Patent GB-836941-A (GB)
Title: Improved control system for a plurality of variable pitch propellers
IPC: H02P5/50
Filed: 1957-12-06
Abstract: 836,941. Automatic speed-control systems. GENERAL MOTORS CORPORATION. Dec. 6, 1957 [Dec. 24, 1956], No. 38003/57. Class 38 (4). In a control system for a plurality of variablepitch propellers each of which has an adjustable speed governor to control propeller pitch to maintain the propeller speed substantially constant, and a generator for producing a signal indication of speed and phase, the system includes for each propeller a speed comparator for the speed signals from one master and the respective slave to develop a speed error signal, a phase comparator to develop a phase error signal, a manually-operable selector to select one or the other signals, and means to adjust the speed or phase according to the signal selected. Slave propellers 10, 12, 13, Fig. 1, are maintained at the same speeds and may be in phase with propeller 11 by motors 24 the threephase, four-pole stations of which are energized by two-pole, three-phase tachometer generators 22 driven from the respective propellers through a 4:1 reduction gearing 20 and the rotors by the alternator 22, of the master propeller 11. Propeller 12 may be alternatively selected as master by switches 25, 27. Speed is corrected by a reversible motor 18 which adjusts the loading on a centrifugal governor, Fig. 4 (not shown), the fields 50, 52, Fig. 2, of the motor 18 being energized by the discharge of a condenser 44 through segments 37 or 36 respectively of a statis commutator around which a brush 43 is driven by the motor 24. The condenser is charged during rotation of the brush 43 through line 47 and segment 38 when synchronizer " on " "off " switch 48 is closed. Maximum and minimum limit switches 49, 51 designed to operate at 1040 R.P.M. and 1000 R.P.M. respectively are provided and switches 55 which are interlocked with switches 48 enable the motor to drive the governor to the mid-speed position, the position being set by switches 53, 54 which open at 1020 R.P.M. A governor sensitivity checking arrangement is provided by manual switch 57 and upper high limit switch 55. Phase correction is provided by the closure of a switch 60 which energizes motor 65 through wipers 11, 64 on commutator 33, to integrate the phase error and provide an indication thereof by driving wiper 66 around potentiometer 34, the resistance winding of which is itself rotated by speed error motor 24. The potentiometer 34 is connected through the contacts of a relay 136, Fig. 3b, to form a bridge with resistor 114 and the bridge output together with the amplified output from a phase discriminator stage V2, Fig. 3a, which is fed with one phase of the respective tachometer generator output is applied together with a differential function to control the duration of successive pulses from a multivibrator V4. The pulses are applied through an amplifier V5 and thyratrons V6, V7 to differentially control a solenoid-operated valve 166-174, Fig. 5, in parallel with pitchcontrol valve 150, and phase correction is thereby effected. The entire valve block is rotated and the centrifugal force on piston 150 is opposed by spring 153 acting on lever 151. Ring 162 is advanced by motor 18 through screw 169 and gearing 159, 160 and speed control is effected by cam 164 acting on roller 165. Specification 810,453 is referred to.