| 摘要 |
PROBLEM TO BE SOLVED: To improve the heat exchanging efficiency of an EGR cooler by forming spiral projections in plural rows on an inner peripheral surface of a tube, and to prevent an undesirable damage form such as the leakage of cooling water caused by the damage of a part penetrating and fixing both ends of the tube even if a part of the tube thermally expands and receives compressed stress due to an air reservoir. SOLUTION: This EGR cooler heat-exchanges between exhaust gas 10 and cooling water out of a tube 3 by letting the exhaust gas 10 pass through the tube 3. On at least a part of an inner peripheral surface in a longitudinal direction of the tube 3, spiral projections 11, 12 in plural rows are formed while shifting a phase in the longitudinal direction of the tube 3. The rest part of the tube 3 is left as a non-machined straight portion 13.
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