US Patent 7189062 Centrifugal impeller

A centrifugal impeller particularly for a turbo-charger includes a circular disc member, a boss portion formed at a central portion of the disc member and having a central through hole into which a rotational shaft is inserted, an impeller blade integrally formed on one surface side of the disc member, and a ring-shaped rib member arranged on the other surface side of the disc member so as to be coaxial with a center axis of the boss portion. A thickness reduced portion is formed to the disc member so as to have a thickness smaller than that of another portion of the disc member, and the thickness reduced portion is arranged adjacent to the rib member.