GB574074A - Improvements in or relating to mountings for vibratory bodies - Google Patents

Abstract

574,074. Resilient mountings. BRISTOL AEROPLANE CO., Ltd., and BERRY, P. E. Dec. 30, 1943, No. 21863. [Class 108 (iii)] [Also in Group XXXIII] A vibration-damping mounting for an aeroengine or other apparatus comprises two sets of elastic devices; torsiona and angular vibration are each separately controlled by the two devices, whilst linear vibra tion is controlled jointly by both. One of the devices functions in two directions with differing resilience, and th three modes of vibration can thus be decoupled, i.e. suitabl resonant frequencies can be in dividually selected for each mode. In Figs. 1 and 3, radial aero-engine 12 is mounted on a frame ring 11 by fou groups of links. Each group comprises an integral outer pair 18 pivotally connected at 19 to the engme, and a single inner link 22 connected with the engine by a universal joint 23. The frame ends of the links are fitted with rubber bushes 24a, 24b and are carried between brackets 14 on frame 11 by a hinge pin 16. Bushes 24a of the outer links 18 deflect axially as well as radially, and have snubbing discs 27 ; bush 24b of the centre link 22 deflects radially only. The directions of the outer links 18 converge at the centre of gravity Z of the engine, whilst the inner links converge at a point O on the engine axis in front of the centre of gravity. Torsional vibration is absorbed by axial deflection only of the rubber bushes 24a of the outer links 18, the universal joints 23 preventing torsional vibration reaching the inner links 22. The stiffness of bushes 24a under axial deflection is therefore given a value for a suitable resonant torsional frequency. Angular vibration occurs about the centre of gravity Z, and is not transmitted to links 18 since they converge at that point, but is received by the inner links 22 and absorbed by radial deflection of bushes 24b. The stiffness of these bushes under radial deflection is likewise given a value for a suitable resonant angular frequency. Linear vibration in a plane normal to the engine axis is transmitted to all the links and is absorbed by radial deflection of all the bushes as well as by axial deflection of the outer bushes 24a. A suitable resonant linear frequency is obtained by selecting a value for the one remaining stiffness : that of the outer bushes 24a under radial deflection. In the modification of Fig. 2 (not shown), the outer links 18 converge at a point on the engine axis behind the centre of gravity. The arrangement functions in substantially the same manner as that of Fig. 1. Equations relating to the three values of stiffness with other dimensions in order to obtain decoupling are given.