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.