Patent GB-678505-A (GB)
Title: Synchronizing apparatus
IPC: H02P5/52
Filed: 1948-07-21
Abstract: 678,505. Automatic speed control systems. OFFNER, F. F. July 21, 1948 [July 25, 1947], No. 19529/48. Class 38 (iv). A phase and/or speed governor system for a rotating member, e.g. an aircraft engine, comprises generators for producing a repetitive wave and a pulse wave the phases of which are to be compared, one of the generators being driven at a constant frequency and the other at a frequency varying with the speed of the rotating member, the arrangement being such that after the phase comparison of the repetitive wave and pulse wave a control voltage is produced which is used to adjust the speed of the rotating member so as to maintain a preselected phase relationship between the two waves. As shown in Fig. 1 an aircraft engine A drives a three-phase tachometer generator 1, the output from which is rectified and fed to a condenser 5 (Fig. 2). A steady D.C. voltage derived from the +28 v. terminal via a regulator tube 8 and smoothing circuit 12 is also fed to the condenser 5. At a predetermined engine speed the resultant voltage across the condenser 5 is zero, but upon a deviation the voltage across condenser 5 varies in polarity and magnitude proportionally to the sense and magnitude of the deviation. Assuming a deviation the control voltage across condenser 5 is fed to the fixed contact 14 of a vibrator S comprising fixed contacts 14, 15, vibrating contact 16, and energizing coil 17. Vibrator S serves to " chop the control voltage into impulses which are fed through amplifiers 23, 25, 26 and 27 to a transformer 28. The control voltage appearing across the recording of the transformer 28 is fed via a second vibrator S<SP>1</SP> ganged to the vibrator S, to the terminals X, Y, and the impulses appear across the coils 38a, 38b of a proportional solenoid 38 (Fig. 1) which serves to adjust the pitch of the propeller of engine A in a sense to restore the speed of the engine to the prede. termined value. The proportional solenoid 38 operates a pilot valve 39 which controls the flow of oil to propeller pitch-adjusting mechanism 48. The speed of further engines, e.g. B, may be controlled in a similar manner. In order to prevent hunting a voltage proportional to engine acceleration is added by differentiating the speed voltage derived from the generator 1 in a network 6, 7 (Fig. 2). In addition to the speed control the relative phases of all the propellers are also maintained constant. The output from the generator 1 is also fed through a adjuster phase shifter 61 to a pulse generator 63 of known type. The pulse output of the generator 63, which is of a frequency corresponding to that of the propeller revolutions is fed to a phase comparator 69, together with a saw-tooth wave of fixed frequency from a saw-tooth generator 51 also of known type (Fig. 3, not shown). A stepped voltage is derived from the phase comparator 69, the amplitude and polarity of which correspond to the amplitude and polarity of the saw-tooth wave at the instant of occurrence of each pulse from the generator 63 and are proportional to the phase difference at the start of each cycle. This voltage is developed across a condenser 74 (Fig. 2), and passed through resistors 77, 78, and condenser 79 in parallel in order to partly differentiate the voltage to prevent hunting. A positive D.C. voltage is inserted through resistor 80 and adjusted so that the total voltage at the junction 83 of resistors 77 and 78 is zero when the propellers are in the correct phase relationship. The control voltage derived upon a deviation of phase is fed to the lower fixed contact 15 of the vibrator S, and hence through amplifier 23, 25, 26, 27 and transformer 28 to solenoid 38. Solenoid 38 operates the propeller pitch changing mechanism in a sense to correct the phase deviations. Owing to the action of the vibrator S the speed control voltage and phase control voltage are fed alternately to the solenoid 38. If desired the saw-tooth generator may be driven from the engine while the pulse generator is driven at a constant frequency.