Edgeless valve spool design with variable clearance

A valve spool comprising:

• a cylindrical spool body having a spool longitudinal axis, a first spool body end wall and a second spool body end wall disposed axially opposite the first spool body end wall;
• and
• a spool outer surface comprising
• a first spool guide region proximate the first spool body end wall and having a first spool guide region outer surface,
• a second spool guide region proximate the second spool body end wall and having a second spool guide region outer surface, wherein the first spool guide region outer surface and the second spool guide region outer surface have a maximum spool guide region outer diameter that is equal, and
• a spool tight clearance region disposed between the first spool guide region and the second spool guide region and having a maximum spool tight clearance region outer diameter that is greater than the maximum spool guide region outer diameter,
• wherein the valve spool is installed in a spool valve assembly having a valve body with a valve bore having the valve spool disposed therein and having a valve bore inner diameter that is greater than the maximum spool tight clearance region outer diameter, and
• wherein the first spool guide region, the second spool guide region and the spool tight clearance region are dimensioned so that a first spool edge of the first spool guide region proximate the first spool body end wall and a second spool edge of the second spool guide region proximate the second spool body end wall can contact the valve bore and the spool tight clearance region does not contact the valve bore when the valve spool rotates about an axis that is perpendicular to the spool longitudinal axis.

A spool valve assembly comprising:

• a valve body having a valve bore extending longitudinally within the valve body and having a valve bore inner diameter, a high pressure fluid supply passage intersecting the valve bore, a high pressure fluid outlet passage intersecting the valve bore and a low pressure fluid drain passage intersecting the valve bore;
• and
• a valve spool disposed within the valve bore and having a cylindrical spool body, a spool longitudinal axis, a spool outer surface, a first spool body end wall and a second spool body end wall disposed axially opposite the first spool body end wall, wherein the spool outer surface comprises
• a first spool guide region proximate the first spool body end wall and having a first spool guide region outer surface with a maximum spool guide region outer diameter that is less than the valve bore inner diameter;
• a second spool guide region proximate the second spool body end wall and having a second spool guide region outer surface with the maximum spool guide region outer diameter of the first spool guide region outer surface;
• and
• a spool tight clearance region disposed between the first spool guide region and the second spool guide region and having a spool tight clearance region outer surface with a maximum spool tight clearance region outer diameter that is less than the valve bore inner diameter and greater than the maximum spool guide region outer diameter, wherein the high pressure fluid outlet passage is in fluid communication with the low pressure fluid drain passage and the high pressure fluid supply passage is not in fluid communication with the high pressure fluid outlet passage when the valve spool is in a first valve spool position within the valve bore, and the high pressure fluid supply passage is in fluid communication with the high pressure fluid outlet passage and the high pressure fluid outlet passage is not in fluid communication with the low pressure fluid drain passage when the valve spool is in a second valve spool position within the valve bore,
• wherein a minimum spool tight clearance region diametrical clearance between the spool tight clearance region of the spool outer surface and the valve bore is determined by a formula as follows:
• C
• T
• ⁢
• ⁢
• min
• =
• C
• Gmax
• *
• [
• L
• T
• L
• G
• +
• 2
• *
• L
• OFF
• L
• G
• ]
• where CTmin is the minimum spool tight clearance region diametrical clearance equal to the valve bore inner diameter minus the maximum spool tight clearance region outer diameter, CGmax is a maximum spool guide region diametrical clearance equal to the valve bore inner diameter minus the maximum spool guide region outer diameter, LG is a spool longitudinal guide length from the first spool body end wall to the second spool body end wall, LT is a spool longitudinal tight clearance region length, and LOFF is an offset length from a spool longitudinal tight clearance region midpoint to a spool longitudinal guide midpoint.

A spool valve assembly comprising:

• a valve body having a valve bore extending longitudinally within the valve body and having a valve bore inner diameter, a high pressure fluid supply passage intersecting the valve bore, a high pressure fluid outlet passage intersecting the valve bore and a low pressure fluid drain passage intersecting the valve bore;
• and
• a valve spool disposed within the valve bore and having a cylindrical spool body, a spool longitudinal axis, a spool outer surface, a first spool body end wall and a second spool body end wall disposed axially opposite the first spool body end wall, wherein the spool outer surface comprises
• a first spool guide region proximate the first spool body end wall and having a first spool guide region outer surface with a maximum spool guide region outer diameter that is less than the valve bore inner diameter;
• a second spool guide region proximate the second spool body end wall and having a second spool guide region outer surface with the maximum spool guide region outer diameter of the first spool guide region outer surface;
• and
• a spool tight clearance region disposed between the first spool guide region and the second spool guide region and having a spool tight clearance region outer surface with a maximum spool tight clearance region outer diameter that is less than the valve bore inner diameter and greater than the maximum spool guide region outer diameter, wherein the high pressure fluid outlet passage is in fluid communication with the low pressure fluid drain passage and the high pressure fluid supply passage is not in fluid communication with the high pressure fluid outlet passage when the valve spool is in a first valve spool position within the valve bore, and the high pressure fluid supply passage is in fluid communication with the high pressure fluid outlet passage and the high pressure fluid outlet passage is not in fluid communication with the low pressure fluid drain passage when the valve spool is in a second valve spool position within the valve bore,
• wherein the first spool guide region, the second spool guide region and the spool tight clearance region are dimensioned so that a first spool edge of the first spool guide region proximate the first spool body end wall and a second spool edge of the second spool guide region proximate the second spool body end wall can contact the valve bore and the spool tight clearance region does not contact the valve bore when the valve spool rotates about an axis that is perpendicular to the spool longitudinal axis.