Patent ID: 7412989

Claim:
A solenoid valve of the normally closed type comprising: a solenoid section having a plunger axially attracted in dependence on electric current applied to a coil; a sleeve joined with the solenoid section and having a valve hole formed on the same axis as the plunger; a spool valve slidably fitted in the valve hole and urged to be brought into contact with the plunger by the resilient force of a spring retained in a spring chamber formed at a portion opposite the solenoid section, the spool valve being movable together with the plunger for controlling flow path areas of a supply port, an output port and a main drain port which open to the valve hole; a valve body having an insertion bore which is formed to pass therethrough and in which the sleeve is fitted to extend its axis approximately horizontally; a feedback port opening to the valve hole to be next to the spring chamber for leading a controlled pressure output from the output port, to a feedback land portion which is formed on the spool valve to have an area difference; wherein when the plunger is axially attracted to move the spool valve upon energization of the coil, the area of a flow path from the supply port to the output port is gradually increased as the area of a flow path from the output port to the main drain port is gradually decreased, and wherein the solenoid valve further comprises: an annular oil groove formed between the feedback port and an open end on the spring chamber side of the insertion bore of the valve body and at a portion corresponding to the spring chamber on the external surface of the sleeve; a drain passage formed on the external surface of an upper part of the sleeve to extend from the annular oil groove to an end of the sleeve for making an upper part of the annular oil groove communicate with the outside of the insertion bore; and a respiration passage extending through a lower part of the sleeve opposite the drain passage and connecting a lower part of the annular oil groove with a lower part of the spring chamber for making the annular oil groove communicate with the spring chamber, whereby an oil reserve is formed below the height of the drain passage.