Looking at the shape of the crankshaft design, you may ask a question: Why is a crankshaft design not designed straight?
The crankshaft is not designed straight so that it will lessen engine vibration, have a weight balance, be smooth running, and maintain the right power interval angle.
When I was invited for an interview, the interviewer asked me why the crankshaft shape was zigzag, not straight.
I answered that it is for balance, smooth running, and less vibration. That is how I got the job.
Are you interested in reading another article on crankshaft?
Keep reading below for more details.
Why Is The Crankshaft Design Shaped The Way It Is
Looking at the crankshaft, you will observe that its shape is not straight; rather, it is zigzag. This article explains why the shape is not straight.
Read below for four reasons why the crankshaft shape is not straight.
1. Less vibration: If the crankshaft shape is straight, the engine will vibrate due to imbalance. In a single-cylinder engine, when the piston is at the TDC, the crankshaft weight is down to compensate for the weight of the piston.
In a multi-cylinder engine, the firing order ensures the working sequence of each cylinder.
2. Smooth running: The shape of the crankshaft design helps the engine run smoothly. For example, in a 6-cylinder engine, the crankshaft allows only 2 pistons to be in the same position together but at different strokes.
3. Maintain the right power interval: The crankshaft does not have to rotate too far before another power stroke.
You need to remember that the power stroke keeps the engine running.
The flywheel stores energy between each power stroke until the next power stroke forces the engine rotation.
But if the crankshaft is straight, the interval of the power stroke will be too long, which will affect the engine rpm and the whole engine functionality.
4. Weight balancing: If the crankshaft design is straight, it will break due to the imbalance in weight caused by the piston weight.
Imagine a 6-cylinder engine with all the pistons at the TDC at the same time. No doubt, the weight will be imbalanced and break the crankshaft.
For the engine to maintain sufficient balancing, all the pistons must not be in the same position, which can only be achieved by a crankshaft design shape that is not straight.
What Materials Are Used In The Manufacturing Of Crankshaft
Currently, crankshafts are made from forged steel, nodular iron and austempered ductile iron.
The fatigue resistance obtained with forged steel is higher than that produced by a nodular or ductile cast iron material.
Manufacturing by forging has the advantage of obtaining homogeneous parts without pores and microstructural defects, such as those presented in a foundry.
Furthermore, the directionality of the properties due to the forging process increases the resistance in the direction of grain deformation.
Grain directionality is an indicator of forging quality and strength directionality.
Alloy steels have all the mechanical properties required to manufacture high-strength crankshafts.
Medium-carbon alloy steels, such as SAE 4340, contain carbon percentages ranging from 0.25% to 0.45%.
These steels contain small percentages of manganese, chromium, molybdenum, nickel, silicon, cobalt, vanadium, niobium and titanium.
These alloying elements improve hardenability, nitriding, hardness, tensile strength, yield, fatigue resistance, flexibility, impact and corrosion.
It is important to point out that these steels must be as clean as possible, that is, eliminate as far as possible the sulfur and phosphorus that reduce the mechanical properties of these steels, making them brittle.
For this reason, some alloys are melted in a vacuum, which undoubtedly increases the cost of these steels.
What Is The Manufacturing Process Used For Crankshaft Development
Due to their complex demands, crankshafts are usually manufactured by forging, as this can produce the necessary hardness and flexibility.
However, production mainly occurs through processes that consume a lot of energy and are characterized by removing flash as rework.
At the Institute for Integrated Production Hannover (IPH), a four-stage sequence of stages for producing a precision-forged, burrless two-cylinder crankshaft was therefore researched.
The procedural steps are:
- Cross wedge rollers,
- transverse extrusion,
- multi-directional forging and
- Finish forging.
Cross-wedge rolling creates a pre-distribution of mass on a cylindrical blank, so areas later formed into crank webs have a higher volume.
What Is The Movement Of The Crankshaft
The movement of the crankshaft refers to rotary motion.
During the fuel combustion, the piston shoots directly down into the cylinder.
The crankshaft’s job is to convert this linear motion into rotation, basically turning and pushing the piston up the cylinder.
To find a more graphic simile, the crankshaft of your vehicle does the same work as the crank of a bicycle, which converts the up and down movement of the legs – more or less – into a rotation that makes the chain turn and this, in turn, is the axle of the rear wheel.
