| 摘要 |
1521545 Axial flow fans UNITED TECHNOLOGIES CORP 8 Oct 1975 [9 Oct 1974] 41224/75 Headings F1C and F1J [Also in Division F2] A ring 60 is rotatable on the hub 26 of a ducted thrust fan to vary the pitch of fan blades 24 via horns 50 bearing parallel sided slots 52 which engage rollers 62 on the ring. The horns are oriented each relative to its respective blade so that they are all parallel to the hub axis 20 when the blades are in the feathered pitch position. To maintain contact between the horn slots and rollers 62 over the full range of pitch change operation, the horns may be slightly curved, alternatively the slots may be open at the top and the rollers of a length sufficient to prevent them from becoming disengaged. The axis of each roller 62 extends through the point of intersection of the blade axes 34 and hub axis 20. Rotation of ring 60 relative to hub 26 is effected by a harmonic drive 70 driven via a differential gear mechanism 72, gear 78, one way clutch 76 and input shaft 74 connected to a servomotor. The harmonic drive comprises a non circular wave generator 88 which forces a flexible gear 92 into engagement at two or more points with internal splines on a flange 42 connected to hub 26. Flange 42 and gear 92 which is connected to ring 60 have differing numbers of teeth so that rotation of wave generator 88 causes shifting of the flange 42 relative to gear 92 resulting in rotation of ring 60 relative to hub 26. The rotating hub carries with it planet gears 84, 98 of differential 72, the harmonic drive 70 and sleeves 86, 94, and 100, whilst the clutch 76, sleeve 80 and gear 104 into which gears 84 mesh remain stationary. When pitch change is required, gear 78 rotates sleeve 80, the rotation being transmitted via planet gears 84 to sleeve 86 and wave generator 88 causing rotation of ring 60 relative to hub 26. |
