Internal combustion engine with improved lubrication system

An internal combustion engine, wherein a pressure in an internal space including a crankcase chamber thereof pulsates owing to a reciprocating movement of a piston in a cylinder, the internal combustion engine comprising:

• an oil tank separated from the internal space and configured to store lubricating oil therein;
• a first passage communicating a vertically lower part of the internal space with a gas phase part of the oil tank;
• a first check valve provided in the first passage to permit a flow from the internal space to the oil tank but not in a reverse direction;
• a second passage connected with the gas phase part of the oil tank;
• an intake passage connecting the internal space with the second passage;
• a second check valve provided in the intake passage to permit a flow from the second passage to the internal space but not in a reverse direction;
• a third passage communicating a liquid phase part of the oil tank with the second passage;
• a third check valve provided in the third passage to permit a flow from the oil tank to the second passage but not in a reverse direction;
• and
• a flow regulator valve provided in a part of the third passage located between the third check valve and the second passage for regulating a flow of lubricating oil flowing through the third passage.