Patent GB-661121-A (GB)
Title: Improvements in electromagnetic friction vibration dampers
IPC: F16F15/129
Filed: 1948-12-06
Abstract: 661,121. Vibration-dampers. POWNALL, G. H. DU. T. Dec. 6,1949 [Dec. 6. 1948 ; March 1, 1949] Nos. 31500/48 and 5484/49. Class 108(iii). An electromagnetic friction vibration damper comprises two magnetic elements respectively an electromagnet and an armature co-operating therewith to apply force to the working friction elements of the damper, the armature being mounted so as to be freely slidable on a shaft axially of the electromagnet, one of the magnetic elements being provided with screwthread formations engaging a screwthreaded member angularly movable relative to the other magnetic elements, cooperating adjusting friction members associated with the two elements to engage them for rotation on reaching a predetermined minimum working distance, and ratchet mechanism engaging the screw-threaded magnetic element so that the adjusting friction members are effective only to separate the armature and the electromagnet to keep a substantially constant working air gap. In the arrangement shown in Fig. 1, (31500/48), as applied to a shock absorber for a vehicle suspension, an armature f is slidably mounted on a splined portion d<SP>1</SP> of a shaft d which is rotatable within a casing consisting of a rear part a and a front part b. An electromagnet g is screwed on to a hub a<SP>2</SP> of the part a (shown in the upper part of Fig. 1), or, in a modification, is screwed on to the part a, (as shown on the lower part of the Figure) and carries at its rear end and is insulated from, a ratchet ring j which engages a spring-loaded plunger k. A friction assembly comprising friction discs h and interspaced plates e<SP>1</SP>, f<SP>3</SP> and f<SP>4</SP> on the periphery of the armature f, engages a friction plate e secured between the rear and front parts a and b of the casing. A ring f<SP>5</SP> of friction material stands just proud of the face of the armature f and in the loaded position of the friction assembly, as shown, engages lightly the complementary face of the magnet g. In operation of the damper, wear on the friction assembly causes the ring f' to impart a frictional drag on the magnet g, which due to the engagement of the plunger k with the ratchet ring j, is rotated along the hub a<SP>2</SP> (or along the screwed part of the casing) away from the armature f until the frictional drag is insufficient and the predetermined clearance between the magnet and armature is restored. A light spring m takes up backlash in the screwthreads. The plunger k forms one terminal for the winding of the electromagnet, one end of which is connected to the ratchet ring through an insulated bolt j<SP>1</SP> the other end being " earthed" to the magnet. In the arrangement shown in Figs. 1 and 2 (5484/49), a shaft 13, rotatable within rear and front parts 10 and 11 respectively of a casing carries on its central portion a screwed hub 15 having a flange 16. An armature 17 is adjustably mounted on the hub 15 and is complementary to an electromagnet 18 fixed within the rear part 10 of the casing. A ring 23 of friction material is located on and stands proud of a recess on the outer face of a bobbin 20 housing the magnet winding. The periphery of the flange 16 which is partspherical engages a self-aligning thrustring 24, and a hub 17<SP>1</SP> of the armature 17 carries a toothed ring 17<SP>2</SP>. A carrier 26. rigidly secured to the shaft 13, is splined on its outer periphery to carry a multiplate friction disc assembly comprising inner and outer plates 27 and 28, friction rings 29 and a thrust ring 30. Cranked levers 32, Fig. 2, rotatably mounted in lugs 31 cn the face of the carrier 26, engage at their inner ends 32', the back of the ring 24, and at their outer ends 32<SP>2</SP> are halved to engage the ring 30. A ratchet spring 34 on the carrier 26 engages teeth 17<SP>3</SP> on the ring 17<SP>2</SP>. In operation of the damper, the friction disc assembly is loaded through the ring 24, levers 32 and thrust ring 30. Wear on the friction-disc assembly effects unidirectional rotation of the armature on the hub 15 against the holding action of the ratchet spring 34.