Gear housing for a planetary gear device that structurally isolates an inner gear

An apparatus for suppressing noise produced in a planetary gear device, comprising:

• an inner gear with a first contacting portion formed on an end face of the inner gear on a first side of the inner gear in an axial direction;
• and
• a housing for containing the inner gear as a floating inner gear with a second contacting portion for limiting movement of the inner gear through contact with the first contacting portion such that a gap is formed between an inner peripheral surface of the housing and the inner gear,
• wherein one of the first contacting portion and the second contacting portion comprises a plurality of raised protrusions formed in pairs with a space therebetween and spaced around a circumference direction, and
• wherein the other of the first contacting portion and the second comprises a plurality of raised protrusions that are formed so as to be inserted between the raised portions that are formed in a pair, and are disposed spaced around the circumference direction.