What is the engine crankshaft

Crankshaft is an important part of engine. It bears the force from the connecting rod and converts it into torque, which is output through the crankshaft and drives other accessories on the engine. The crankshaft is subjected to the combined action of centrifugal force of rotating mass, periodic gas inertia force and reciprocating inertia force, which makes the crankshaft bear the 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.
In order to reduce the mass of the crankshaft and the centrifugal force generated during its movement, the crankshaft journal is often made hollow. An oil hole is opened on the surface of each journal to introduce or lead out the oil to lubricate the surface of the journal. In order to reduce stress concentration, the joints of main journal, crank pin and crank arm are connected by transition arc.
The function of crankshaft balance weight (also known as counterweight) is to balance the rotating centrifugal force and its torque. Sometimes it can also balance the reciprocating inertia force and its torque. When these forces and moments balance themselves, the balance weight can also be used to reduce the load of the main bearing. The number, size and placement position of the balance weight shall be considered according to the number of cylinders of the engine, the arrangement of cylinders and the shape of the crankshaft. The balance weight is generally cast or forged with the crankshaft. The balance weight of high-power diesel engine is manufactured separately from the crankshaft and then connected with bolts.
The crankshaft is generally forged with medium carbon steel or medium carbon alloy steel. In order to improve the wear resistance and fatigue strength, the journal surface is subject to high-frequency quenching or nitriding treatment and fine grinding to meet the requirements of high surface hardness and surface roughness. It cooperates with the connecting rod to turn the gas pressure acting on the piston into rotating power and transmit it to the transmission mechanism of the chassis. At the same time, drive the valve distribution mechanism and other auxiliary devices, such as fan, water pump, generator, etc.
When working, the crankshaft bears the effects of gas pressure, inertia force and inertia moment. The force is large and complex, and bears the impact of alternating load. At the same time, the crankshaft is a high-speed rotating part. Therefore, the crankshaft is required to have sufficient stiffness and strength, good ability to bear impact load, wear resistance and good lubrication.