Patent GB-679187-A (GB)
Title: Improvements in and relating to duplicated servomotor systems
IPC: B64C13/00
Filed: 1949-05-09
Abstract: 679,187. Fluid-pressure servomotor-control systems. BOULTON PAUL AIRCRAFT, Ltd., and NORTH, J. D. May 8, 1950 [May 9, 1949], No. 12299/49. Class 135. In a duplicated servomotor system in which two motors drive a common output member and the two motors also drive in opposite senses two input elements of a differential so as to detect differences in speed between the two motors, the output signal from the differential is applied in opposite senses to two individual control means for the two motors so as to decrease the speed of the faster motor and increase the speed of the slower. The invention is shown applied to the actuation of an aircraft control surface from a pilot's control column. The latter is connected through a linkage 19 to the ends of two floating levers 15 which are fulcrummed on pivoted cranks 9 and are connected at their other ends to the pistons of jacks 1, 2 so that movement of the pilot's control column causes, initially, cranks 9 to make the small movements allowed by stops 12, 14. Such movement is imparted through togglelinks 37, 39 to hydraulically-operated servo-mechanisms 7, 8 which control variable-delivery hydraulic pumps 5, 6 of the rotating radial piston type, the output of the pumps being to the jacks 1, 2. The pistons of the latter are connected through a rocking arm 3 and a push-pull device 4 to the aircraft control surface. The movement of the jack pistons is repeated back to the floating levers 15 through levers 20, 21, and links 17. The pressure-fluid supply for the servo-mechanisms 7, 8 is obtained from separate banks of pistons in the pumps 5, 6, such banks being spring-loaded into an eccentric position. Levers 20, 21 are connected to the input members 24, 27, respectively, of a differential, the lever 21 being connected through gearing 25 so that, on movement of the jack pistons, the members 24, 27 rotate in opposite directions. Should the speeds of the two pistons be out of alignment, the difference will be detected by the planet carrier 28 and communicated through a pinion 31, rock shaft 32, levers 33, 34, and links 35, 36, to the mid points of the two toggle mechanisms 37, 39. As the links of the toggle mechanisms are normally biassed in opposite directions, the resultant movements imparted to the servo-mechanisms 7, 8 will be in opposite senses and the control chains will apply correcting signals to the jacks to bring their speeds into alignment again. In the event of failure of one jack, a bye-pass valve therefore, which is normally held closed by pressure from the corresponding pump, will be opened and the faulty jack will idle. The lever 3 would also be provided with a lock held in the disengaged position by pressure from the two pumps but, on failure of one system, the lock would be freed and the lever 3 thus prevented from rocking. A switch, operated from the lever 3 or from the differential gear, may be provided to switch off the slower pump in the event of the jacks becoming out of step by an excessive amount. The invention is applicable to the control of electric motors instead of hydraulic jacks, and the differential gearing may be replaced by a lever differential.