| 摘要 |
An automatic speed reducing ratio-switching apparatus is provided to automatically switch a speed-reducing ratio to be transmitted from an output shaft connected to a carrier to a displacement member of an actuator. A planetary gear mechanism(214) has an input shaft(226), an output shaft(228), a sun gear(216), planet gears(218a to 218c), and an internal gear(220). A viscous resistance member is installed in an inner portion of a carrier inserted into the internal gear, the planet gears, and the internal gear. The viscous resistance member generates a thrust force between the internal gear and the planet gears. A brake mechanism causes the internal gear to be displaced in parallel by using the thrust force in a direction toward the input shaft or a direction toward the output shaft. A helix angle of each helical gear is in a range from 25 degrees to 45 degrees.
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