The crankshaft is the most important component in an engine. It bears the force transmitted by the connecting rod and converts it into torque, which is output through the crankshaft and drives other accessories on the engine to work. The crankshaft is subjected to the combined action of centrifugal force from rotating mass, periodic gas inertia force, and reciprocating inertia force, which causes the crankshaft to bear bending and torsional loads. Therefore, it is required that the crankshaft has sufficient strength and stiffness, and the journal surface should be wear-resistant, work evenly, and have good balance.
Brief introduction
The most important component in an engine. It bears the force transmitted by the connecting rod and converts it into torque, which is output through the crankshaft and drives other accessories on the engine to work. The crankshaft is subjected to the combined action of centrifugal force from rotating mass, periodic gas inertia force, and reciprocating inertia force, which causes the crankshaft to bear bending and torsional loads. Therefore, it is required that the crankshaft has sufficient strength and stiffness, and the journal surface should be wear-resistant, work evenly, and have good balance.
To reduce the mass of the crankshaft and the centrifugal force generated during motion, the crankshaft journal is often made hollow. There are oil holes on each journal surface for introducing or extracting engine oil to lubricate the journal surface. To reduce stress concentration, transition arcs are used at the connection between the main journal, crank pin, and crank arm.
The function of crankshaft balance weight (also known as counterweight) is to balance the rotational centrifugal force and its torque, and sometimes it can also balance the reciprocating inertial force and its torque. When these forces and moments reach equilibrium, the balance weight can also be used to reduce the load on the main bearings. The number, size, and placement of balance weights should be considered based on factors such as the number of cylinders, cylinder arrangement, and crankshaft shape of the engine. The balance weight is generally cast or forged as a whole with the crankshaft. For high-power diesel engines, the balance weight is manufactured separately from the crankshaft and then connected together with bolts.
