Patent ID: 8714245

Claim:
A high torque planetary gear box assembly for a bottom hole assembly (BHA) used in drilling, the gear box assembly comprising: a housing having at least one stage with a plurality of levels; a sun wheel for connecting to an input shaft and having a gear portion within each level; at least one planet wheel coupled to the respective gear portion in each level; and a common carrier connected to the at least one planet wheel in each level, wherein the common carrier twists by an angle α as a result of torque applied thereto and the gear box assembly has a transmission ratio i such that a twisting angle β of the sun wheel is characterized by β=i*α, and a torsional rigidity of the sun wheel is about i 2 times less than a torsional rigidity of the common carrier to accomplish balanced engagement in all levels of the gear box assembly; wherein during operation, an external torque is transmitted by the sun wheel through the plurality of levels whereby tangential forces are transmitted from the gear portions to the respective at least one planet wheel, and, in turn, from the at least one planet wheel to the common carrier, and the sun wheel is designed to match torsional rigidity characteristics of the common carrier to substantially balance the tangential forces on each level.