Patent ID: 8647075

Claim:
A fluid device comprising: a variable swashplate adapted for movement between a first position and a second position; a control piston adapted to selectively move the variable swashplate between the first and second positions; a control valve in fluid communication with the control piston, the control valve including: a sleeve defining a spool bore, at least one fluid inlet passage that is in fluid communication with a fluid source and at least one control fluid passage that is in fluid communication with the control piston, the control fluid passage having an opening at the spool bore, the opening having a first diameter; and a spool slidably disposed in the spool bore of the sleeve, the spool including a metering surface that selectively communicates fluid between the fluid inlet passage and the control fluid passage, the metering surface having a first end and an oppositely disposed second end, the metering surface having a generally cylindrical outer surface and a continuously tapered surface disposed between the first and second ends, the tapered surface meeting the generally cylindrical outer surface at a common edge, the tapered surface including an oblique angle that flares outwardly from the first end to the second end, wherein the degree of the angle is a function of at least one dimension of the opening, wherein the tapered surface has an axial length of not more than about 10 percent of the first diameter and the degree of the angle of the tapered surface is adapted to provide a linear flow area per axial displacement of the spool over a range of axial displacements equaling the axial length of the tapered surface.