Introduction / History 

Although a crankshaft may appear to be just another part tucked away in the intricate workings of an automotive engine, its job is essential to the engine’s operation. Imagine the crankshaft as the engine’s skeleton, shifting the pistons’ up-and-down motion into a rotating movement that powers your car’s wheels. This essay will delve into the crankshaft, helping us understand its intricate workings and appreciate the complex motions happening beneath every car’s hood. I’m willing to bet that when you think of a crankshaft you think of well this  [Figure 1]  and that you strongly associate crankshaft with internal combustion engines    well the truth is that crankshaft are way older than internal combustion engines as a matter of fact they’re ancient the first instances of a crankshaft date back as far as In 1206, the Arabic inventor, Al-Jazari, described the earliest known crankshaft, which he incorporated with a crank and connecting rod mechanism in his twin-cylinder pump. Al-Jazari’s mechanism consisted of a wheel setting several crank pins into motion. His water pump also employed the first known crank-slider mechanism [Figure 2]. And some  200 years BC in the Western Han Dynasty in China here crank shafts were used to hand operate a quern [Figure 3] which is a primitive stone tool that’s used to grind grain into flour but all crankshafts whether those that are hand operated quern of the Western Han Dynasty or those inside a ten thousand horsepower top fuel dragster both  have the same purpose to convert the reciprocating motion into rotary motion. This principle of converting reciprocating motion into rotary motion is the reason why we use crankshafts. Here’s something from the Roman times [Figure 4] as you can see here the rotary motion of the watermill is converted into reciprocating motion via a crank and an actual connecting rod with the end result of sawing logs in half and while the purpose has remained the same the leaps in technology resulted in a massive evolution of the crankshaft from a simple wooden hand operated machine to a high precision high strength metal piece of amazing engineering capable of sustaining thousands upon thousands of horsepower and prolonged exposure to very extreme forces.

[Figure 1]   “Crankshaft.” Haynes, 11 May 2024                           [ Figure 2] “Pump and Crankshaft Diagram.” Al-Jazari’s Book of Knowledge of Ingenious Mechanical Devices, 10 July 2019

Figure 3] “Quern” Wikipedia, May 11 2024  

[Figure 4]: Hierapolis sawmill, Wikipedia, Retrieved May 11, 2024

  Parts and Descriptions

Before diving into the world of the crankshaft, it’s essential to understand its various components and functions. The main journals and rod journals are critical parts of all internal combustion engine crankshafts. The main journals (Figure 5) are the sections on which the crankshaft rotates. These journals are secured in the engine block by main journal bearing caps.

Rod journals [Figure 5] , which are typically smaller than main journals , are also known as crank pins or big end journals. They are referred to as big end journals because they connect to the big ends of the connecting rods. The rod journals are linked to the main journals via crankshaft webs. The distance between the centerline of the main journal and the rod journal, called the crank throat or crank radius, determines the engine’s stroke—the up-and-down travel distance of the piston. The engine stroke is always twice the crank radius.

At the end of the crankshaft, you’ll find the flywheel flange (Figure 5), where the flywheel is attached. The flywheel, with its heavy round mass, smooths out the pulsations of combustion inside the engine. These pulsations occur at different times, and without a flywheel, the engine would run much less smoothly. On the opposite end of the crankshaft is the nose, where the crankshaft pulley is attached.

Counterweights [Figure 6], those large chunks of metal on the crankshaft, balance the forces generated by the piston’s mass, pin, rings, and connecting rod moving at high speeds. The oiling holes in the rod and main journals play a crucial role in engine lubrication. Engine oil is picked up from the sump ( also known as the oil pan) by the oil pump and sent through the block to the crankshaft. These oiling holes create a film of oil that prevents metal-to-metal contact between the crank journals and the rod and main bearings.

A critical design element of the crankshaft is the radius fillet [Figure 7] . Engineers meticulously design the radius fillet to prevent the crankshaft from breaking apart. This design spreads the load and relieves stress at points that would otherwise be prone to stress fractures. A sharp-angled design is much more susceptible to fractures compared to one with a properly machined fillet. 

