Patent GB-580176-A (GB)
Title: Improvements in and relating to vibration damping devices
IPC: H02K49/02
Filed: 1943-05-06
Abstract: 580,176. Torsional vibration-dampers. TUSTIN, A., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. May 6, 1943, No. 7222. [Class 108 (iii)] [Also in Group XXXV] A torsional vibration - damper comprises co-operating toothed magnetic members 3, 5 one of which is mounted on or coupled with the shaft 1 or other rotatable part liable to vibrate torsionally while the other member is rotatable relatively to the first member and forms or is coupled with a vibratable mass, excitation arrangements being provided for causing magnetic flux to pass between the teeth of the members the tooth pitches of which are different from one another and a winding or conductor system being provided on one or each of the members in which currents are induced by movement of the flux distribution relatively thereto on relative movement of the members. As shown, both members 3, 5 are of laminated construction and are secured respectively to a solid magnetic member 4 on the shaft 1 and to a cylindrical casing 6 of magnetic material mounted on the shaft by end discs 7 and bearings 8. An annular permanent magnet 9 secured to the casing 6 is spaced by an air gap from a corresponding surface 10 on the member 4 and is polarized radially to cause magnetic flux to pass over the space between the members 5, 3 and to return by the surface 10. The pitch of the teeth of the member 3 is slightly less than that of the member 5 and damping conductor systems are mounted on the members comprising squirrel cages 11, 12 the bars of which are located in the slots between the teeth so that flux variations in the teeth induce corresponding currents in the conductor systems. The degree of alignment of each tooth of the outer member 5 with the adjacent tooth of the inner member 3 varies in cyclical manner around the air space between the members for a given relative position of the members, forming four alternate zones of high and low reluctance of the air space. A movement of the inner member by one tooth pitch relatively to the outer member causes a rotation of the flux distribution through half a revolution thus inducing corresponding current in the squirrel cages 12, 11 respectively which resist the relative movement of the members. The damping conductor system may be omitted from one of the toothed members. In a modification the permanent magnet 9 is replaced by an annular exciting coil surrounding the members 4 and connected by slip rings on the shaft 1 or the casing 6 co-operating with brushes supplied with current from any suitable source. In a further modification, the members 3, 5 are duplicated, the further members replacing the magnet 9 and the portion 10 of the member 4, the device being excited either by an annular coil or by an annular permanent magnet. Where homopolar excitation of the damper is undesirable due to liability of the shaft, excitation arrangement may be such as to provide heteropolar excitation of the damper. For example, one pair of diametrical slots in one of the members 3, 5 may be of larger size than the remaining slots to accommodate a pair of exciting coils, similar to the arrangement described in Specification 557,968, [Group XXXV].