A yaw drive method of a wind power generation apparatus, in which a second gear engaged with a first gear attached to one of tower or a wind power generation unit supported to the upper end of the tower so as to be capable of yawing and supported to a tower or to the upper end of the tower is rotated...http://www.google.ca/patents/US8022564?utm_source=gb-gplus-sharePatent US8022564 - Speed reducer for use in yaw drive apparatus for wind power generation apparatus, and yaw drive method and apparatus for wind power generation apparatus using the speed reducer
