Patent ID: 8550427

Claim:
A normally-open solenoid valve comprising: a solenoid coil to produce a magnetic field when energized; a yoke of magnetic material encasing the solenoid coil; an armature of magnetic material surrounded by the yoke, and arranged to move in an axial direction of the solenoid coil when the solenoid coil is energized; a plunger of nonmagnetic nonmagnetic material arranged to move with movement of the armature; a valve seat member including a seat portion formed with a fluid passage to be closed and opened by a forward end portion of the plunger moving toward and away from the seat portion; and a coil spring disposed between a spring receiving portion of the plunger and the valve seat member, around the plunger, and arranged to urge the plunger in a direction toward the armature; the plunger including a flat portion which extends in a radial direction of the plunger at a position between the forward end portion of the plunger and the spring receiving portion, which faces to the seat portion, and which has an outer circumference so sized that an outside diameter of the flat portion is smaller than an inside diameter of the coil spring; wherein the forward end portion of the plunger includes a hemispherical end, the flat portion of the plunger is formed continuously between a larger diameter portion of the forward end portion and an outside circumferential surface of the plunger, the flat portion extends from an inner corner which is formed between the flat portion and the larger diameter portion, to an outer corner which is formed between the flat portion and the outside circumferential surface, and the inner and outer corners are formed so that a radius of curvature of the inner corner is smaller than or equal to R0.03 or a radius of curvature of the outer corner is smaller than or equal to R0.1.