Patent ID: 8545357

Claim:
A gear transmission comprising: an internal gear; an external gear having a number of teeth differing from a number of teeth of the internal gear, being configured to revolve orbitally around a first axis line of the internal gear in a meshing state with the internal gear, and having a center through hole at its center and an offset through hole at a position offset from its center; a carrier having a column-shaped member and a pair of supporting members, wherein the column-shaped member passes through the offset through hole of the external gear, and each one of the pair of supporting members supports a respective end of the column-shaped member and is supported by the internal gear in a state allowing the pair of supporting members to rotate around the first axis line of the internal gear; a crank member having a shaft and an eccentric rotation member, wherein the shaft passes through the center through hole of the external gear and a pair of first grooves is formed on the surface of the shaft at positions between which the eccentric rotation member is interleaved, and the eccentric rotation member has a second axis line of rotation at a position offset from a third axis line of the shaft and is fixed in the center through hole of the external gear; and first rolling elements and first outer races arranged between the supporting members of the carrier and the first grooves of the crank member, wherein the first axis line and the third axis line are coaxial, each first groove has a first edge and a second edge, the first edge of a respective one of the first grooves is positioned on an outer side of the shaft relative to the second edge of the respective one of the first grooves in a direction along the second axis line, a first diameter of the shaft at a position where the first edge of the respective one of the first grooves is formed is smaller than a second diameter of the shaft at a position where the second edge of the respective one of the first grooves is formed, and the shaft of the crank member is supported such that the shaft is configured to rotate with respect to the carrier and its movement in an axial direction of the carrier is restricted, and wherein radially inward portions of each of the first rolling elements directly contact each of the first grooves, respectively, and radially outward portions of each of the first rolling elements interact with each of the first outer races, respectively.