Solenoid operated hydraulic control valve

A spool valve comprising:

• a valve spool including a central recess region of predetermined length and substantially constant cross section along said region length;
• a valve body having a cylindrical cavity in a spool valve housing and slidably fitted over said valve spool, including a supply port, a discharge port separated from said recess region length, said supply port and said discharge port having substantially identical areas along said valve body;
• means for biasing said valve spool to a normally closed position with said valve spool recess region positioned beyond said supply port toward said discharge port to block fluid flow through said valve recess region from said supply port, wherein said means for biasing includes a compression type spring penetrating said valve body from a spring end of said valve body, said spring being axially aligned with said valve spool;
• means for displacing said valve spool to an open position with said valve spool recess region displaced midway between said supply port and said discharge port to allow flow through said valve recess region from said supply port to said discharge port without flow induced valve spool force imbalance, wherein said means for displacing includes a plunger pin penetrating said valve body from a plunger pin end of said valve body opposite said valve body spring end;
• a valve body plunger end wall for retaining said valve spool in said normally closed position;
• wherein said supply port includes an annular supply channel in said valve body surrounding said valve spool, and said discharge port includes an annular discharge channel in said valve body surrounding said valve spool, said supply channel and said discharge channel having substantially equal lengths along said valve body;
• and
• wherein said plunger pin penetrates said valve body plunger end wall.

A solenoid operated spool valve comprising:

• a valve spool having a spool axis including a central recess region of predetermined length and substantially constant cross section along said recess region length;
• a valve body slidably fitted over said valve spool, including a supply port, a discharge port separated from said supply port by a port separation length less than said recess region length, said supply port and said discharge port having substantially identical areas along said valve body;
• a compression type spring, axially aligned with said valve spool axis, penetrating said valve body from a spring end of said valve body, for biasing said valve spool to a normally closed position, with said valve spool recess region positioned beyond said supply port toward said discharge port to block fluid flow through said valve recess region from said supply port;
• a plunger pin, penetrating said valve body from a plunger pin end of said valve body opposite said valve body spring end, and having a plunger pin end of said valve for displacing said valve spool to an open position, with said valve spool recess region displaced midway between said supply port and said discharge port to allow flow through said valve recess region from said supply port to said discharge port without flow induced valve spool force imbalance;
• a solenoid stator, including a central pole piece with a linear bearing through it for slidably retaining said plunger pin along said valve spool axis, and an annular pole piece, axially aligned with said central pole piece, and having a diameter substantially greater than said central pole piece;
• a solenoid armature, coupled to said plunger pin through said stator central pole piece bearing, having an axis aligned with said plunger pin axis, a working gap surface substantially parallel to the surface of said central pole piece, and a circumferential non-working gap surface substantially parallel to the surface of said stator annular pole piece;
• and
• a solenoid coil, wound around said central pole piece, for operating said armature coupled plunger, pin with an electric signal.