Crankshaft

The crankshaft converts the reciprocating motion of the piston into rotational motion. This blog post provides knowledge about crankshaft, crankshaft material, crankshaft function. This blog is about the crankshaft, types of the crankshaft, functions of the crankshaft. This blog post provides knowledge about crankshaft, crankshaft material, crankshaft function, types of crankshaft.

Content

• Functions of crankshaft
• How does crankshaft work?
• Construction of Crankshaft
• Functions of crankshaft parts.
• Types of crankshaft
• Key design parameters of Crankshaft
• How crankshafts are manufactured
• Quality control and Quality assurance in crankshaft manufacturing
• References

Let’s understand meaning of crankshaft & functions of crankshaft.

1. It transmits the power from the engine cylinder to the flywheel and gearbox.
2. The crankshaft helps to maintain the firing order of the engine.
3. The crankshaft balances engine dynamics, vibrations, centrifugal forces.
4. It provides drive to the camshaft, engine fuel pump, water pump, oil pump, engine alternator, steering pump, and A/C compressor. 

How does crankshaft work?

Please watch the below GIF to understand how does crankshaft works.

The above animation helps to understand how the reciprocating motion of the piston is converted into a rotational motion. In a multi-cylinder engine, the crankshaft must maintain engine dynamics without affecting the firing order of each cylinder. The power generated by the crankshaft is further transmitted to the camshaft by toothed belt drive (known as timing belt) of by chain (known as timing chain). Timing chains are mostly used for a single-cylinder engine where space is constrained.

Construction of Crankshaft

1. Main bearing journals
2. Crankpin
3. Flywheel end
4. Crank web & Balancing weight
5. Oil hole and oil passage
6. Pulley end

Let’s understand the functions of each section of the crankshaft parts.

1. Main bearing journals: Crankshaft main bearing journal works as a pivot point, it forms an axis of rotation. The crankshaft main journal bearing surface must be free from irregularities as it is subjected to rotational and centrifugal forces. For in-line cylinder engine number of main bearing journal = Number of cylinder + 1.
2. Crankpin: The function of crankpin is to provide a pivot point for connecting rod. The distance between the crankpin radius and crankshaft is known as the crank radius.
3. Flywheel end: At this section of the crankshaft flywheel mounted.
4. Crank web & Balancing weight: Crankweb provides mechanical strength to the crankshaft in order to withstand high centrifugal forces. Counterweights provide a balancing effect on the piston and connecting rod. As the crankshaft rotates at a higher speed, it’s very necessary to balance centrifugal force. 

Crankshaft types:

Depending on the number of cylinders crankshaft types decided.

Key design parameters of Crankshaft:

1. The crankshaft should withstand high centrifugal forces generated due to the reciprocating movement of piston and cylinder at high speed.
2. The crankshaft must withstand high working temperatures.
3. The crankshaft must withstand torsional load/stress during the power stroke of each cylinder.
4. The smooth surface finish on the crankpin and main journal bearing must be maintained to avoid wear and tear of an engine bearing.
5. The crankshaft must sustain the axial load generated due to the clutch spring load.
6. The crankshaft must have good fatigue strength.
7. Geometric tolerances and dimensions on the crankshaft must be maintained in a proper way for smooth functions of engine components like a piston, connecting rod, camshaft, valves, etc. Refer following animation, how the crankshaft drives other engine components.

How crankshafts are manufactured? (crankshaft material)

Casting is the most common manufacturing method used for the crankshaft. The forging method is also used for crankshaft manufacturing. After forging machining operation is necessary to maintain a smooth surface finish on the crankpin and main journal bearing surface.

Quality Assurance and Quality Control in Crankshaft manufacturing

Smooth functions of the crankshaft are very essential for better engine efficiency. Engine with defective crankshaft turns in to the poor performance of the engine. Following Quality assurance and Quality control methods mostly used in industry,

Quality Assurance	Quality Control
Design FMEA	Identification of Crankshaft with serial number.
Process FMEA	Traceability of crankshaft with raw material and lot/batch number.
Engine system FMEA	Metallurgical inspection of raw material
Forging Process control plan	Crack testing – To detect internal cracks in the crankshaft
Casting Process Control Plan	Fatigue & Durability test of crankshaft
Reliability and Durability testing	GD&T inspection – Perpendicularity, parallelism, datum, circularity, surface finish
Verification & Validation	Stastical Process Control eg. Histogram

Reference: ISO 7967-2:2010(en)
Reciprocating internal combustion engines — Vocabulary of components and systems — Part 2: Main running gear.

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