US Patent 7412989 Solenoid valve

In a solenoid valve 10, an annular oil groove 66 is formed at a portion corresponding to a spring chamber 56 on the external surface of a sleeve 19, a drain passage 68 is formed to make an upper part of the annular oil groove 66 communicate with the outside of an insertion bore 61, and a throttle hole 67 is provided at a lower part of the annular oil groove 66 for making the annular oil groove 66 communicate with the spring chamber 56. Since the annular oil groove 66 communicates with the outside of the insertion bore 61 at its upper part through the drain passage 68, it can be realized to store the operating oil to the height of the upper part of the annular oil groove 66, so that the operating oil can be reserved in the spring chamber 56 which communicates with the annular oil groove through the throttle hole 67. Further, the operating oil is supplied from a feedback port 48 next to the spring chamber 56 through a clearance between the spool valve 19 and a valve hole 18. Thus, the solenoid valve 10 is able to secure the damping effect of the working oil on the spool valve 19 and a plunger 17 and to suppress the self oscillation even while being operated in the atmosphere for a long time.