GB707814A - Improvements in or relating to thrust-transmitting mechanisms applicable e.g. to variable pitch propellers - Google Patents

Abstract

707,814. Fluid-pressure servomotor-control systems. ROTOL, Ltd. Oct. 31, 1951 [Nov. 15, 1950], No. 27987/50. Class 135. [Also in Group XXXIII] A thrust-transmitting mechanism comprises a piston and rod assembly and a co-acting cylinder with closed ends, the piston and rod assembly being axially displaceable with consequent movement of the cylinder in the same direction, the assembly and cylinder being arranged for rotation relatively to one another, and valve means actuated on axial movement of the assembly relatively to the cylinder to admit pressure fluid to the end of the cylinder which is reduced in volume by such movement to build up a pressure therein such that the thrust transmitted to the cylinder equals the thrust producing the movement of the assembly. As shown, the mechanism 19, Fig. 1, is incorporated in a variable-pitch, contra-rotating airscrew assembly comprising front blades 7 and rear blades 8. The pitch of blades 7 is adjusted through links 12 by a piston 11 supplied with oil under pressure through passages 14, 15 in the propeller shaft. The thrust of the piston is transmitted by rods 18 to the piston 22 of the mechanism and thence by the cylinder 24 to links 20 of the blades 8. Passages in the rods 18 connect the chambers 16, 17 on opposite sides of piston 11 with passages 28, 32, respectively in piston 22 leading to chambers 30, 34 on opposite sides of piston 22. Passages 28, 32, are controlled by piston valves 25, 26 respectively, slidable in the piston and abutting the end walls of the cylinder. Running clearances between the piston and the cylinder, due to the opposite rotations thereof permit a leak between chambers 30 and 34 and also from the chambers to the low pressure side of the oil source, e.g. via chambers 62 and ducts 63, 64. Thus, movement of piston 11, e.g. to the right due to oil supplied to chamber 16, causes movement of piston 22 to the right to decrease the volume of chamber 30 and opening of passage 28 to connect chambers 16 and 30, whereby the cylinder follows the piston until the piston stops. In another arrangement, a single piston valve may be used, and in yet another arrangement, passages 55, 56, Fig. 4, from chambers 17, 16 respectively terminate in annular grooves 53, 54 in the piston and co-act with grooves 57, 58 in the cylinder. Thus the piston acts as the control valve for chambers 30, 34.