Abstract: 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.

Abstract: In a resin backlashless gear 1, the radial outer portions 7, 8 of first and second gear portions 3, 4 are connected to a radial inner portion 2 by means of radial ribs 10, 11 so as to be capable of being displaced in rotational directions. The elastic deformation of the radial ribs 10, 11 decreases the dislocation of the teeth 5, 6 of the first and second gear portions 3, 4 in pitch circle directions so that the dislocation is equal to backlash to cause the teeth 5, 6 of the first and second gear portions 3, 4 to elastically contact the teeth of a companion gear meshing with the resin gear to absorb the backlash.

Abstract: 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.