| 摘要 |
PROBLEM TO BE SOLVED: To improve reliability of parts, reduce a manufacturing cost, and improve thermal efficiency ratio in an EGR gas cooling device. SOLUTION: Gas discharged from an exhaust system of an internal combustion engine is partially returned to an intake system through an EGR pipe 2, and added to air-fuel mixture as EGR gas G. In such reciruclation, an EGR gas cooling device which cools the EGR gas G has a double pipe structure provided with a cooling pipe 3 for flowing cooling water W so as to cool the EGR gas G. An inner pipe (the EGR pipe 2 or the cooling pipe 3) composing the double pipe structure has a recession 21 prepared by recessing a part of a pipe wall inward.
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