GB756107A - Improvements in and relating to shock absorbers or dampers - Google Patents

Abstract

756,107. Shock-absorbers and dashpots. NATIONAL RESEARCH DEVELOPMENT CORPORATION. July 22, 1954 [July 29, 1953; Dec. 29, 1953], No. 21450/54. Class 108 (3). A device for damping the movement of a body relative to another body comprises a fluid containing in suspension a particulate ferromagnetic material, means for producing a magnetic field across at least a part of the fluid, means for causing a displacement or shearing of said part of the fluid on relative movement between the bodies, and means for varying the magnetic field in response to either velocity or acceleration of one body relative to the other. In Fig. 2, the cylinders 13, 13, of a double-acting vehicle shock-absorber, are connected by a passage P surrounded by a solenoid 9 contained in an iron casing 8 having a brass insert 10. Tapered iron rods 11, 11, combine with a double-conical iron boss 12 to define conical passages 21, 21. These passages may be spaced apart and connected by a passage of reduced diameter. The shock-absorber is filled with a magnetizable liquid which may comprise carbonyl iron particles in suspension in silicone or hydrocarbon oil. The solenoid 9 is connected via an energizing battery 44 (Fig. 5) to the centre tap and slider 80 of a rheostat R<SP>1</SP>, R<SP>2</SP> in a device 36. The slider 80 is connected through a conventional dashpot 92 to a lever arm 90 which carries an inertia mass 41. The lever arm 90 is fulcrummed on a part connected to the vehicle axle assembly, and the rheostat is mounted on the vehicle chassis. In operation, when the axle receives an upward acceleration, the upward movement of the axle is transmitted via the arm 90 and dashpot 92 to the slider 80. This reduces the damping effect by reducing the current flowing in the solenoid 9. Due to the inertia of the mass 41, and the leverage of the arm 90, there is a magnification of the axle movement. The slider deflection thus depends upon the acceleration of the axle. When the latter moves without appreciable acceleration, the deflection of the slider depends upon the velocity of the axle (due to the action of the dashpot 92). As axle movement ceases, a spring 78a returns the slider 80 to its central position. This ensures maximum damping at extremes of deflection. The dashpot 92 may be replaced by an eddy-current device. The slider operates on the winding R<SP>1</SP> of the rheostat for upward axle movement, and on the winding R<SP>2</SP> for downward axle movement. In a modification (Figs. 4 and 6) not shown, the windings R<SP>1</SP> and R<SP>2</SP> are connected to respective solenoids which are disposed around the respective cylinders of a double-acting damper. Each solenoid controls the flow through a clearance between the respective piston and cylinder. By this means the recuperation flow to each cylinder may be free from damping. In this damper the cylinders and pistons may be tapered towards their extremities. The minimum current may be adjusted by variable resistors R<SP>3</SP>, R<SP>4</SP>, and the maximum current by a variable resistance R<SP>5</SP>. The device 36 may be in the form of a telescopic device (Fig. 7, not shown), connected between the axle and chassis of the vehicle. The lever 90 is then dispensed with, and the magnification is obtained hydraulically by an arrangement of differential piston areas. The cylinder of the dashpot is afforded by a bore within the inertia mass 41. Where a permanent magnet is employed for providing the magnetic field, it may be combined with the mass 41. A telescopic shock-absorber is described (Fig. 3, not shown) in which a solenoid is carried by the piston and controls flow of liquid through a clearance between the piston and cylinder. In another construction (Fig. 1, not shown), reciprocating movement of a rod is damped by the resistance to the movement of an iron, steel or non-magnetic annular member, rigid with the rod and disposed in an annular chamber containing magnetizable liquid. A solenoid surrounds the outer wall of the chamber, which is of brass, but has iron inserts positioned so that the field is directed through the liquid. The annular member may be formed with slots or holes in order to vary the damping effect.