The present invention is directed to the field of hydraulic dampers for reducing undesired pressure surges or oscillations in systems requiring hydraulic damping. This invention has particular applicability to the damping of periodically varying motions in systems which result in noise or oscillation in hydraulic pressure.
In a particular example, undesirable oscillation in a hydraulic system occurs in the nose wheel assembly of an aircraft, which is typically steered using a hydraulic system. The pivot point of the wheel is typically located at a point ahead of the wheel axle, rather like a caster. The mass of wheel is behind the pivot, and the dynamics of the system are such that the wheel tends to "shimmy" while moving along the ground, in a manner similar to other commonly-observed caster-type wheels, e.g. the wheels on a shopping cart.
Such wheel shimmy results in wear and tear on the wheel and supporting strut which may increase exponentially resulting structural damage to the aircraft. Suppression of shimmy often requires compromises in steering control accuracy. It is desirable to provide a hydraulic means of damping which does not compromise steering accuracy.
One known hydraulic damper uses a piston and a pair of springs to form a compliance, and a hydraulic orifice to form a damping control which reduces rapid shimmy motion while permitting the relatively slow motion of steering. However, such dampers include a number of mechanical elements.
Hydraulic systems are prone to pressure surges which occur when large valves are quickly opened or closed. This phenomenon, also known as "water hammer," is also observed in common household plumbing when faucets are abruptly turned off, producing a sound and a shock to the pipes. Such surges also create additional wear and tear in hydraulic systems, thereby shortening the operational life of the respective components.