Abstract: A wide variety of machines have moveable members that are operated by an hydraulic actuator. For example, an internal combustion engine has a camshaft which is mechanically coupled to rotate with the crankshaft and which opens and closes cylinder intake and exhaust valves. Traditionally the camshaft timing was fixed at a setting that produced the best operation for all engine operating conditions. However, it has been recognized that engine performance can be improved if the valve timing varies as a function of engine speed, engine load, and other factors. Thus a hydraulic actuator is being used on some engines to vary the coupling relationship of the camshaft to the crankshaft. A solenoid operated valve controls the application of pressurized fluid to operate the hydraulic actuator.

Abstract: An hydraulic valve has a body with a longitudinal bore therein. An annular recess is formed within the longitudinal bore and has a circumferential surface through which a fluid port opens. A filter band, with a plurality of apertures there through, is located within the annular recess abutting the circumferential surface. A helical spring has spaced apart convolutions that engage the filter band and exert an outward radial force which holds the filter band against the circumferential surface of the bore recess. A valve element, such as a spool, is slideably received within the longitudinal bore to control flow of fluid through the fluid port.