Patent ID: 7152671

Claim:
An exhaust gas heat exchanger having a plurality of tubes which are stacked in such a manner as to become parallel with each other and through which exhaust gases from an internal combustion engine pass, a tank in which said plurality of tubes are accommodated, a coolant passage formed in the interior of said tank and constructed to allow coolant to flow around said plurality of tubes, bonnets coupled to ends of said plurality of tubes for distributing exhaust gases to said plurality of tubes or collecting exhaust gases that have passed through said plurality of tubes and core plates having openings through which the ends of said plurality of tubes are passed, respectively, and adapted to constitute partitions between said bonnets and said coolant passage and being brazed, said exhaust gas heat exchanger being characterized in that; said tubes each comprise: a first channel-shaped plate having a bottom wall and two planar transverse side edges extending generally perpendicular to the bottom wall of the first channel-shaped plate; a second channel-shaped plate having a bottom wall and two transverse side edges extending generally perpendicular to the bottom wall of the second channel-shaped plate and interfitting closely within the planar transverse side edges of the first channel-shaped plate to form a generally rectangular enclosure, and inner fins disposed between said first plate and said second plate, a planar stepped portion formed generally perpendicular to the bottom wall of the second channel-shaped plate on each of said transverse side edges of said second channel-shaped plate on which said first plate is fitted, said planar stepped portion having a height substantially equal to the thickness of said planar transverse side edges of said first plate, and protruding inwardly of said tube.