Patent GB-641511-A (GB)
Title: Improvements in and relating to shock absorbers and movement dampers
Inventor: ELSOME-JONES RONALD JOB
IPC: F16F6/00
Filed: 1948-02-16
Abstract: 641,511. Shock absorbers; spring suspensions. AUTRONIC DEVELOPMENTS, Ltd. Feb. 16, 1948, No. 4450. [Classes 108(ii) and 108(iii)] A movement damper or shock absorber comprises a magnet and an armature of magnetic material, or a pair of magnets restrained against relative rotation about a common axis jointly by friction between their juxtaposed surfaces and the magnetic attraction between them; wherein.the magnetic attraction is rendered greatest at a pre-determined relative position of the surfaces, say the neutral or mean position of the damper, by the provision of cooperating recesses or interruptions in the magnetic material of the juxtaposed surfaces, so arranged that the overlapping areas of the magnetic portions of the surfaces and the cross, area of the magnetic flux path are gradually reduced when the magnet and armature, or the two magnets, are rela'tively rotated in either direction away from the pre-determined position. In the arrangement according to Fig. 3, a circular electromagnet 16 and a soft iron disc armature 17 are housed in frictional engagement between a base plate 18 and a casing 20. The armature 17 is keyed to a spindle 23 for free rotation relative to the electromagnet 16, which is keyed on to the base plate 18 by means of ribs 29 on the electromagnet and cooperating grooves 30 on the base plate. The electromagnet is provided with an annular groove 32 for a winding 33 and radial grooves 34 which latter, together with corresponding radial grooves in the armature 17, cooperate to reduce the magnetic flux path between the electromagnet and the armature when their relative angular position varies from a mean position, during the operation of the damper. The damping effect is rendered proportional to the relative speed'of movement of the electromagnet and armature by a ring 37 of electrically conducting material inset into the armature 17. In the application to a wheel suspension for a road vehicle, Fig. 1, in which a wheel 2 is carried by a link 10 connecting the outer ends of a pair of wishbone arms 4, 5 pivoted to a frame member 1 and in which a helical spring 12 is mounted between a projection 1A of the member 1 and the lower arm 4, the upper arm 5 is connected directly to the spindle 23 of the damper, the base plate 18 of which is secured to the frame member 1. The energizing circuit for the winding 33 may be interrupted by any suitable means when the damper is required to be inoperative and such means may include a switch operated by a device responsive to rotation of the vehicle wheels. Also, the energizing circuit may include a manually controllable variable resistance which may additionally or alternatively be controlled automatically by deflections of the vehicle spring to vary the friction of the damper in accordance with variations in spring deflection. The damper friction surfaces may be of case hardened steels or formed from a deposit of hard metal. In a modification the electromagnet and armature may be cylindrical and mounted concentrically, the winding 33 and a ring 37 being disposed round the opposed cylindrical surfaces. Alternatively, the magnet and armature may be plates of irregular shape relatively rotatable on separate axes or on a common axis. In a further modification a concentrically-disposed magnet and armature may be arranged for relative reciprocating movement. Alternatively, a suitably shaped armature may be arranged to move within and along a groove provided in the face of a magnetic member.