Patent GB-906977-A (GB)
Title: Improvements in aircraft propeller synchronizer systems
IPC: H02P23/00
Filed: 1961-03-22
Abstract: 906,977. Automatic speed control. GENERAL MOTORS CORPORATION. March 22, 1961 [March 29, 1960], No. 10427/61. Class 38 (4). A synchronizing system for aircraft propellers comprises a centrifugally responsive governor valve associated with each propeller and controlling a pitch-adjusting unit. Each propeller drives a three-phase alternator, either of two propellers being selected as a master, and the outputs of the alternators are supplied to circuit 34 for energizing a reversible D.C. actuator motor which rotates at a rate and in a direction dependent upon the difference in speed between the master and slave propellers so as to re-set a governor spring and obtain synchronization between the propellers. A solenoid valve plunger is continuously pulsed on either side of a centre position during operation of a phase synchronizer circuit, the time duration of the pulses being controlled in accordance with phase synchronizing signals derived from the circuit 34. The flow from the solenoid valve biases the governor valve to maintain the desired phase relationship between the blades of the master and slave propellers. Primary winding 82 is energized from one phase of the master alternator, whilst primary windings 84, 86, 88 are energized from the three phases of the slave alternators. The signal induced in winding 92 from the master alternator is out of phase with the signal in windings 104, 106, from the slave alternator except when there is exact speed and phase synchronization, the potential across resistors 120, 122 being proportional to the phase difference. Windings 94, 108, 110 and resistors 132, 134 form part of another phase discriminator in a decrease-speed circuit operating in the same manner as the discriminator of the reset circuit mentioned above. A further phase discriminator comprising the elements 96, 112, 114 and 144, 146, is included in an increasespeed circuit. The voltages developed by the three discriminators have a predetermined phase relationship, dependent upon whether the speed of the slave is greater or less than that of the master. A diode 160 in the reset circuit blocks current through resistor 162 when the output of the discriminator is positive to earth. A Zener diode 164 clips the negative portion of the signal. The decrease-speed and increasespeed circuits are similarly arranged, so that when there is a speed difference between the master and slave propellers, the circuits generate square wave pulses. If a reset pulse has occurred in winding 198 and the slave-speed is less than the master-speed, a pulse from the increase-speed circuit induces a signal in windings 210, 212. A pulse from the decrease-speed circuit follows, but the transformer 200 is not operative until a second reset pulse occurs. The winding 210 is connected through a three-stage transistor amplifier T1, T2, T3 to a field winding 246 of the actuator motor, the signal from the winding 212 being impressed on a three-stage amplifier T4, T5, T6 to excite the other field winding 280. The transistor T1 is cut off by decrease-speed control pulses, the transistor T4 being cut off by increase-speed pulses. Secondary windings 292, 294, 90 and resistors 300, 302 from part of another phase discriminator, the slave signal being displaced 90 degrees from the master signal when the propellers are in phase, the discriminator output voltage being zero. The output from this phase discriminator is applied to an integrating circuit comprising capacitors 318, 320 connected to a push-pull transistor amplifier T7, T8 and T9, T10. The output from terminals 363, 365 is proportional to the speed integral between the master and slave propellers and the phase error rate. This signal is used as the input to the phase synchronizer.