Planetary gear having its orbital gears out of phase

Claim 1

A planetary gear apparatus comprising: (a) a casing; (b) a first shaft rotatably supported by said casing; (c) a second shaft rotatably supported by said casing; (d) a sun gear fixed to said first shaft; (e) a fixed internal gear: (i) arranged concentrically with said sun gear and (ii) located in said casing; (f) a rotary internal gear: (i) arranged coaxially with said fixed internal gear, (ii) having a difference M in number of teeth with respect to the number of teeth of said fixed internal gear, (iii) coupled to said second shaft, and (iv) having an addendum circle the diameter of which is the same as the diameter of the addendum circle of said fixed internal gear; and (g) N (M≠N, N≠1) planet gears: (i) each of which revolves around said sun gear while revolving around its own axis, (ii) disposed at equal intervals circumferentially around said sun gear, (iii) each having a first gear portion meshed with said fixed internal gear and a second gear portion meshed with said rotary internal gear, the first gear portion of each one of said planet gears having the same number of teeth and the same addendum circle diameter as the second gear portion, (iv) either one of the first and second gear portions of said planet gears being meshed with said sun gear, and (v) when the number of said planet gears is designated by i=1, 2, . . . , N circumferentially, the phase of the teeth of the first gear portion of the i-th planet gear being shifted in the period of {(i-1)M}/N with respect to that of the teeth of the second gear portion.