Patent GB-846913-A (GB)
Title: Synchronizing mechanism
IPC: B64C11/50
Filed: 1956-12-21
Abstract: 846,913. Automatic speed-control systems. UNITED AIRCRAFT CORPORATION. Dec. 21, 1956 [Dec. 27, 1955 (2)], No. 39086/56. Class 38 (4). Master and slave propellers 12, 12a, Fig. 1, each of which is provided with independent speed control in accordance with the difference between the output of a frequency-sensing bridge circuit 18 fed from a single-phase generator 16, and a reference voltage selected by a potentiometer wiper 17 coupled to the throttle control 84 as described in Specification 757,317 are provided also with electromagnetic impulse generators 14, whereby a correction may be applied to proportional solenoid 22a controlling hydraulic servo mechanism 23a, to remove phase errors between the propellers. The pulses from the master propeller 12 are passed through a selector switch 136 to a sawtooth wave-forming circuit 28 and the sawtooth, output, Fig. 5, is sampled in unit 30 by the pulses from the slave, Fig. 6, to, produce a stepped sawtooth-phase error signal, Fig. 7, which is applied with the speed error signal to input circuit 19a of amplifier 20a. Switch 136 enables the master/slave role of propellers 12, 12a to be reversed. In order to overcome the difficulties arising when the phase error is greater than 2 an off-speed error signal, Fig. 8, developed by the integration of the sudden changes 147 which occur in the waveform, Fig. 7, when the phase error passes through 2 or a multiple thereof, and is combined also with the speed error and off-phase signals in the amplifier input. Positive pulses from generator 14, Fig. 4, which are applied to the grid of valve 44 over transformer 42 discharge condenser 204 and it is recharged via resistors 220, 218 to produce a stable sawtooth waveform, Fig. 5, as an output of cathode follower 46. The sawtooth waveform is sampled in reversely connected valves 124, 126 the grids of which are supplied in common with positive pulses from generator 14a over transformer 130, the output being supplied to the mid-point of resistors 140, 142 in the amplifier input circuit over a cathode follower 132 through " lead " and "lag" circuits 144, 146 and limiting circuits 184, 188. The lead and lag circuits ensure high static sensitivity but reduce dynamic sensitivity with consequent stability. The integrated off-speed error signal is derived by charging condenser 164 through rectifiers 160, 162 in the anode circuit of valve 132 and it is applied through cathode follower 150 to conductor 153a whereby it is combined with the off-phase signal at the output of limiters 176. The voltages applied to tube 150 may also be selected to effect limiting. The speed signal from generator 16a detected in bridge 18 is applied over contact 74 of relay 240 to the junction of resistors 78, 80, and the composite signal is amplified in a chopper amplifier 20a, negative feedback being provided over resistor 92. The amplifier output is applied to the proportional solenoid 22a and controls the input to the chamber 113 on the upper side of the piston 106 to move the cylinder 108 to change the propeller pitch through a gear train which actuates a distributer valve with follow-up. The fluid servo mechanism includes a low-pitch stop 244 and when the throttle lever is placed anywhere between idle and full reverse, Beta solenoid 252 is energized to remove the mechanical low-pitch stop and operate relay 240 over switches 256 and 118 to earth the off-phase and off-speed signal and switch to Beta control whereby the voltage on a potentiometer 26a is compared with the voltage of potentiometer 24a, the wiper of which is driven by the servomotor and is indicative of the propeller pitch, so that the propeller pitch is moved in correspondence with the throttle in the manner described in Specification 738,624. Facilities for feathering and unfeathering are provided. Specifications 656,208, 678,505, 692,119 and 822,564 also are referred to.