The crankshaft is the most important part of the engine. It carries the force from the connecting rod and converts it into torque that is output through the crankshaft and drives other accessories on the engine. The crankshaft is subjected to the combined effect of centrifugal force of rotating mass, periodically changing gas inertia force and reciprocating inertia force, which makes the crankshaft subjected to bending and torsional load. Therefore, the crankshaft is required to have sufficient strength and stiffness, and the journal surface needs to be wear-resistant, work evenly and have good balance.