[Figure 5] How a Car Works. (n.d.). Crankshaft diagram. Retrieved May 11, 2024, from https://www.howacarworks.com/crankshaft

[Figure 6] ScienceDirect. (n.d.).  

Crankshaft with main bearings 

and counterweights. Retrieved May 11, 2024     [Figure 7] How a Car Works. (n.d.). Crank radius 

diagram. Retrieved May 11, 2024

Outline

Main Journals

The crankshaft journals connect the crankshaft to the engine block, using bearings to keep it in place while allowing smooth rotation. There are different types of bearings, such as journal and plain bearings, and the type used depends on the engine’s torque. Counterweights, mounted on the crank web, balance the crankshaft by applying an opposite force. They ensure stability, prevent speed-reducing reactions, and help the crankshaft achieve high RPMs.

Flywheel Mounting Flange

The flywheel mounting flange is where the crankshaft connects to the flywheel. This part of the crankshaft is usually larger, offering a stable surface for securely attaching the flywheel.

Rod Journals

Rod journals are where the connecting rods attach to the crankshaft, linking the pistons to it. As the pistons move up and down, these rods rotate around the rod journals, transforming piston motion into the rotational force that powers your car’s wheels.

Counterweights

Counterweights are heavy, well-placed weights on the crankshaft that balance it as it spins. By offsetting the weight of the pistons and connecting rods, they reduce vibrations, making the engine run smoother and last longer. This clever balancing act ensures your engine operates efficiently and reliably.

Radius Fillet

 A radius fillet is a rounded edge where the crankshaft’s rod journals and main journals meet the shaft. This small yet crucial feature reduces stress at these junctions, preventing cracks that could start at sharp corners. By smoothing out these edges, the crankshaft becomes stronger and less likely to crack under the engine’s heavy forces.

   Function

The crankshaft is a vital part of a car’s engine. Its main job is to convert the up-and-down motion of the pistons into a rotating motion that powers the car’s wheels. Here’s how it works: What it does: The crankshaft takes the vertical movement of the pistons and turns it into a rotational motion. This rotation is what eventually makes the car move. Why it does what it does: The engine needs to turn the pistons’ movement into something useful for the car’s wheels. The crankshaft does this by using a series of cranks and rotating it, so the pistons’ energy is converted into rotational energy. How it does it: The crankshaft is connected to the pistons via connecting rods. As the pistons move up and down, they push and pull on these rods, which makes the crankshaft rotate. This rotation is then transferred through the transmission to the car’s wheels, making them turn and propel the car forward.

Conclusion

In conclusion, the crankshaft is a fascinating piece of engineering magic. It turns the simple piston movements into the powerful rotations that make our cars go. This isn’t just about function; it’s about the incredible beauty of how all these parts work together so seamlessly. The crankshaft’s elegant design and crucial role remind us of the hidden artistry and precision that make driving possible.

References- 

Walker, J. (2023). The essential functions of the crankshaft in car engines. Automotive

Engineering Journal, 45(2), 123-130.

Vicky. (2023, February 10). What is crankshaft: Everything you need to know. AutoProtoWay. Retrieved May 11, 2024, from https://autoprotoway.com/what-is-crankshaft/

Wikipedia contributors. (2024, January 30). Hierapolis sawmill. Wikipedia, The Free Encyclopedia. Retrieved May 11, 2024, from https://en.wikipedia.org/wiki/Hierapolis_sawmill

What is a car crankshaft? Haynes. Retrieved May 11, 2024, from https://haynes.com/en-gb/tips-tutorials/what-is-car-crankshaft

Author Unknown. (n.d.). Crankshaft. History Fandom. Retrieved May 11, 2024, from https://history.fandom.com/wiki/Crankshaft#:~:text=In%201206%2C%20the%20Arabic%20inventor,several%20crank%20pins%20into%20motion. Wikipedia contributors. (2024, May 16). Crankshaft. Wikipedia, The Free Encyclopedia. Retrieved May 11, 2024, from https://en.wikipedia.org/wiki/Crankshaft