Patent ID: 8004144

Claim:
A rotor for an automotive alternator, comprising: a rotary shaft; a pair of first and second magnetic pole cores each of which includes a hollow cylindrical boss portion, a disc portion, and a plurality of magnetic pole claws, the boss portion being fit on the rotary shaft to rotate along with the rotary shaft, the disc portion extending radially outward from an axially outer part of the boss portion, each of the magnetic pole claws axially extending from a radially outer part of the disc portion, the magnetic pole claws of the first magnetic pole core being interleaved with the magnetic pole claws of the second magnetic pole core; a bobbin fit on both the boss portions of the first and second magnetic pole cores; a field coil wound around the bobbin; a plurality of permanent magnets each of which is interposed between adjacent two of the magnetic pole claws of the first and second magnetic pole cores in a circumferential direction of the rotary shaft, so as to reduce magnetic flux leakage between the two magnetic pole claws; and a positioning mechanism made up of at least one of the rotary shaft, the first and second magnetic pole cores, and the bobbin, the positioning mechanism functioning to position the first and second magnetic pole cores in the circumferential direction of the rotary shaft with intervals between adjacent pairs of the magnetic pole claws of the first and second magnetic pole cores being even, wherein both the boss portions of the first and second magnetic pole cores are integrated into a common boss portion to the first and second magnetic pole cores, the common boss portion has two first engaging portions that are respectively provided on both axial end faces of the common boss portion, each of the disc portions of the first and second magnetic pole cores has a second engaging portion that is provided on an axial end face of the disc portion to engage with a corresponding one of the first engaging portions of the common boss portion, the first engaging portions of the common boss portion and the second engaging portions of the disc portions of the first and second magnetic pole cores together make up the positioning mechanism, and for each engaging pair of the first engaging portions of the common boss portion and the second engaging portions of the disc portions, one of the first and second engaging portions is a protrusion from its respective axial end face and the other is a recess within its respective end face.