Before the advent of electric starting systems, cars were started by manually cranking the crankshaft. When you drive to the grocery store to pick up food for your family, it is the crankshaft in your car's engine that helps to make this possible. But what, exactly, is a crankshaft, and why do the vast majority of internal combustion engines have one?
The crankshaft, which is one of a series of links between the pistons and the drive wheels, is a one-piece part located in the bottom end of the engine that harnesses the huge forces produced by the explosions in the combustion chamber. The front end of the crankshaft, known as the snout, turns the sprocket, or timing gear, to drive the camshaft. The snout also turns the drive pulley that runs a belt connected to the alternator, fan, water pump and power steering. The other end of the crankshaft is connected to the flywheel, which is toothed, allowing the starter motor to rotate the crankshaft.
When the spark plugs ignite the fuel-air mixture in the combustion chamber, the resulting explosion forces the pistons downward with tremendous force. The function of the crankshaft is to change the up-and-down motion of the pistons to a rotating motion. This is accomplished by having the connecting rods (which are attached to the pistons) connect to the crankshaft in an offset manner, so that as they go up and down their angle changes. This can be easily seen in the video link supplied with this article.
A crankshaft has what are known as "journals," counterweights, a crankshaft snout and a crankshaft flange. The crankshaft main journals are where the crankshaft fits into the engine block's main bearings. The crankshaft rod journals are where the connecting rods are bolted to the crankshaft. The counterweights, which are formed right into the crankshaft, serve to balance the crankshaft and prevent vibration. The journals are specially machined and polished to ensure smooth operation of the engine. The flywheel bolts to the crankshaft flange.
The first engines to make use of a crankshaft used a cast-iron crankshaft, but today's crankshafts are typically made with cast or forged-steel alloys and sometimes a material known as ductile iron (nodular or spheroidal graphite). Because a crankshaft is sometimes supported in only two places, it must be strong. In addition, the wear between the crankshaft and the bearings necessitates the metal be hardened.
The engines in the tractors that tilled the fields that grew the produce you bought at the store rely on a crankshaft, as do the truck engines that delivered it to the store. Gasoline by itself is useless, but for an internal combustion engine that employs pistons to be of any use, the crankshaft is the engine part that allows the engine output to be rotational. Since most vehicles are based on the principle of the wheel, the benefits of the crankshaft are readily apparent.
