An improved rotary spool control system for a closed hydrostatic circuit and
method
to use the same. The control spool utilizes metering of the spool notches and specifically
the metering of the servo drain notch wherein the drain notch is of irregular cross
sectional shape. Because of the metering and irregular cross sectional shape, this
spool is able to provide an aggressive response while still having smooth linear
control. The method of creating the feedback control includes displacing pressurized
fluid through the hydrostatic circuit rotating the control spool to create an error
signal removing the error signal with a control sleeve and metering the servo piston
drain with the irregularly shaped metering porting notch.