The crankshaft is the most important component in the engine. It bears the force transmitted by the connecting rod and converts it into torque through the crankshaft output and drives other accessories on the engine to work. The crankshaft is affected by the centrifugal force of the rotating mass, the periodically changing gas inertial force and the reciprocating inertial force, so that the crankshaft is subjected to the bending torsional load. Therefore, the crankshaft is required to have sufficient strength and rigidity, and the surface of the journal needs to be wear-resistant, work evenly, and have good balance. In order to reduce the mass of the crankshaft and the centrifugal force generated during movement, the crankshaft journal is often made hollow. There are oil holes on the surface of each journal to introduce or extract oil to lubricate the surface of the journal. In order to reduce stress concentration, the joints of the main journal, the crank pin and the crank arm are all connected by transitional arcs.