Power plants – Pressure fluid source and motor – Condition responsive control of motive fluid flow
Reexamination Certificate
2005-01-04
2005-01-04
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Condition responsive control of motive fluid flow
C137S118060, C137S114000
Reexamination Certificate
active
06837047
ABSTRACT:
A hydraulic valve assembly, for use in a hydrostatic transmission, for controlling fluid transfer between a first, a second and a third line, wherein two of the lines define first and second pressure lines, within a closed-loop circuit. The valve assembly comprises: a valve body having ports in communication with the three lines; a spool bore; a valve spool, adapted for sealing reciprocation within the spool bore, having a first and second end portion, a connecting portion, and a first and second bypass orifice within the valve spool; and dampers for centering the valve spool. This spool is movable from a neutral position occurring when the fluid pressure forces in the first and second pressure lines are substantially similar, to a first or a second position occurring when the fluid pressure force in the first pressure line is greater or less than that in the second pressure line, respectively. The bypass orifices are enabled in the neutral position, but are substantially disabled in the first and second positions. A hydraulic system utilizing the valve assembly and a method for increasing the width of the dead band of the hydrostatic transmission in a neutral mode of operation are also set forth.
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Dong Xingen
Whitaker James S.
Kershteyn Igor
Look Edward K.
Parker-Hannifin Corporation
Pophal Joseph J.
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