Patent ID: 6902038

Claim:
An engine oil drain plug comprising: a cylindrical bolt member having, on one end side thereof, a screw axis portion with a male screw formed thereon to be fixedly threaded into an oil drain hole provided on an oil pan of an engine, a secured portion adjacent to the one end side, and a distal end provided on a plane substantially same as an inner wall surface of the oil pan when the engine oil drain plug is fixedly threaded into the oil drain hole; a head portion formed on the other end side, said head portion being located outside the oil pan; an axial oil drain passage penetrating from the screw axis portion on the one end side to the head portion on the other end side to drain oil and having a first diameter portion at the one end side and a second diameter portion at the other end side with a diameter greater than that of the first diameter portion; and an annular valve seat provided adjacent to the head portion in the oil drain passage and having a slant surface at an end portion thereof toward the one end side of the cylindrical bolt member with an inner diameter increasing toward the one end side of the cylindrical bolt member, a movable valve body member disposed entirely inside the oil drain passage of the cylindrical bolt member, and having a valve body portion for engaging the slant surface of the valve seat to close the oil drain passage; and a cylindrical portion slidably disposed in and supported by the first diameter portion of the oil drain passage, said cylindrical portion having an opening at an upper end, a plurality of through-holes at a lower side, and an oil path therein communicating with the opening and the through-holes so that when the valve body portion is displaced from the slant surface of the valve seat toward the inside of the oil pan, the oil can flow outwardly through the drain passage and the oil path, and a spring member interposed between the secured portion adjacent to the one end side of the cylindrical bolt member and the cylindrical portion of the movable valve body member for biasing the movable valve body member to be engaged with the slant surface of the valve seat, wherein when said movable valve body member is pushed toward the oil pan, the movable valve body member biased by the spring member to a normally closed position allows the valve body portion to be displaced from the slant surface of the valve seat, thereby opening the drain passage and the oil path.