Differential gear box

Claim 1

Apparatus for controlling pitch variations of the blades of a propeller, comprising: a first planetary gearset including a sun gear, a ring gear and at least one planetary gear meshed with the sun and ring gears, the sun gear being statically grounded; a second planetary gearset stacked in concentric juxtaposition with the first planetary gearset and including a sun gear, a ring gear and at least one planetary gear meshed with the sun and ring gears, the planetary gear being coupled for conjoint orbiting with the planetary gear of the first gearset; main rotor drive input means including cylindrical input shaft means spaced entirely above and being of and concentric with the planetary gearsets, the input shaft means being meshed on the interior thereof with the ring gear of the second planetary gearset, and rotor drive gear means meshed with gear means on the outside of the cylindrical input shaft means; blade actuator output means located entirely above the planetary gearsets and including output shaft means concentric with the planetary gearsets, the output shaft means being disposed within the cylindrical input shaft means and coupled to the ring gear of the first planetary gearset to be rotated thereby; and selectively operable differential drive input means located entirely below the planetary gearsets and coupled to the sun gear of the second planetary gearset, whereby inoperation of the differential drive input means effectively grounds the sun gear and permits the main rotor drive input means and the blade actuator output means to rotate at the same speed, and selective operation of the differential drive input means to rotate the sun gear of the second planetary gearset effects a differential speed between the rotor drive input means and the blade actuator output means.