Patent GB-962905-A (GB)
Title: Improvements in or relating to variable pitch propellers
Inventor: ELMES ROBERT TERENCE
IPC: B63H3/08
Filed: 1959-10-16
Abstract: 962,905. Variable pitch propellers. DOWTY ROTOL Ltd. Oct. 13, 1960 [Oct. 16, 1959] No. 35168/59. Heading B7V. The stops of a variable pitch propeller are withdrawn successively by varying the pressure in a third hydraulic conduit additional to those which supply liquid to the opposite ends of the pitch control motor. The motor 17, 18 is connected with the blades 13 through a crankpin 15 and rod 16 and the pitch adjustment is controlled by a constant speed unit 20 associated with a pump 23 which delivers pressure liquid through the valve 22 to the motor 17, 18 via conduits 25, 27 or 26, 28 to respectively move the blades to coarser or finer pitch. The stops 30 arranged in a ring are mounted each upon one end of a resilient finger 31 and are prevented from moving endwardly by a retaining member 32 and are provided to limit movement of the ram 17 in the direction of finer pitch. The member 32 is slidably mounted upon a core 33 and has a stepped outer periphery 32b, 32c and 32d which steps upon axial movement of the member 32 cause the stops 30 to move radially out and so limit the movement of the ram 17 by abutting one of the shoulders 36a, 36b or 36c. A solenoid-operated valve 95 receives pressure liquid, through a conduit 96, from the pump 23 and by-pass valve 97 and when opened passes liquid to the underside of the piston 99 through unit 97 and conduit 98 to gag the relief valve 101 of the fine pitch conduit 26 to increase the operating pressure in that circuit. This higher pressure is transmitted through the passageway 57 to the chamber 56, movement of the ram 17 being limited by the stop 30 abutting shoulder 36a. The increased pressure in chamber 56 displaces the valve 48 against the spring 49 to open passageway 51 and allow the pressure to pass to the chambers 45e, 45b to move the jack pistons 43, 44 forward which movement brings the step 32c radially within the ring of stops 30 allowing the ram 17 to slide over until the shoulder 36b abuts the stops. At this time pressure liquid in conduit 98 is transmitted through conduit 102 to the solenoid-operated valve 90 and as soon as this is opened liquid passes through the conduit 91 to open valve 88 and permit pressure to enter the said third oil line 87 from conduit 89. Liquid under pressure is then conveyed through the duct 60 into the bore 61 to act on the land 65 of the valve spool 62 to displace the valve against the effort of the spring 66 and open the passageway 71 to the pressure liquid which passes to the chamber 74a via chamber 72 and ports 73 to move the jack piston 40. This movement causes the shoulder 39a to engage behind the flange 32e to displace the ring 32 to bring the step 32d radially within the stops 30 and thereby free the ram 17 for further sliding movement which is limited by the shoulder 36c abutting the stops 30. This position of the ram corresponds to a propeller pitch of zero, rearward movement of the ram to coarsen the propeller pitch frees the stops 30 and allows the spring 34 to move the ring 32 to reset the stops. In order to allow the propeller to move into the reverse pitch range the solenoids of valves 95, 90 are energized, to effect hydraulic supply to the valve 90 to open valve 93 to allow pressure liquid to pass to the conduit 87, together with that of the valve 105 to effect displacement of the piston 104, through conduit 107, to gag the relief valve 103 and increase the operating pressure in the conduit 87. The pressure in the third conduit 87 is conveyed through a duct 60 into the bore 61 to displace the spool 62 so that the land 65 opens the passageway 71 to move the piston 40 until the passageway 71 is closed by the stop at the rearward end of the chamber 72 causing a pressure build-up in the conduit 87 which is limited by the gagged blow of relief valve 103. The increased operating pressure of the end of the bore 61 displaces the spool 62, spring 66 and stop member 67 forward against the effort of the coil spring 68 until the land 64 opens the passageway 76 to move the piston 40 rapidly forward which moves the ring 32 further forward to bring the step 32a clear of the stops 30 thereby freeing the ram 17 for forward movement to adjust the propeller to reverse pitch range, the movement being stopped when the ram abutment 17a comes against the stop 18a. The pressure in the third oil line 87 may be increased any number of times to remove a similar number of stops either by separate solenoids controlling a relief valve capable of being gagged the desired number of times or alternatively by a number of different relief valves having different settings each being controlled by a solenoid. The jack piston 40 may be provided with a stepped movement by a valve arranged within it which is positioned by a pressure modulating device under the control of an electromagnetic device. Specifications 790,226, 818,611, 818,612, 818,701 and 818,702 are referred to.