Planetary roller driving device and steering apparatus comprising the same

A planetary roller driving device comprising:

• a planetary roller speed up gear having a first carrier being a first input axis and a first sun roller being a first output axis;
• a planetary roller reduction gear having a second sun roller being a second input axis and a second carrier being a second output axis, the second input axis being joined with the first output axis;
• a roller ring driving mechanism which drives one of a first roller ring of the planetary roller speed up gear and a second roller ring of the planetary roller reduction gear;
• a roller ring rotation control circuit which controls a rotation of the roller ring driving mechanism corresponding to an external environmental condition;
• a torque-assisting mechanism which provides an assisting torque to the first input axis or the second output axis;
• and
• a singular housing which unitarily accommodates the planetary roller speed up gear, the planetary roller reduction gear, the roller ring driving mechanism, and the torque-assisting mechanism,
• wherein the torque-assisting mechanism includes:
• a motor-directly-connected reduction gear which is directly connectable to a motor, wherein the motor-directly-connected reduction gear is a worm reduction gear having a worm lead angle which prevents locking thereof even when a power is transmitted from a worm wheel to a worm axis, wherein
• the torque-assisting mechanism further includes an assisting-torque control circuit which controls an output of the motor, and thereby controlling said assisting torque corresponding to the external environmental condition, and
• wherein the planetary roller driving device further comprises an encoder which is directly connected to the worm reduction gear along the worm axis and measures a rotational angle of the worm reduction gear about the worm axis.