A crank mechanism drives the crankshaft, which is a rotating shaft. It is a mechanical device that converts the piston’s linear movement into a rotating motion. A crankshaft is a key component of an engine’s power transfer system. Located within the engine crankshaft block, it uses a connecting rod to transform the pistons’ reciprocating motion into a rotational one.
In this reading, we’ll learn what a crankshaft is, its function, diagram, components, and how it works.
Let’s get started!
What Is A Crankshaft?
A crankshaft is a rotating shaft that converts the reciprocating motion of a piston into a rotational motion. It’s commonly used in internal combustion engines to perform such operations. Crankshafts consist of a series of cranks and crankpins to which the connecting rods are attached. A crankshaft with at least one shaft rotates within the engine block. It rotates using the main bearings. The crankpins rotate within the connecting rods using rod bearings.
Functions
The function of crankshafts is to give a smoother drive to the vast motors with multi-cylinders. The linear motion of the pistons is changed into a rotational motion. In the combustion of the fuel-air mixture, power is produced. This power is transformed into the rotary movement of the crankshaft.
The linear motion of the pistons is converted via the connecting rod into torque. It’s then passed to the flywheel. The crankshaft’s shaft is bored with some holes that feed the motor with oil. This oil smooths the movement.
The counterweights aid the adjustment of the framework and the heaviness of the connecting rod. Crankshafts also function as load-bearing, as some load is withstanding during the process. One of the loads is severe bending and torsional stress.
As the rotary movement of the crankshaft is constantly being accelerated and decelerated, further loads from torsional vibration are added. Bearings also experience a high degree of wear.
Diagram Of A Crankshaft
Components Of A Crankshaft
There are a number of interdependent components that make up a crankshaft. The following are the major parts of the crankshaft:
Main Journals
The crankshaft journals serve as an attachment point for the engine block. They have bearings that enable the engine block to spin around the crankshaft while keeping it in place. In the main journals, you may find two different kinds of bearings: plain bearings and journal bearings.
Counterweights
These weights are primarily used to apply opposite force; they are positioned on the crank web. Counterweights enable the crankshaft to achieve the necessary stability and balance.
Flywheel Mounting Flange
The flywheel is attached to the crankshaft at the flywheel mounting flange. A bigger flywheel flange on one end of the crankshaft provides a surface to install the flywheel.
Crank Pin
This component of the crankshaft provides a solid connection between the connecting rod and the crankshaft. Rod bearing journal and connecting rod journal are other names for this part. The surface of a crank pin is always cylindrical. This surface makes sure the pin rotates with the same force as the larger end of the piston rod.
Web Crank
The crank web connects the main bearing journals to the crankshaft. This is the most crucial part of the crankshaft.
Thrust Rods
The crankshaft would undergo vertical movement in addition to its rotational motion in the absence of thrust washers. Placing two or more thrust washers in strategic locations along the crankshaft’s length helps to avoid these issues. Additionally, to ensure a certain amount of space between the crank web and shaft, washers are positioned between the web’s surface and the crankshaft saddle.
Oil Seals
Openings are present on both extremities of the crankshaft, as it extends beyond the crankcase. Using oil seals is one technique to stop oil from leaking out of the crankshaft. The crankshaft has two primary oil seals: one at the front and one at the back. The timing gear and pulley are in front of the front-end oil seals. It is simple to replace this oil seal since it is accessible.
Crankshaft Lubrication
Lubrication plays an important role in an engine’s efficiency as its working mechanism involves the robbing of two metal parts. To avoid unnecessary wear on the crankshaft, the main journals and rod journals both ride on a film of oil.
This film of oil sits on the bearing surface. The oil is supplied to the main bearing through the oil galleries from the engine block. It leads to each crankshaft saddle, and the matching hole in the bearing shell collects the oil to the journal.
How A Crankshaft Works
The working of the crankshaft is quite interesting and easy. There is a distance between the center of the main journal and the center of the crankshaft pin. This distance is known as crank radius or crank throw. Its measurement determines the range of piston travel as the crankshaft rotates. The distance from top to bottom is known as a stroke. The piston stroke is twice the crank radius.
The rear end of the crankshaft extends outside the crankcase and is supported with a flywheel flange. This flange is a precision-machined part that is bolted to the flywheel. Its heavy mass allows smooth pulsation of the pistons, firing at different times.
Flywheel rotation makes its way through the flywheel, transmission, and final drive to the wheels. Crankshafts are bolted to the ring gear in an automatic drive. It carries the torque converter and passes it to the automatic transmission.
Common Crankshaft Problems
Problems only arise when the engine is running in severe conditions; they seldom impact the crankshaft. The engine part is sturdy and reliable, yet typical issues include:
Worn Journal
This is caused when there is not enough oil pressure. The crankshaft journals make contact with the bearing surfaces. This gradually increases the clearance and worsens the oil pressure. Worn journals can cause serious problems to the engine if care is not taken. It leads to destroyed bearings and huge damage to the engine.
Fillet Fractures Due to Constant Forces
This is when constant forces on the crankshaft lead to fractures. This problem usually occurs on the fillet where the journals and the web are joined. A smooth radius of the fillet is critical to avoid weak spots, which lead to fatigue cracks. Cracks can be inspected on the crankshaft using a magnaflux.
