GB1195963A - Gear Transmission for Driving Variable Pitch Aerofoil Blades. - Google Patents

Abstract

1,195,963. Jet propulsion plant; axial flow fans. ROLLS-ROYCE Ltd. Feb. 22, 1968 [Dec. 5, 1966], No. 48909/67. Divided out of 1, 195, 961. Headings F1C and F1J. Variable pitch aerofoil blades have an adjusting mechanism comprising radial shafts extending through an inner set of radially extending blades and drivingly connected to one or more peripheral shafts which engage the roots of the variable pitch blades by a worm and wheel drive. The Specification describes in greater detail the transmission arrangement for the pitch adjusting mechanism of the gas turbine engine ducted fan blades described in Specification 1, 195, 961. The fan assembly comprises outer variable pitch blade parts 2 and inner non-adjustable blade parts 1, the parts being connected by a ring 15. Each blade part 2 is of metallic or plastics material and has a titanium internally ribbed root 4 threaded at one end so that a geared steel sleeve 8 can be screwed over the root 4. A flange 70 on the sleeve 8 carries a plain bearing 6b which retains the blade part 2 radially in position against the action of centrifugal and torsional forces whilst leaving the geared portion of the sleeve 8 substantially unaffected by such forces. The mating threads of the root 4 and sleeve 8 include a venier adjustment to permit setting of the desired preload of the bearing 6b prior to locking the sleeve to the root. Two double enveloping worms 9 engage diametrically opposite portions of the geared sleeve 8, only one worm 9a being shown. The worms 9 are connected by shafts 21a, 21b respectively to gear wheels 22a, 22b mating with a further worm 23 connected, in turn, to a shaft 24 passing through a blade part 1. The shaft 24 has a pinion (26), Fig. 2 (not shown) at its inner end which can be driven by an annular gear (30), as described in Specification 1, 195, 961. The connection between shaft 24 and worm 23 is by way of a spline and a flexible diaphragm 51 in order to isolate the worm 23 from radial movement of the shaft 24, the worm being mounted on bearing 53, 54 from the ring 15. The wheels 22a, 22b are mounted from ring 15 by taper bearings 57 and are splined at 58 to the shafts 21a, 21b to allow for expansion. The shafts 21 each include a soldered joint in the region of splines 58 which will shear in the event of overloading. At its opposite end each shaft 21 is splined at 59 within worm 9, the latter being supported from the ring 15 by bearing 60, 61. The shaft 21 continues from the worm 9 by way of a flexible coupling 65 having a spider 67 to the worm 9 of an adjacent blade part 2, the arrangement being such that each shaft 24 and worm 23 is connected to four blade parts 2, on either side of the worm 23.