Solenoid device with stable activation

1. A solenoid comprising:

a core having a junction surface;

a plunger having a junction surface and located proximate to the core;

a shading ring located proximate to an interface between the core junction surface and the plunger junction surface, the shading ring having an outside diameter slightly smaller than the diameter of the core, and operable to produce a concentration of magnetic attraction within an annular range of the interface between a center of the interface and a location of the shading ring;

wherein one of the core junction surface or the plunger junction surface is substantially flat and the other of the core junction surface or the plunger junction surface has a concavity formed therein such that an annular contact region is formed at the interface between the core junction surface and the plunger junction surface which is substantially smaller than the respective junction surfaces and is located proximate to the annular range of the concentration of magnetic attraction.

2. The solenoid of claim 1 wherein the contact region is arranged so as to conform substantially to the annular range of the concentration of magnetic attraction.

3. The solenoid of claim 1 wherein the concavity is conical and the junction surface having the concavity formed therein optionally further comprises a relief along a periphery of the junction surface.

4. The solenoid of claim 1 wherein the plunger junction surface is substantially flat and the core junction surface has at least one of:

a) a concave shape with a relief at a center thereof; and

b) a relief along a periphery thereof.

5. The solenoid of claim 2 wherein the contact region between the respective junction surfaces is located over an annular region of the interface between the respective junction surfaces, wherein the annular contact region has a center radius slightly smaller than a radial position of an inner diameter of the shading ring.

6. The solenoid of claim 1 wherein the shading ring is embedded within the core.

7. The solenoid of claim 1 wherein the shading ring is embedded within the plunger.

8. The solenoid of claim 1 wherein the shading ring is embedded at least partially within the core and at least partially within the plunger.

9. The solenoid of claim 1 comprising two shading rings, the first shading ring being disposed in the core and the second shading ring being disposed in the plunger.

10. A solenoid comprising:

a core assembly fixed within the solenoid and having a junction surface;

a plunger moveable within the solenoid and having a junction surface;

a shading ring located proximate to an interface between the core assembly junction surface and the plunger junction surface, the shading ring having an outside diameter slightly smaller than the diameter of the core and operable to produce a concentration of magnetic attraction at the interface between the plunger junction surface and the core assembly junction surface within an annular range of the interface between a center of the interface and a radial position of an inner diameter of the shading ring;

wherein one of the core junction surface or the plunger junction surface is substantially flat and substantially perpendicular to an adjoining side surface thereof and the other of the core junction surface or the plunger junction surface has a conical concavity formed therein such that when the respective junction surfaces are contacted, an annular contact region is formed at the interface such that the contact region between the plunger junction surface and the core assembly junction surface is substantially smaller than the respective junction surfaces and located proximate to the annular range of the concentration of magnetic attraction.

11. The solenoid of claim 10 wherein the shading ring is embedded within the plunger.

12. The solenoid of claim 10 wherein the shading ring is embedded within the core.

13. The solenoid of claim 10 wherein the core assembly comprises substantially only a core and the core assembly junction surface is a core junction surface.