Gear drive for gas turbine engine

A multiple gas turbine engine drive system having first and second core engines with a power turbine output shaft connected to drive a fan and including a load sharing cross-over drive between each of the engine output shafts to maintain power transfer to each of the fans when one of the engines is disconnected from the system, an overrunning clutch assembly which responds to a negative torque produced by a freewheeling fan,

• a right angle gear box assembly connecting each of the output shafts to the cross-over drive, each gear box assembly having an input gear connected to one of the power turbine output shafts and to the fan and further having an output gear connected to the cross-over drive, bearing means to support said input and output gears for limited axial movement, said input gear and said output gear defining a first torque loop and having meshed gear teeth thereon with a tooth geometry to produce an outboard thrust on said input gear during normal drive between the input and output gears, means for limiting outboard axial movement of said input gear in response to the output thrust imposed thereon during power transfer from the engine to the gear box assembly, the fan and the cross-over drive, idler gears in said gear box each having gear teeth thereon in meshed engagement with said gear teeth on said input and output gears respectively, to define a second torque loop to split torque transfer from each of the output shafts to each cross-over drive during transfer of torque from the input gear to the output gear in response to normal engine operation, each of said right angle gear box assemblies having a reverse torque imposed thereon when the engine connected thereto is disconnected from the system wherein power is transferred from a cross-over drive to an output gear to drive it in a reverse direction and to impose a reverse torque and drive on the input gear, said input and output gear teeth geometry including means responsive to the reversal of torque through said gear box assembly to produce a reverse thrust on the input gear to shift it inboard of the gear box assembly to maintain a continued drive mesh between the input, output and idler gears to maintain a reverse load carrying gear path from the output gear to the input gear and a reverse load carrying path from the output gear through the idler gears thence to the input gear whereby load sharing is maintained in both directions of torque transfer through the gear box assembly thereby to enable use of reduced weight component parts in the gear box assembly to transfer power from each of the engines to their respective output shafts and fans during both normal engine operation and disconnected engine operation wherein power is transferred to both of the engine loads from one of the engines.