Variable pitch mechanism for fan blades

A pitch varying mechanism for a variable pitch fan in which a plurality of fan blades are supported in a rotor for rotative movement about their longitudinal axes and in which a drive shaft is provided for rotatively driving the rotor so that the fan blades are carried in a rotative path, the mechanism comprises, in combination:

• a. gear train means for providing output rotation in two directions;
• b. bi-directional clutch means rotatively connected to the drive shaft, a fixed structure and the gear train to provide the latter with rotational output alternately in one direction and the other;
• c. energizing means for selectively actuating the bi-directional clutch means to effect output rotation of the gear train means in a predetermined direction;
• d. a cageless planetary gear train comprising a plurality of ring gears meshing with a plurality of planets arranged concentrically of the drive shaft axis and radially outwardly of the bi-directional clutch means and the gear train means and connected to each of the fan blades to rotate the latter and change their pitch;
• and
• e. a bi-directional, no-back, clutch-brake connected to the gear train to transmit output rotation of the gear train means to the cageless planetary gear train to effect pitch-change of the fan blades and prevent transmission of the torque load on the fan blades to the gear train means during steady state operation when no blade pitch-change is being effected.