A crankshaft converts the linear energy of the pistons into rotational energy in an engine. The rotational motion then transfers through the gearbox to the wheels.
A crankshaft is also referred to as a crank and has four main parts, which are the main journals, the connecting rod journals, the piston assembly and a flywheel in some engines. Other parts include webs, pins, throws and rear main bearing journal.
The main journals are the most significant parts as they act as support points and the center of rotation for the crank. In most crankshaft assemblies, the main journals as well as the connecting rod journals have a hollow construction that helps boost the crank’s torque capability in addition to reducing the total weight of the assembly.
In manual transmission engines, the flywheel is the point at which the engine and the drive train connect. In automatic transmission engines, the connecting point is called a torque converter.
The crankshaft is set in motion when compressed air and fuel ignites, resulting in a powerful force that is exerted on top of the pistons. When the pistons move down into the cylinder, the connecting rods push against the crankshaft.
The crankshaft is designed to move in a rotary motion when the connecting rods apply force to it as opposed to the up and down motion of the pistons and connecting rods.