Solenoid valve for brake system

1. A solenoid valve for a brake system, the solenoid valve comprising:

a magnet core that is provided in a cylindrical shape, is installed in a bore of a modulator block, and has a through-hole opening in a lengthwise direction thereof and a radial direction passage communicating with the through-hole; an armature that is installed at one end of the magnet core so as to be reciprocated; a valve seat that is provided at the other end of the magnet core and has an orifice; a plunger that is inserted into the through-hole and performs a sliding motion by the armature to open and close the orifice; a sleeve that is fixed to the bore while accommodating the armature and the magnet core; and a return spring that is provided to apply an elastic restorative force to the plunger to open the orifice,

wherein a passage hole is provided in a spiral shape along the through-hole at an inner circumferential surface of the magnet core to discharge air between the magnet core and the plunger and air between the magnet core and the armature.

2. The solenoid valve of claim 1 , wherein the passage hole is molded in a form rolling.

3. The solenoid valve of claim 1 , wherein:

the magnet core is provided at an inner circumferential surface thereof with a spring support ledge protruding to support a lower end of the return spring;

the plunger is provided with an outer circumferential surface thereof with a step portion stepped inward to support an upper end of the return spring; and

one end of the passage hole extends to a portion between the magnet core and the armature, and the other end of the passage hole extends to a portion between the spring support ledge and the step portion, to expand a gap between the magnet core and the armature and a gap between the magnet core and the plunger.

4. The solenoid valve of claim 3 , wherein the passage hole connects to the orifice through a transfer passage hole formed lengthwise along the spring support ledge.