Patent GB-546197-A (GB)
Title: Improvements in or relating to variable pitch propeller control
IPC: B63H3/10
Filed: 1940-05-02
Abstract: 546,197. Fluid-pressure servomotor control systems. STEVENS, A. H. (Hammond, jun., J. H.). May 2, 1940, No. 4264/41. Divided out of 551,302, [Group XXII]. [Class 135] [Also in Group XXXIII] In a system for maintaining under varying conditions a constant thrust upon a propeller shaft bearing or, equivalently, a constant power output from the driving motor of a water or other craft, the pitch of the propeller blades is varied automatically by control mechanism which is directly responsive to changes in the thrust upon a thrust bearing for the propeller shaft. As shown, the pitch of the blades 13, which are driven from a prime mover 20 through a shaft 15, is controlled by a rod 19 passing through the shaft 15 and displaceable under the action of fluid acting upon a piston 27 in a cylinder 27a, the piston 27 being actuated by the displacement of fluid in a circuit compressing pump 26, valve 25, reservoir 36, distributer 25a and cylinder 27a. The position of the valve 25 is regulated by a motor 21 connected to the upper end of a floating lever 23, a central point of which is connected to a valve operating-lever 24, and the lower end of which is associated with a sliding collar 29 movable in unison with the piston 27. The upper end of the lever 23 actuates by a wire 30 a propeller pitch-indicator 31, the reading of which corresponds with the position of the collar 29 and piston 27. The motor 21 is arranged in three alternative circuits including a battery 82, three-way swtch 83, an adjustable rotatable disc 52 incorporating contact segments 61 ... 66 and an insulating portion between the segments 63, 64, a pointer 53 connected to the centre contact of the switch 83, and resistances 76, 77, 80, 81 for providing a restoring current of desired magnitude. The position of the pointer 53 is controlled by the fluid pressure in a cylinder 46 which is supplied with working fluid by a manually-operated pump 48. The propeller shaft 15 passes through a thrust bearing 17 comprising collar 40 and shoe 41 which is engaged by thrust pins 42, these in turn cooperating with pins 43 engaging a piston 45 reciprocable within the cylinder 46, the propeller thrust thus being balanced by the pressure in the cylinder 46, which itself controls the position of the pointer 53. The disc 52 is adjustable by means of a hand-knob 60 and the engine 20 is preferably controlled by a constant-speed go,vernor. In the operation of the device, the switch 83 is first moved on to its upper or lower contact to complete a circuit through the motor 21 and to adjust the pitch of the propellers as indicated at 31 to the desired value. The craft is next brought to its desired speed and at this stage the hand-knob 60 is rotated so that the insulation between segments 63, 64 is brought below the pointer 53, and the arm of the switch 83 is moved to central position. Should the craft encounter more adverse or more favourable conditions, the resistance to the propellers is increased or decreased, the pressure on the bearing 17 and in the cylinder 46 rises or falls, and the pointer 53 moves on to one or other set of circuits completing contacts 61 . . . 63 or 164 . . . 66, the motor 21 is driven at an appropriate speed to actuate the lever 23 and valve 25, the fluid circuit is put into operation and the piston 27 actuates the rod 19 to cause the requisite decrease or increase in the propeller pitch, with a consequent restoration of the pressure in the cylinder 46 to the selected value; and the power output of the engine is normal. Following this, the pointer 53, motor 21, lever 23, collar 29 and indicator 31 assume a fixed relation corresponding to the changed conditions encountered.