Patent ID: 8771126

Claim:
A traction drive mechanism comprising a first planetary roller mechanism and a second planetary roller mechanism that are connected in series, the first planetary roller mechanism including a plurality of first planetary rollers rotatably supported by a first carrier, the first planetary rollers being held in contact between a first sun roller and a first ring roller, the second planetary roller mechanism including a plurality of second planetary rollers rotatably supported by a second carrier, and the second planetary rollers being held in contact between a second sun roller and a second ring roller, wherein N 1 =3, N 2 =3, 4, 5, or 6, and (ρ 1 +1)×(ρ 2 +1)≧24+16×2 0.5 in which N 1 is the number of the first planetary rollers, N 2 is the number of the second planetary rollers, ρ 1 is the ratio between the inner diameter of the first ring roller and the outer diameter of the first sun roller, and ρ 2 is the ratio between the inner diameter of the second ring roller and the outer diameter of the second sun roller, and provided that N 2 =3, ρ 1 ≧0.102×(ρ 1 +1)×(ρ 2 +1)+1.196, and ρ 1 ≦min[0.204×(ρ 1 +1)×(ρ 2 +1)+3.123, 7+4×3 0.5 ] when a value of a smaller one of (0.204×(ρ 1 +1)×(ρ 2 +1)+3.123) and (7+4×3 0.5 ) is min[0.204×(ρ 1 +1)×(ρ 2 +1)+3.123, 7+4×3 0.5 ], or provided that N 2 =4, ρ 1 ≧(2−2 0.5 )×(ρ 1 +1)×(ρ 2 +1)/4−1, and ρ 1 ≦min[0.185×(ρ 1 +1)×(ρ 2 +1)+1.320, 7+4×3 0.5 ] when a value of a smaller one of (0.185×(ρ 1 +1)×(ρ 2 +1)+1.320) and (7+4×3 0.5 ) is min[0.185×(ρ 1 +1)×(ρ 2 +1)+1.320, 7+4×3 0.5 ], or provided that N 2 =5, ρ 1 ≧0.206×(ρ 1 +1)×(ρ 2 +1)−1, and ρ 1 ≦min[0.234×(ρ 1 +1)×(ρ 2 +1)−0.480, 7+4×3 0.5 ] when a value of a smaller one of (0.234×(ρ 1 +1)×(ρ 2 +1)−0.480) and (7+4×3 0.5 ) is min[0.234×(ρ 1 +1)×(ρ 2 +1)−0.480, 7+4×3 0.5 ], or provided that N 2 =6, ρ 1 ≧0.25×(ρ 1 +1)×(ρ 2 +1)−1, and ρ 1 ≦min[0.278×(ρ 1 +1)×(ρ 2 +1)−0.603, 7+4×3 0.5 ] when a value of a smaller one of (0.278×(ρ 1 +1)×(ρ 2 +1)−0.603) and (7+4×3 0.5 ) is min[0.278×(ρ 1 +1)×(ρ 2 +1)−0.603, 7+4×3 0.5 ].