Swing internal contact type planetary gear device and rotation drive device

A swing internal contact type planetary gear device comprising:

• an eccentric body rotating about an input/output axial line and having a center line being an eccentric axial line, the eccentric axial line is deviated from the input/output axial line;
• an internally toothed gear wheel provided with an annular internal tooth body and a plurality of internal teeth formed integrally with the internal tooth body in an inner circumferential side thereof, the center line thereof being the input/output axial line;
• and
• an externally toothed gear wheel provided with an annular external tooth body and a plurality of external teeth formed integrally with the external tooth body in an outer circumferential side thereof, the externally toothed gear wheel being relatively rotatably supported on the eccentric body and swingably rotating relative to the internally toothed gear wheel in meshing engagement therewith under the driving condition, the center line thereof being the eccentric axial line, wherein,
• each of the internal and external teeth is provided with an involute tooth profile and under the driving condition;
• one of the internal tooth body and the external tooth body elastically deforms in an extending direction in a circumferential direction and the other of the internal tooth body and the external tooth body elastically deforms in a contracting direction in a circumferential direction, whereby the number of meshing teeth between the internal tooth and the external tooth is set to be larger than the number of meshing teeth between the internal tooth and the external tooth under a non-driving condition;
• assuming that a tooth number “i” of each of reference meshing teeth of with the internal tooth and the external tooth meshing with each other under a non-driving condition is defined as “1” and the number “i” of each of the internal tooth and the external tooth is defined to be the value added every one (1) whenever it is leaving away from the reference meshing tooth,
• a displacement amount in an extending direction of one of the teeth between the internal tooth and the external tooth, each tooth being numbered as “i”, is defined to be the value of δ1,i,
• a displacement amount in a contracting direction of the other of the teeth between the internal tooth and the external tooth, each tooth being numbered as “i”, is defined to be the value of δ2,i, and that,
• a gap between the tooth flank of the internal tooth and the tooth tip of the external tooth each tooth being numbered as “i”, is defined to be the value of δi, wherein, a module of each of the internally toothed gear wheel and the externally toothed gear wheel is set as the value satisfied the following formula (1):
• [M1] |δ1,i+δ2,i|=δi (1).