A crankshaft has to withstand enormous forces, sometimes exceeding 9 tons.
As expected, the pressure of the combustion chamber creates a significant force, which knocks the piston and connecting rod downward.
What Is The Relationship Between The Movement Of The Piston And The Crankshaft
The movement of the crankshaft determines the movement of the piston, and the shape of the crankshaft determines the position of the piston in a cylinder.
Since the crankshaft is not straight, the rotation determines which piston goes up and which one comes down.
In a multi-cylinder engine, two pistons are synchronized together, with similar positions in the cylinder but different strokes.
The crankshaft transforms the engine’s combustion force into rotary motion. The connecting rod transforms the pistons’ linear upward and downward movement into torque and is transmitted to the flywheel.
The piston connecting rod group is the transmission part of the engine. It causes the crankshaft to revolve and provide power by transferring the combustion gas’s pressure.
The piston connecting rod group mainly comprises a piston, a piston ring, a piston pin and a connecting rod.
The crankshaft flywheel set aims to transform the piston’s reciprocating motion into the crankshaft’s rotational motion and output torque, which powers the vehicle and other devices that need power.
What Is The Design Of The Crankshaft
The crankshaft is one of the engine’s most essential parts. It is subjected to severe work and requires an appropriate choice of material and precise machining.
It is composed of supports (or necks), elbows, crank arms, and two conductive ends. An elbow with two crank arms: Between two supports, there may be one, two, or even three cranks, but only rarely four.
Most modern automobile engines have several main bearings equal to the number of cylinders plus one when they have more than two.
Commonly, the crankshaft is forged or cast in a single piece (automobiles), but in special cases, it comprises different parts joined together.
This mechanism is the starting point of systems that use the rotary movement of an axis or a shaft to obtain alternative linear or angular movements.
However, it is also essential for the opposite: producing turns from alternative or oscillating linear movements.
What Are The 4 Main Components Of A Crankshaft engineering
The crankshaft is designed to have a tough core and robust surfaces to withstand wear due to its constant rotational motion. Its main components are:
1. Main Journals : This runs in the bearing and determines the axis around which the shaft rotates.
2. Crank pins: The crank pins are connected to the connecting rods.
3. Crank webs: The crank webs connect the crank pins to the main pin.
4. Counterweights: As the name suggests, they provide weight balance in the crankshaft by reducing the load on the main bearing.
They are either attached directly to the crankshaft or connected via the crank webs.
What Are Three Functions Of A Crankshaft
The crankshaft is one of the important parts of a car engine since it is responsible for transforming the reciprocating rectilinear movement into uniform circular motion and vice versa.
To understand why this part is so important, you have to know what exactly its role is in a car’s operation.
The explosions inside an engine’s combustion chambers push the pistons downward.
This movement is transmitted to the connecting rods, which rotate the crankshaft like bicycle pedals.
The elements that make up the crankshaft continually rub, which can cause wear in the bearings. This problem is solved by changing them for new ones.
Other times, the wear originates in the supports or the crankpins.
In this situation, it is necessary to repair it before the engine begins to fail and break down, making the repair much more expensive.
What Are The Three Types Of Crankshaft Design
There are two main families of crankshafts: composite models and monolithic models.
The first is composed of several elements. They are particularly adjustable according to the desired timing of the engine.
These parts are fitted to single-cylinder or twin-cylinder blocks since they generate more vibrations.
Over time, play may appear in certain components. However, these crankshafts can be disassembled and reassembled to resolve this problem.
That said, they are not suitable for high-displacement blocks.
Monolithic crankshafts equip engines with more than 2 cylinders.
These parts were forged using a single block of carbon-enriched steel, making them much more robust and durable.
On the other hand, timing promises to be more difficult during a general engine overhaul.
All connecting rod-crank systems must be perfectly synchronized, and the pistons must fully stretch with each rotation.
Final Thought
The crankshaft design is not a straight shaft, and it was designed to optimize the engine’s performance. The crankshaft rotation determines the piston movement.
You should remember the manufacturing process used to manufacture the crankshaft.
The crankshaft design is important in reciprocating engines, and the features are relevant to the engine’s functionality.
The article also discussed relevant questions such as what are the three types of crankshaft, what are three functions of a crankshaft design, what are the 4 main components of a crank.
You also have another article here to read still on crankshaft.
What type of crankshaft do you have?