Patent ID: 8079409

Claim:
An exhaust gas recirculation (EGR) cooler, comprising: a plurality of tubes; and a shell which encloses said tubes, cooling water being supplied to and discharged from said shell during use of the EGR, exhaust gas being guided from a diesel engine into said tubes to be heat exchanged with said cooling water during use of the EGR, wherein an inner periphery of each of said tubes is formed with three streaks of spiral protrusions running without crossing and with phases peripherally shifted or displaced with each other, a pitch ratio of each of said spiral protrusions to an inner diameter of each of said tubes being 2.0-4.0, a ridge height ratio of each of said spiral protrusions to said inner diameter of each of said tubes being 0.1-0.2, and wherein a pitch of a respective one of the spiral protrusions is an axial length between neighboring points within the same phase on the respective one of the spiral protrusions, and the inner diameter of each of the tubes is an internal diameter of the tubes measured at a point within the tubes that does not include any spiral protrusions.