Electromagnetic actuator performing quick response

Abstract

An electromagnetic actuator includes a cylindrical coil, a stator core disposed in the cylindrical coil, a plate attached to one axial end of the stator core and an armature positioned to face the other axial end of the stator core. Upon energizing the coil, the armature is attracted to the stator core against a biasing force of a spring disposed in an inner space of the stator core. A depressed portion is formed on the plate and/or the stator core to suppress a magnetic flux passing therethrough and to reduce an amount of leakage flux. The magnetic flux generated by the coil is effectively used to drive the armature, and thereby a response time of the actuator is shortened. In other words, the armature is quickly driven upon energizing the coil.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an entire structure of a fuel injection system having an accumulator for accumulating pressurized fuel;

FIG. 2 is a cross-sectional view showing a depressurizing valve used in the injection system as a first embodiment of the present invention;

FIG. 3 is a cross-sectional view showing components of the depressurizing valve before being assembled to an accumulator;

FIG. 4 is a cross-sectional view showing the depressurizing valve connected to the accumulator;

FIG. 5 is a graph showing a response time of the depressurizing valve in relation to a diameter of a depressed portion formed in a plate used in a coil unit; and

FIG. 6 is a cross-sectional view showing a depressurizing valve used in the injection system as a second embodiment of the present invention.

Claims

1. An electromagnetic actuator comprising: a cylindrical coil generating a magnetic field by supplying electric current thereto;a stator core disposed in a cylindrical coil;a plate positioned at one axial end of the cylindrical coil and the stator core; andan armature positioned at another axial end of the cylindrical coil and the stator core, the armature forming a magnetic circuit together with the stator core and the plate, the armature being attracted toward the stator core upon generation of the magnetic field, wherein:the stator core includes a depressed portion for suppressing an amount of magnetic flux flowing therethrough, the depressed portion being formed on one axial end of the stator core facing the plate.

2. An electromagnetic actuator comprising: a cylindrical coil generating a magnetic field by supplying electric current thereto;a stator core disposed in a cylindrical coil;a plate positioned at one axial end of the cylindrical coil and the stator core; andan armature positioned at another axial end of the cylindrical coil and the stator core, the armature forming a magnetic circuit together with the stator core and the plate, the armature being attracted toward the stator core upon generation of the magnetic field, wherein:the plate includes a depressed portion for suppressing an amount of magnetic flux flowing therethrough, the depressed portion being formed on one surface of the plate facing the stator core.

3. The electromagnetic actuator as in claim 2, wherein: the armature core includes another depressed portion for suppressing an amount of magnetic flux flowing therethrough, the other depressed portion being formed on one axial end of the stator core facing the plate.

4. The electromagnetic actuator as in claim 2, wherein: the plate further includes another depressed portion for suppressing an amount of magnetic flux flowing therethrough, the another depressed portion being formed on the other surface of the plate symmetrically to the depressed portion formed on the one surface.

5. The electromagnetic actuator as in claim 2, wherein: the depressed portion is formed in the plate to pass through an entire thickness of the plate.

6. The electromagnetic actuator as in claim 1, wherein: a depth of the depressed portion is larger than an air gap between the armature and the stator core which is formed when the armature is attracted to the stator core.

7. The electromagnetic actuator as in claim 2, wherein: a depth of the depressed portion is larger than an air gap between the armature and the stator core which is formed when the armature is attracted to the stator core.

8. The electromagnetic actuator as in claim 1, wherein: the armature is biased in a direction away from the stator core by a biasing spring disposed in an inner space formed in the stator core; anda diameter of the depressed portion is in a range from 0.6·di2 to 0.9·Di2, where di2 is an inner diameter of the inner space formed in the stator core and Di2 is an outer diameter of the stator core.

9. The electromagnetic actuator as in claim 2, wherein: the armature is biased in a direction away from the stator core by a biasing spring disposed in an inner space formed in the stator core; anda diameter of the depressed portion is in a range from 0.6·di2 to 0.9·Di2, where di2 is an inner diameter of the inner space formed in the stator core and Di2 is an outer diameter of the stator core.

10. An electromagnetic actuator comprising: a cylindrical coil generating a magnetic field by supplying electric current thereto;a stator core having a cylindrical portion and a flange connected to one axial end of the cylindrical portion, the flange having a diameter larger than that of the cylindrical portion, the cylindrical portion being disposed in the cylindrical coil, the flange being positioned to face one axial end of the cylindrical coil; andan armature positioned at another axial end of the cylindrical coil and the stator core, the armature forming a magnetic circuit together with the stator core, the armature being attracted toward the stator core upon generation of the magnetic field, wherein:the flange includes a depressed portion for suppressing an amount of magnetic flux flowing therethrough, the depressed portion being formed at a center portion of the flange.