How the crankshaft works

The working principle of the crankshaft is to convert the force transmitted from the connecting rod into torque, drive other accessories of the engine to work, while bearing bending and torsional loads.

The crankshaft is one of the most important components in the engine, and its working principle mainly involves the conversion of force and energy transfer. The following is a detailed analysis of its working principle:

‌The conversion of force

The core function of the crankshaft is to convert the linear motion of the piston into a rotary motion. When the mixed gas in the engine is ignited, the piston moves reciprocatingly in the cylinder, and this force is transmitted to the crankshaft through the connecting rod. Through its unique structure, the crankshaft converts this reciprocating force into rotational torque, thereby driving the operation of other accessories of the engine.

‌Loads to bear

The crankshaft needs to withstand a variety of complex forces during its operation, including:

‌Centrifugal force of rotating mass‌: Due to the high-speed rotation of the crankshaft, its own mass will generate centrifugal force.
‌Gas Inertial Force‌: When the engine is working, the periodic changes in the gas in the cylinder will produce inertial force.
‌Reciprocating inertial force‌: The reciprocating movement of the piston will also produce inertial force.
The combined action of these forces causes the crankshaft to bear bending and torsional loads, so the crankshaft needs to have sufficient strength and stiffness.

‌Structural Design

The structural design of the crankshaft is crucial to its function:

Main shaft journal and connecting rod journal: The main shaft journal is installed on the cylinder block, and the connecting rod journal is connected to the connecting rod, forming a crank slider mechanism.

Crank arm: Connect the connecting rod journal and main journal together to convert the force transmitted from the connecting rod into rotational torque.

Lubrication system: There are radial oil holes drilled on the main shaft journal and the connecting rod journal, which are connected through an inclined oil passage to ensure lubrication effect.

‌Balance and Strength

To improve the fatigue strength of the crankshaft, the journal surface is usually subjected to high-frequency quenching or nitriding, and rounded rolling. In addition, the balance of the crankshaft is also very important. Vibration and wear can be effectively reduced through the design of the counterweight and balance shaft.

‌Summary‌: The working principle of a crankshaft is to transform the linear motion of the piston into a rotary motion, driving other parts of the engine to work while bearing complex bending and torsional loads. Its structural design and material selection directly affect the performance and reliability of the engine.