Patent GB-714180-A (GB)
Title: Improvements in or relating to hydraulic dampers
IPC: F16F9/504
Filed: 1951-12-10
Abstract: 714,180. Hydraulic dampers. SHEPHERD, G. H. Dec. 10, 1951, No. 28838/51. Class 108(3) In a hydraulic damper for a vehicle suspension, a freelyacting spring-loaded by-pass valve l is actuated by inertia on acceleration of the unsprung mass so that a minimum restraint is offered to movement of this mass during the duration of the period of any impact thereon due to forward movement of the vehicle. A piston rod a has a concentric passage y which connects the space below a piston c (via a port x) with a reservoir R. A further piston t is slidable on the rod a against the action of a spring wand can - thus cut-off the port x. A plate B which is a sliding fit in the cylinder d has an integral sleeve E which is formed with ports F and is slidably mounted relative both to the rod a and to a head e between the cylinder d and reservoir R. The plate B is acted on by a spring D and a weaker spring C. The space between the plate B and the piston c is connected with the passage y by a small section duct G and a larger section port X, the entry to which is controlled by a piston valve I normally urged to a port-opening position by a spring J. Each end-face of the valve I is connected by a small-section duct K and a non-return ball-valve L permits flow from the space between the pistons t, c to the lower face of the valve I. A duct r in the lower end-wall of the cylinder d leads to the reservoir R but is normally closed to the interior of the cylinder d by the valve l which is urged by a spring n into engagement with an abutment ring m. An annular duct 0 in the valve I is connected by ports q with the interior of the cylinder d. , Operation: During the duration of an impact which results in a compression stroke, the valve l, due to its inertia, moves to connect the ducts 0 and r and liquid passes freely from below the piston t to the reservoir R.. Liquid is replenished through a ball-valve H. When the impact ceases the valve l moves back to cut off the duct rand damping of the momentum of the unsprung parts occurs by restriction to flow through the port x which is progressively cut-off by movement of the piston t on the piston rod a. During the compression stroke the plate B follows the piston c owing to the restriction to flow provided by the duct G. On rebound, flow from above the piston occurs freely through the space between the piston rod a and the inner wall of the head e until this space is cut-off by return therein of the sleeve E. This occurs when the piston again reaches its normal static-load position. The plate B takes up the same position relative to the head e whatever the static load due to the action of the spring D which overcomes the spring C and drives in the sleeve E until the port F is cut off. The port X permits a free flow from above the piston c to the reservoir, via the passage y, when the vehicle wheel drops into a pothole from the static position. On rebound, after a compression stroke, the port X is closed since during the compression stroke pressure acts through the one-way valve L on the underside of the piston valve I. On the rebound stroke, liquid is trapped between the valves I and L and escapes slowly through the duct K.