Drain plug structure for oil pan

An oil pan for an internal combustion engine, comprising:

• a detachable drain plug structure for closing off a drain hole disposed in a bottom portion of the oil pan, the detachable drain plug structure including:
• a columnar stopper portion inserted into the drain hole and rotated to prevent withdrawal;
• a sealing member fitted to an outer periphery of the columnar stopper portion;
• an operating portion for a rotation operation disposed on an outside exposed end portion of the columnar stopper portion;
• a plurality of cantilevered arcuate arm portions projecting radially outwards from the outside exposed end portion of the columnar stopper portion and arranged in series along a circumferential direction;
• a loosening-prevention meshing portion disposed on both a tip end portion of each arcuate arm portion and an opening edge portion of the drain hole, and demonstrates a loosening-prevention function by fitting together in a recess/projection engagement;
• and
• a seating flange portion provided as a single piece with one end portion of the columnar stopper portion and projecting radially therefrom, the seating flange portion is larger in diameter than said one end portion and has a top portion of predetermined thickness;
• wherein the seating flange portion has a shape that is equally divided via four slot grooves having a roughly deformed “<” shape such as to leave bridge portions at four locations in the circumferential direction, and said seating flange portion is slotted in a radial direction and the circumferential direction to form the plurality of cantilevered arcuate arm portions into four arcuate arm portions that are cantilevered and have a circular arc shape, arranged in series along the circumferential direction, and the four bridge portions remain as a root portion;
• wherein the circumferential length of the four arcuate arm portions is sufficiently large to provide adequate flexibility in a thickness direction with the bridge portions as a support point, and the structure enables elastic deformation based on the elastic strength thereof in the thickness direction;
• wherein a peripheral length and a wall thickness of the four arcuate arm portions are set to take account of the torque required when the drain plug is removed and the amount of flexing and deformation of the four arcuate arm portions required to engage/disengage the recess/projection engagement, so the operations do not lead to damage and repeated usage is possible;
• and
• wherein the four arcuate arm portions include engaging projections respectively disposed at a tip end portion on a rear surface of the four arcuate arm portions, and wherein the engaging projections each comprise a flat top portion parallel to the rear surface, a first inclined surface extending from the flat top portion towards the root portion defined by the four bridge portions, and a second inclined surface disposed between the flat top portion and a tip end surface of the corresponding one of the four arcuate arm portions.

An internal combustion engine, comprising:

• an oil pan provided at a lower portion thereof, the oil pan including a detachable drain plug structure for closing off a drain hole disposed in a bottom portion of the oil pain, the detachable drain plug structure including:
• a columnar stopper portion inserted into the drain hole and rotated to prevent withdrawal;
• a sealing member fitted to an outer periphery of the columnar stopper portion;
• an operating portion for a rotation operation disposed on an outside exposed end portion of the columnar stopper portion;
• a plurality of cantilevered arcuate arm portions projecting radially outwards from the outside exposed end portion of the columnar stopper portion and arranged in series along a circumferential direction;
• a loosening-prevention meshing portion disposed on both a tip end portion of each arcuate arm portion and an opening edge portion of the drain hole, and demonstrates a loosening-prevention function by fitting together in a recess/projection engagement;
• and
• a seating flange portion provided as a single piece with one end portion of the columnar stopper portion and projecting radially therefrom, the seating flange portion is larger in diameter than said one end portion and has a top portion of predetermined thickness;
• wherein the seating flange portion has a shape that is equally divided via four slot grooves having a roughly deformed “<” shape such as to leave bridge portions at four locations in the circumferential direction, and said seating flange portion is slotted in a radial direction and the circumferential direction to form the plurality of cantilevered arcuate arm portions into four arcuate arm portions that are cantilevered and have a circular arc shape, arranged in series along the circumferential direction, and the four bridge portions remain as a root portion;
• wherein the circumferential length of the four arcuate arm portions is sufficiently large to provide adequate flexibility in a thickness direction with the four bridge portions as a support point, and the structure enables elastic deformation based on the elastic strength thereof in the thickness direction;
• wherein a peripheral length and a wall thickness of the four arcuate arm portions are set to take account of the torque required when the drain plug is removed and the amount of flexing and deformation of the four arcuate arm portions required to engage/disengage the recess/projection engagement, so the operations do not lead to damage and repeated usage is possible;
• wherein the bottom portion of the oil pan has an annular seat portion that includes four engaging recesses for engaging with the four arcuate arm portions, wherein the four engaging recesses each comprise a flat bottom surface parallel to an upper surface of the annular seat portion, and a first inclined surface and a second inclined surface having a different inclination from one another.