Patent GB-541839-A (GB)
Title: Improvements relating to hydraulically-actuated variable-pitch screw propellers
IPC: B64C11/42
Filed: 1940-06-05
Abstract: 541,839. Fluid-pressure servomotor control systems. ESCHER WYSS MACHINENFABRIKEN AKT.-GES. June 5, 1940, Nos. 9835 and 9836. Convention dates, June 22, 1939 and July 10, 1939. [Class 135] [Also in Groups XXXIII and XXVI] In hydraulically-actuated, variable-pitch screw propellers in which the blade adjustment is normally confined to a relatively small pre-set pitch range while further adjustment of the blades into a feathering, braking or other extreme position is possible only after an increase in the hydraulic control pressure has been brought about by deliberate manual operation of the control mechanism, one or more control members interrupt the supply of pressure medium to the pitch-adjusting means proper at the limits of the pre-set pitch range, while the further adjustment is possible only after the increased hydraulic control pressure has opened an auxiliary cut-off device for the pressure medium. As shown, each blade holder 8 is rotated by a link 6 coupled to a servomotor formed by a double-acting cylinder 5 movable axially over a piston and fixed on a central guide tube 3 formed with passages 11, 12 for the supply and exhaust of pressure oil to and from the cylinder chambers 13, 14, rotation of the cylinder being prevented by a spline 15. The cylinder 5 carries with it a control rod 16 having an ungrooved part 19 between grooved end parts 17, 18, whilst the piston 4 carries a locking device 27 which is urged by a spring 28 to engage the inner wall of the cylinder. To increase the pitch of the blades, pressure oil admitted to the passage 11 passes through a port 29, the grooves 17, and ports 30, 31 into chamber 13 to raise the cylinders, the pressure oil leaving chamber 14 through a spring-loaded, non-return valve 25 and port 20 to passage 12. At the limit of the pre-set pitch range, the smooth part 19 of the control rod 16 interrupts communication between the ports 29, 30, and the spring 28 forces the locking device 27 outwardly as a fine bore 37 in a port 35 of this device allows the enclosed oil to escape. If oil under higher pressure is supplied to the passage 11, it opens a spring- loaded overflow valve 32 in port 29, byepasses the control rod 16, and enters the port 30. The locking device is moved inwards and the oil flows through port 31 into chamber 13, to further raise the cylinder 5 until it reaches a stop 51. A similar series of operations takes place when the pitch is decreased within the pre-set and extreme positions by means of the grooves 18, a spring-loaded non-return valve 34, and a spring-loaded overflow valve 23. The control rod or rods may be arranged outside the cylinder, or they may be replaced by valves controlled by the relative positions of the piston and cylinder. The flow of pressure oil to and from the passages 11, 12 is controlled by the pivoted weights 81 of a centrifugal governor driven through gearing 86 from the propeller driving shaft 11, the weights 81 being connected by links 92, a cross-bar 93 and a stiff spring 94 to a governing spindle 89 which controls pipes 111, 121 connected to the passages 11, 12. The prescribed stroke for this spindle is limited by stops 87, 88 on the governor casing 83. An abutment 97 on a spring cup 98 co-operates with a stop flange 96 on the cylindrical extension of an abutment plate 95 for the governor spring 82, and the plate 95 can be moved to vary the force exerted by the spring 82 by some external operation, such as a hand lever 60, a cable 192, a pulley 191, and a screw-threaded rod 201. The pressure oil is supplied by two pumps 32<SP>1</SP>, 33<SP>1</SP> associated with a spring-loaded, non-return .valve 47 and an overflow valve 39 which is loaded by a spring 391, and which can be lifted by means of rods 40 to cut out the hydraulic control of the blade pitch. The pumps 321, 331 are normally shortcircuited to the suction branch 341. If the speed increases or decreases the centrifugal weights 81 move the spindle 89, but the pump 33<SP>1</SP> remains short-circuited and the pump 321 supplies pressure oil either to the pipe 11<SP>1</SP> or the pipe 121, and connects either the pipe 121 or the pipe 11<SP>1</SP> to the suction branch 341. If the plate 95 is deliberately moved for adjusting the blades into a feathered position, the flange 96 engages the abutment 97 and the weights 81 are arrested by the stop 87, further movement of the spindle 89 then being permitted by yielding of the spring 94 so that the spindle acts as a change-over valve. Oil from the pump 33<SP>1</SP> opens the non- return valve 47 and is added to that delivered by the pump 321, The higher pressure oil also acts through channel 44 to a surface 42 on the piston 41 of valve 39 to supplement the action of spring 391. A similar series of operations takes place when the plate 95 is deliberately moved for adjusting the blades to a braking position by means of the stop 88 and a face 43 on the piston 41 of area equal to that of the surface 42. In a modification, the governing member and the change-over member are constructed as separate units though they also may be housed in a single casing. As shown in Fig. 6, the handle 60 for actuating the transmission cable 192 has three ranges of movement indicated as 48, 49, 50 on a plate 51, and is brought to its mid-position by springs 52, 53. Within the normal working range 48 the lever can be moved by hand. into any desired intermediate position in which it is self-locking by means of a spring-controlled pawl 55. To change to either of the feathering or braking ranges 49, 50 the pawl 55 must be depressed beyond the radial length of shoulders 57, 58 by deliberate actuation of a press-button 54.