exhaust gas heat exchanger comprising: 
 a tank defining a tank passage;    a plurality of tubes disposed within the tank passage of the tank in such a manner as to be parallel with each other; each tube defining a tube passage;    bonnets coupled to ends of said plurality of tubes in communication with the tube passages;    core plates having openings through which ends of said plurality of tubes are passed, respectively, the core plates defining partitions between the tank passage and the tube passages;    said tubes each comprise:    a first plate having a first bottom wall and two side walls, each side wall of the first plate having a side portion extending transversely to the first bottom wall and a curved portion disposed between the side portion and the first bottom wall;    a second plate having a second bottom wall and two side walls, each side wall of the second plate having a side portion extending transversely to the second bottom wall, a curved portion disposed between the side portion and the second bottom wall and a formed portion extending from the side portion, the formed portion following the contour of the curved portion of the first plate.    
   
   
       8 . The exhaust gas heat exchanger according to  claim 7  further comprising an inner fin disposed with at least one of the tube passages.  
   
   
       9 . The exhaust gas heat exchanger according to  claim 7  wherein the formed portion of the second plate each define a tapered region, which reduces a thickness of the second plate.  
   
   
       10 . The exhaust gas heat exchanger according to  claim 9  further comprising an inner fin disposed with at least one of the tube passages.  
   
   
       11 . The exhaust gas heat exchanger according to  claim 7  further comprising a stepped portion formed on the first plate, the stepped portion having a height substantially equal to thickness of the second plate.  
   
   
       12 . The exhaust gas heat exchanger according to  claim 11  further comprising an inner fin disposed with at least one of the tube passages.