Patent GB-918774-A (GB)
Title: Speed control apparatus
IPC: H02P23/00
Filed: 1959-05-15
Abstract: 918,774. Automatic speed control. SPERRY RAND CORPORATION. May 15, 1959 [June 3, 1958], No. 16831/59. Class 38 (4). [Also in Group XXVII] A helicopter has a variable pitch rotor and collective-pitch adjusting means 14 for the rotor, as well as an engine speed control system with manual and automatic modes of operation. To start the engine 12 for the manual mode of operation, switch 80 is depressed to energize relay 81 and actuate starter 82, clutch 13 being de-energized to disengage the rotor from the engine which is initially unloaded. An output signal from tachometer generator 22 and a signal from collective-pitch function potentiometer 95 are supplied to speed-responsive mechanism 30 so turning the rotor of synchro generator 55 which induces a corresponding signal in the stator of control transformer 56. This rotor is connected to amplifier 61 for driving motor 60 in a direction to eliminate the signal. The speed control system thus eliminates any spurious signals and the speed is synchronized with the manual control to prepare for smooth transition to automatic control. When the throttle control linkage 25 is advanced to rotate an overspeed cam 90, relay 94 is actuated to energize clutches 70 and 74 and lock the linkage 25 to avoid overspeeding the engine during the warm-up period. The main control switch 76 is then opened. After manually positioning the throttle valve 15 by means of stick 14, the switch 76 is re-engaged. When switching to an automatic mode of operation, switch 63 is actuated to connect servomotor 64 to amplifier 61, and to energize relay 77. Actuation of switch 93 engages clutch 13, the servomotor 64 being normally coupled with shaft 71 through clutch 70. To manoeuvre the helicopter in the automatic mode of operation, the stick 14 is moved vertically, and to anticipate the change in speed of the engine due to a change in pitch, in order to maintain a constant rotor speed, such movement simultaneously varies the pitch of the rotor and adjusts potentiometer 95. The signal from this potentiometer is the product of engine speed and a function of the displacement of the stick 14, the output from mechanism 30 being proportional only to the vertical movement of the stick. When the stick 14 is moved in the upward direction, the potentiometer 95 provides a negative signal which is passed through R.C. network 99, 100, to be compared with the speed signal from tachometer generator 22 in summation device 45. The difference signal drives throttle valve 15 to the open position to maintain constant engine speed. When the stick is moved downward, the throttle valve is closed to maintain the engine speed constant with decreased load. The output of summation device 45 is amplified in amplifier 46 to drive motor 47 positioning the rotor of synchro 55 in accordance with the difference between the actual and desired engine speeds. The resultant signal in generator 55 is induced in transformer 56 providing an input signal to amplifier 61. A rate of change signal from generator 50 is fed back to the amplifier 46 and is also connected to amplifier 61. This amplifier drives servomotor 64 coupled to feedback generator 65 and to shaft 71 which is coupled to throttle valve 15. If a gust varies the load on the engine, the tachometer generator 22 corrects the change in speed. A desired change of speed is introduced by actuating switch 20 to energize motor 60 and rotate the rotor of transformer 56. When the valve 15 approaches a closed position, cam 83 actuates switch 85 to disengage clutch 70 and engage clutch 74, so changing the gear ratio of the drive from servomotor 64. To introduce the autorotation mode of operation, the stick 14 must be in a position to ensure low collective pitch before cam 101 closes switch 103. Depression of switch 80 energizes relay 104 to connect bias source 105 to summation device 45. This biasing signal operates through the throttle servo mechanism to decrease the engine speed and disengage an overrunning element of the rotor clutch 13. Specification 918,773 is referred to.