Patent GB-818702-A (GB)
Title: Improvements in or relating to hydraulic variable pitch propellers
Inventor: CHILMAN JOHN ALFRED
IPC: B64C11/38
Filed: 1957-07-19
Abstract: 818,702. Variable pitch propellers. ROTOL Ltd. July 19, 1957, No. 22980/57. Class 114. The invention relates to a variable pitch propeller having an hydraulic pitch change motor, a flight cruise stop and a flight fine pitch stop with or without a third stop for zero pitch, there being hydraulic means for withdrawing the stops, the first using increased pressure in the pitch fining line and the other or others the " third oil line," for example as described in Specification 818,612. According to the invention an hydraulic pump supplies pressure fluid to a piston and cylinder assembly which loads the relief valve in the pitch fining circuit when a first electro-hydraulic valve is actuated and to an hydraulic relay to bring in the third oil line when a second electro-hydraulic valve is actuated. An hydraulic pump 86 feeds fluid constantly to a space 91 between lands 69, 70 on a spool valve 68 in a constant speed device 67, the upper end of the valve being connected through a lost motion device 319 with the stem 332 of a piston 318 working in a cylinder 329. Fine and coarse pitch lines 48<SP>1</SP>, 501 are opened selectively to the space 91 by downward and upward movements of the valve. A relief valve 115 disposed across the fine and coarse pitch conduits limits the pressure in the former ; the pressure is increased to withdraw the cruise stop by loading the valve through a spring 162 by a piston 114 to the rear of which pressure fluid is applied through a conduit 112 when the solenoid 101a of an electro-hydraulic valve 101 is actuated to open a valve 153 therein and close a valve 155 leading to a drain conduit 119, the conduit 112 leading into an annular space 111 between lands 107, 106 on a manually operated slide valve 182 and thence through a conduit 110 to the valve chamber 154 of the electro-hydraulic valve 101. The valve chamber 154 opens through a conduit 116 on to the inlet valve 167 of a second similar electro-hydraulic valve 117 controlling the withdrawal of the flight fine pitch stop and actuated either manually by a lever 200, Fig. 3 which closes a switch 201 in circuit with the solenoid 117a of the valve or by a switch on the undercarriage automatically actuated by the touch down of the aircraft. The first electro-hydraulic valve 101 being in its operative position and supplied with pressure fluid from the pump 86 through a conduit 100, annular space 102 between lands 106, 105 on the slide valve 182 and a conduit 151, fluid from the valve chamber 154 passes to the valve chamber 168 of the second electrohydraulic valve 117 and through a conduit 122 to the left of a piston 124 in an hydraulic relay 172 displacing a valve 173 to close off a drain conduit 129 and open a conduit 55<SP>1</SP>, the third oil line, to a conduit 125 leading from the pump delivery conduit 89. The conduits 112 and 110 may be directly connected to render the operation of the second electrohydraulic valve independent of the first one which, if it fails to function may be overridden by lowering the valve 182 manually by clockwise movement of a lever 84 anticlockwise movement of which raises the valve 182 to feather the blades by directly lifting the constant speed valve 68 against the pressure of its spring 74 : the movement also cuts off the conduit 100 and puts the conduit 151 into communication with a conduit 121 leading to the drain conduit 119. To prevent the blades from drifting into an undesirably fine pitch after the flight fine pitch stop has been withdrawn, an " auto-coarsening " device 320 temporarily increases the pitch if it falls to 2 degrees below the stop point, the device being actuated by a switch 400, Fig. 3 in the propeller hub. The device 320 comprises an electrohydraulic valve of similar construction to the valves 101 and 117, actuation of the valve opening a conduit 326 to the conduit 100 and admitting pressure fluid beneath the piston 318 to raise the speed control valve 68 ; as soon as the pitch is sufficiently increased, the switch 400 opens and the device becomes inoperative. A third stop, for zero pitch, may be controlled by the electro-hydraulic valve 117, the valve being momentarily rendered inoperative, while the pitch is changing from the flight fine pitch stop position to zero, to reset the stops. In this pitch range the autocoarsening device is rendered inoperative by opening a switch 204 controlled by a solenoid 203 in parallel with the solenoid 117a. A fourth electro-hydraulic valve device may control reversal of the pitch by admitting fluid above a piston in a cylinder above the cylinder 329 to depress the piston and its rod to lower the speed control valve 68. This device is associated with the throttle so that it can only function when the throttle is in its reverse position. During normal operation, the pump 86 supplies lubricating oil through a conduit 131, past the relay valve 173 to the " third oil line " 55<SP>1</SP> to the muff X ... X which connects the system to the propeller hub. Specification 742,148, 790,266 [Group XXIII] and 818,701 also are referred to.