Patent GB-672845-A (GB)
Title: Improved control system for effecting synchronisation and like operations
IPC: H02P5/52
Filed: 1950-05-19
Abstract: 672,845. Correspondence control systems. GENERAL MOTORS CORPORATION. May 19, 1950. [May 24, 1949] No. 12545/50. Class 40 (i). [Also in Groups XXXIII and XXXV] In order to synchronise the speed of a "slave" propeller 2 with that of a "master" propeller 1 (Fig. 1) the propeller 1 drives a three phase alternator having a rotor 22 and stator 24 the voltages developed across resistors 46, 48 and 50 being fed in sequence 120 degrees apart to the grids 38, 40 and 42 of thyratrons V1, V2, V3, whilst the slave propeller drives a second alternator the voltage developed across one phase of which is impressed upon the anodes 84, 86 and 88 of the valves simultaneously through relays 78, 80, and 82 and step-up transformer 52. In operation the pilot's controls 20 for both engines are first adjusted so that the engines are operating at approximately the same speed, the control 20 setting the speed by altering the pitch of the propellers. The voltage impressed upon the grids of the valves VI, V2, V3 from the propeller 1 alternator renders the valves conductive in turn and the propeller 2 alternator places a positive voltage on the plate of each valve simultaneously through its respective relay 78, 80 and 82 at intervals of 360 degrees. Thus, when the engines are in synchronism this plate voltage will coincide with the grid voltage of only one valve causing a pulse of current in one of the windings of a follow up motor 138 every 360 degrees of rotation of the rotor 22, the current pulse being derived from a rectifier system 114, 116 and relay operated contacts 118, 1.26 in the case of the valve VI, a similar system being provided for each valve. The follow-up motor 138 therefore will have a stationary pulsating field and its rotor will remain stationary. If, however, master propeller 1 rotates faster than the propeller 2 the positive pulse on the plates of the valves will first coincide with a positive pulse on the grid of V3 say and will drop back and coincide with a pulse on the grid of V2 so that the valves fire in sequences V3, V2, V1 to create a rotating field for the motor 138 which will operate to decrease the pitch of the propeller 2 until synchronism is obtained. Similarly, it will increase the pitch of the propeller 2 if the valves fire in sequence V1, V2, V3 when the speed of propeller 1 is less than that of propeller 2. If desired the master element may generate a single phase current and the slave element a three phase current as in a second embodiment Fig. 2 (not shown), wherein the master element is an adjustable single phase A.C. generator feeding the grids of the valves whilst the slave elements are propellers each having their own valve, rectifier and follow up motor systems and each driving three phase alternators supplying the plates of their respective valves. Fig. 3 shows the invention applied for control of an aircraft control surface 422, the points A, B, ... H being connected to the left of points A, B, ... H in Fig. 1. The output of a variable frequency single phase oscillator 400 set by potentiometer 402 is compared with that of a three phase oscillator 406 in a manner similar to Fig. 1 any control signal resulting from frequency deviations between the two oscillators being fed to actuator 412 operating the control surface 422 and setting potentiometer 410 to bring the frequency of oscillator 406 into agreement with that of 400. The hydraulic pitch control mechanism for the propellers may be as described in Specification 544,580, [Group XXXIII]. Specification 636,495, [Group XXXV], also is referred to.