Patent GB-1110866-A (GB)
Title: Improved hysteresis damper
IPC: F16F15/18
Filed: 1966-07-11
Abstract: 1,110,866. Hysteresis damper. GENERAL ELECTRIC CO. 11 July, 1966 [30 Dec., 1965], No. 31013/66. Heading F2S. A hysteresis damping device, which provides a substantially constant damping force for displacement away from a neutral position and, at the same time, reduces the force to substantially zero in the immediate vicinity of the neutral position, comprises a disc 12 which is made of non-magnetic material, e.g. aluminium alloy, is mounted on a rotatable shaft 14 supported by a combined bearing bracket 15, and carries, on its upper face, regions of high and low hysteresis magnetic material 16, 16a, 18, 18a and 22, 20, 20a, 22a comprising respectively approximately 2 and 5% by volume of magnetic oxide and carbonyl iron in a plastics resin matrix. The regions 16, 16a and 22, 22a are annular sectors the regions 18, 18a decreasing linearly from the width of the regions 16, 16a to zero and the regions 20, 20a increasing linearly to the junction point of the regions 20, 20a which is diametrically opposite the junction 18, 18a and where there is provided a small amount of additional low hysteresis magnetic material 24. Substantially horizontal strong and weaker magnetic fields for the high and low hysteresis magnetic material are provided respectively by magnet assemblies 26, 40 which are supported on the bracket 15. Movement of the high hysteresis magnetic material regions 16, 16a of uniform cross-section between the magnet assembly 26 causes a constant magnetic drag which is not accompanied by any magnetic torque tending to drive the disc to any particular position. When, however, the regions 18, 18a of varying cross-sectional area, move between the magnet assembly 26 besides causing a corresponding continually increasing or decreasing magnetic drag according to the direction of movement there is also produced an unstabilizing directional torque which tends to move the disc 12 away from the neutral position at the junction of the regions 18, 18a. This unstabilizing torque is opposed by a stabilizing torque which is produced as the corresponding low hysteresis portions 20, 20a, of varying cross-sectional area, move, with lower hysteresis drag, between the magnet assembly 40. By adjusting the magnetic field of the magnet assembly 40 the stabilizing torque can be made slightly greater than the unstabilizing torque so that the disc is biased towards the 'null' position. The magnet assembly 26, Fig. 2 not shown, comprises upper and lower pairs of nickel cobalt bar magnets (28, 30) and (34, 36) separated respectively by non-magnetic spacers (32, 38) and providing a field of 1100 gauss in the vicinity of the disc. The somewhat similar magnet assembly (40), Fig. 3, not shown, produces a maximum field of 750 gauss which can be varied by the introduction or withdrawal of steel spacers (46, 52). Regions 22, 22a are provided because it is not desirable for the regions 20, 20a to end in finely tapered points. In alternative arrangements the hysteresis magnetic material can be linear rather than circular e.g. linear plastic matrices can be wrapped around a circular cylinder and magnet assemblies such as 26, 40 can be applied at the end of the cylinder. Damping of linear motion can also be provided by applying linear matrices to a straight strip of material passing between the poles of magnet assemblies. It is also possible to superimpose the matrices carrying the magnetic oxide and the carbonyl iron so that a single magnet assembly can provide magnetic field for both. In this arrangement the relative magnitudes of the torques are not adjustable.