Patent ID: 6422254
Filing Date: 2002-07-23
Classification: F16H,Y10T

Abstract:
A hydraulic neutral start control valve for a servo-controlled variable displacement hydraulic unit comprising:a valve housing having a spool bore therein and a signal pressure passage in fluid communication with the bore; a cylindrical valve spool mounted for sliding movement within the spool bore, the spool including opposite first and second ends, the second end of the spool having a predetermined radius and surface area; a plunger slidably mounted in the spool bore adjacent the second end of the spool, the plunger including a sealing surface thereon disposed in the bore and directed toward the second end of the spool, the sealing surface of the plunger extending radially outward beyond the radius of the second end to define an annular area in fluid communication with the signal pressure passage; a first positioning spring located between the valve housing and the first end of the spool so as mechanically urge the spool in a first direction axially; a second positioning spring located between the valve housing and the plunger so as to bias the sealing surface of the plunger into sealing contact with the second end of the spool and thereby mechanically urge the spool in a second direction opposite to the first direction in the absence of a threshold signal pressure; the plunger and the second end of the spool remaining in sealing contact with each other and the first and second positioning springs maintaining the valve in a closed or neutral position so long as a signal pressure input to the signal pressure passage and thereby to the annular area of the plunger is less than the threshold signal pressure; and the plunger separating from the spool and thereby allowing the signal pressure to hydraulically act on the second end of the spool to operate the valve when the signal pressure applied exceeds the threshold pressure.