GB516613A - Improvements in synchronising and speed-control devices - Google Patents

Abstract

516,613. Automatic control systems. ROLLSROYCE, Ltd., NEWTON BROS. (DERBY), Ltd., NEWTON, F., and ROTOL AIRSCREWS, Ltd. May 11, 1938, No.24069/39. Divided out of 515,934. [Class 38 (iv)] Speed.-In an arrangement for maintaining synchronism between two rotary machines, two alternators, one driven by each rotary machine, supply the stator windings of a single dynamo-electric machine so as to produce two rotating magnetic fields tending to rotate the rotor, which has a closed winding, at a speed corresponding to the difference between the speeds of the two rotating fields, means actuated by the rotor tending to restore synchronism. Fig. 1 shows one form of the dynamo-electric machine in which two stator windings 16 and 17 are each connected to a three-phase alternator. One alternator may be driven by the master engine of a multi-engined aeroplane and the other by a follower engine which is required to run synchronously with the master. The stator windings produce two electromagnetic fields rotating in opposite directions, one at a speed proportional to that of the master engine and the other at a speed proportional to that of the follower engine. A two-element rotor 20 has a winding common to both elements and so wound that any difference in speed between the two rotating fields produces a torque on the rotor, in one direction or the other, which, through the medium of a threaded portion 26 of the rotor shaft, transmits lateral movement to a nut 29 restrained against rotation and fitted to one end of a lever 31 pivoted at 32. The other end of lever 31 engages; by a ball-joint 34, with the end of a valve-rod 35 which may control the supply and discharge of liquid for a hydraulic motor adjusting the pitch of the blades of an airscrew, driven by the follower engine, in such a manner as to tend to bring that engine into synchronism with the master. Flanges 27 and 28 at the ends of the threaded portion of the rotor shaft temporarily arrest the motion of nut 29 to allow for the time-delay between the movement of the nut and the consequent change in blade pitch where there is a wide discrepancy between the engine speeds. Two spiral springs 70, 71, wound in opposite directions restore the rotor to a mean position when the alternators are inoperative. In a modification Fig. 4 (not shown) the threaded portion doesnot extend up to the flanges, so that for heavy torques the nut passes out of engagement with the thread. Fig. 3 is the winding diagram for the rotor, each element of which is two-pole with five slots per pole, the winding on one element being reversed with respect to that on the other to form closed loops which are connected in common to endrings. In a modification, Fig. 5 (not shown) the dynamo-electric machine has a single stator with two windings the absence of slip-rings or brushes eliminating the risk of fire as in the arrangement of Fig. 1.