Solenoid valve, solenoid and hydraulic power system

A solenoid comprising:

• a solenoid housing including a longer outer cylindrical wall and a shorter inner cylindrical wall between which a coil receiving cylindrical space is defined, the solenoid housing having a head portion at one axial end thereof and an opened base portion at another axial end thereof, the inner cylindrical wall being formed at an inner surface thereof with an annular recess leaving a cylindrical wall that serves as a rear core;
• an annular coil disposed in the coil receiving cylindrical space, the annular coil including a cylindrical inner surface and a cylindrical outer surface that extend in parallel with an axis of the annular coil;
• a front core disposed in the opened base portion of the solenoid housing and having a smaller diameter portion projected into the inner cylindrical wall of the solenoid housing, the front core being formed at the smaller diameter portion thereof with an axially extending through bore;
• a sleeve including a smaller diameter portion tightly received in the annular recess of the inner cylindrical wall of the solenoid housing, a larger diameter portion put between the cylindrical inner surface of the annular coil and a cylindrical outer surface of the smaller diameter portion of the front core and a sloped annular intermediate portion that extends between the smaller and larger diameter portions of the sleeve;
• a plunger axially slidably received in the axially extending through bore of the front core, the plunger having a first portion projected into the smaller diameter portion of the sleeve and a second portion projected outward;
• an armature secured to the first portion of the plunger to move together therewith;
• and
• a spring biasing the plunger toward an outside of the solenoid housing,
• wherein the solenoid housing, the front core and the rear core are made of a magnetic material,
• wherein the sleeve is made of a non-magnetic material,
• wherein the front core has both an armature receiving recess in the smaller diameter portion thereof to receive therein one end of the armature and a tapered outer surface that surrounds the armature receiving recess, the diameter of the tapered outer surface increasing as a distance from the head portion of the solenoid housing increases,
• wherein the rear core is placed between the head portion of the solenoid housing and the front core, the armature forms a magnetic path for a magnetic field in cooperation with cylindrical walls of the solenoid housing the front core and the rear core, and
• wherein a first seal member is operatively disposed between the smaller diameter portion of the front core and the larger diameter portion of the sleeve and a second seal member is operatively disposed between the rear core and the smaller diameter portion of the sleeve.

A hydraulic power system used in a steering power steering system for a motor vehicle, comprising:

• a variable capacity pump for feeding a power cylinder with a pressurized hydraulic fluid to assist a steering work applied to a steering wheel, the variable capacity pump including a pump housing, a drive shaft rotatably held in the pump housing, a cam ring movably received in a pump element receiving recess formed in the pump housing, a rotor arranged in the cam ring and driven by the drive shaft, vanes axially movably held by the rotor while causing tops of the vanes to slidably contact with an inner surface of the cam ring, and
• a solenoid valve that controls an eccentricity of the cam ring, the solenoid valve including:
• a solenoid housing including a longer outer cylindrical wall and a shorter inner cylindrical wall between which a coil receiving cylindrical space is defined, the solenoid housing having a head portion at one axial end thereof and an opened base portion at the other axial end thereof, the inner cylindrical wall being formed at an inner surface thereof with an annular recess leaving a cylindrical wall that serves as a rear core;
• an annular coil disposed in the coil receiving cylindrical space, the annular coil including a cylindrical inner surface and a cylindrical outer surface that extend in parallel with an axis of the annular coil;
• a front core disposed in the opened base portion of the solenoid housing, the front core having a smaller diameter portion projected into the inner cylindrical wall of the solenoid housing, the front core being formed at the smaller diameter portion thereof with an axially extending through bore;
• a sleeve including a smaller diameter portion tightly received in the annular recess of the inner cylindrical wall of the solenoid housing, a larger diameter portion put between the cylindrical inner surface of the annular coil and a cylindrical outer surface of the smaller diameter portion of the front core and a sloped annular intermediate portion that extends between the smaller and larger diameter portions of the sleeve;
• a plunger axially slidably received in the axially extending through bore of the front core, the plunger having a first portion projected into the smaller diameter portion of the sleeve and a second portion projected outward;
• an armature secured to the first portion of the plunger to move together therewith;
• a spring biasing the plunger toward an outside of the solenoid housing;
• and
• a valve unit actuated by the second portion of the plunger, the valve unit including a valve housing connected to an outside of the front core, a spool slidably received in the valve housing and having an end that is in contact with the second portion of the plunger, and a spring for biasing the spool toward the second portion of the plunger,
• wherein the solenoid housing, the front core and the rear core are made of a magnetic material,
• wherein the sleeve is made of a non-magnetic material,
• wherein the front core has both an armature receiving recess in the smaller diameter portion thereof to receive therein one end of the armature and a tapered outer surface that surrounds the armature receiving recess, a diameter of the tapered outer surface increasing as a distance from the head portion of the solenoid housing increases,
• wherein the rear core is placed between the head portion of the solenoid housing and the front core,
• wherein the armature forms a magnetic path for a magnetic field in cooperation with the cylindrical portion of the solenoid housing, the front core and the rear core,
• wherein the valve housing of the valve unit has an axially extending spool receiving bore portion and an oil passage exposed to the spool receiving bore portion and communicating the axially extending through bore of the front core, and
• wherein a first seal member is operatively disposed between the smaller diameter portion of the front core and the larger diameter portion of the sleeve, and a second seal member is operatively disposed between the rear core and the smaller diameter portion of the sleeve.