Patent GB-515934-A (GB)
Title: Improvements in synchronising and speed control devices
IPC: H02P5/50
Filed: 1938-03-19
Abstract: 515,934. Differential governors. NEWTON, F., NEWTON BROS. (DERBY), Ltd., ROTOL AIRSCREWS, Ltd., and ROLLS-ROYCE, Ltd. March 19, 1938, Nos. 8533 and 14110. [Class 57] [Also in Groups XXXV and XXIX] An aircraft screw is maintained in constant speed relation with a datum speed by A.C. generators furnishing frequencies related to the two speeds to a dynamo-electric machine 13a which is operatively connected to means for varying the pitch of the air screw. The datum speed may be that of another engine of the same aircraft. The device may also maintain two air I screws in phase: Three forms of dynamo-electric machine are described namely: one, Fig. 2 with two stators excited by the two frequencies respectively and two rotors on the same shaft having' their windings interconnected in a closed circuit or circuits ; the others, each with a single closed stator and rotor, one having two stator windings and a single closed rotor winding, and the other, stator and rotor windings respectively connected to two generators. The shaft of the dynamo electric machine is restrained against rotation by opposed spiral springs 70, 71 which in the third form referred to may be in triplicate and conduct the three separate phases to the rotor winding. As shown in Fig. 2 the shaft carries a nut 29 on a screw 26, and spring lever 31 pivoted at 32 causes movement of the nut due to speed difference to vary the loading on a valve rod 35 controlling a reversible fluid-pressure servomotor (not shown) adjusting the pitch of the air screw. The valve rod is otherwise subject. to a centrifugal mechanism responsive to the speed of the screws and a spring 48 the tension of which may be varied by a pilot-operated lever 49. When the speed of each of the aircraft engines has, by this lever, been approximately adjusted, the electrical synchronising gear is brought into action by a switch or other means. The spiral springs 70, 71 may be dispensed with if the bending load in the lever 31 is enabled to restore the nut 29 to its mean position for example by using helical splines of quick pitch on the shaft 20. The pitch varying means may be a reversible electric motor controlled by contact associated with the lever 31. In a modification which maintains phase synchronism of the aircraft screws, the dynamo-electric machine shaft drives a drum 77, Fig. 7, having a helical slot 78 in which a tappet-member 79 engages. The speed-responsive centrifugal device may be omitted in some cases and no manual control from the pilot may be necessary. Two piston valves may be provided one controlled by the centrifugal device and the other by the dynamoelectric machine and a change-over valve may bring either into use. Where there are more than two engines switching means may be provided to select any engine as the master by cutting its controlling dynamo-electric machine out of action. The master speed may be that of an electric motor or auxiliary engine. Provisional Specification describes cam mechanism for the tappet which is drven by a mechanical differential driven by two dynamo-electric machines fed by two A.C. generators on engines to be synchronised.