Representation of a Crankshaft and its Important Components, Engine Diagram

The core of any reciprocating engine is the cranktrain, made up of the crankshaft, connecting rods, pistons, and the flywheel. Even though this thesis will be focused primarily on the crankshaft, connecting rods and their configurations will also be addressed. “A crankshaft is a mechanical part able to perform a conversion between reciprocating motion and rotational motion”. The main purpose of this conversion is to create useful work. In an internal combustion engine, the reciprocating motion of the pistons connected to the crankshaft via connecting rods is transformed into rotational motion which is eventually transferred to the wheels of the vehicle. In the case of a piston compressor, the rotational motion (provided by either a viscous fluid, electric motor, etc.) is converted into reciprocating motion consequently compressing a fluid.  

A crankshaft is made up of at least two centrally located coaxial axes, known as “main” journals, and one or more offset axes, known as “rod” or “crankpin” journals or crank throws. The main journals get their name since they house the supporting or “main” bearings which attach to the crankcase. As the main journals rotate around its own axis, the crankpin journals describe a circle whose diameter is twice the size of its offset with the main journals. This diameter described by the crankpin journals is also the engine stroke, which is the distance the piston travels in its cylinder.  

As seen in the figure above, the primary drive typically has a flywheel attached to reduce characteristic four-stroke engine vibrations and to conserve inertia maintaining smoother power delivery to the rest of the vehicle components.  

The connecting rod, also known as conrods, is an important component of the crankshaft since it exerts forces on the crankshaft of important characteristics that will later be studied during the analyses portions of the thesis. The simplest representation of a connecting rod is a beam with two pins on both of its ends as shown in figure 1.2. The end of the connecting rod attached to the crankshaft suffers high rotational speeds while the opposite end, attached to the piston, suffers from lower rotational speeds. It is one of the components that suffers the most stress in the engine

Source : Victor Berruga Garcia & Juan Norverto Moriñigo