Crankshaft : Definition, Parts, Working, Types, Material, Advantages, Application

What is a Crankshaft?

A crankshaft is a mechanical component in an engine that converts reciprocating motion into rotational motion. It is typically made of forged steel or cast iron and consists of one or more cylindrical sections, known as journals, that are offset from the centerline of the crankshaft.

The crankshaft is mounted in the engine block and rotates on bearings at each end. Pistons are connected to the crankshaft by connecting rods, and as the pistons move up and down in the cylinders, they transfer energy to the crankshaft, which converts the reciprocating motion into rotational motion.

The shape of the crankshaft is designed to ensure that the pistons move smoothly and efficiently through their cycles, with minimum vibration and maximum power output. The offset journals on the crankshaft are carefully positioned to create the correct firing order for the engine, which ensures that the power strokes of each cylinder are evenly spaced and produce the maximum power output.

Crankshafts are essential components of internal combustion engines, including those used in cars, trucks, boats, and generators. They are designed to withstand high stresses and temperatures and are typically machined to very precise tolerances to ensure reliable operation and long service life.

Parts of Crankshaft:

The main parts of a crankshaft include:

1. Main journal: The main journal is the cylindrical section of the crankshaft that sits in the engine block and rotates on bearings. It connects the connecting rods to the crankshaft and transfers the energy generated by the pistons to the crankshaft.
2. Connecting rod journal: The connecting rod journal is the cylindrical section of the crankshaft that connects to the connecting rod, which in turn connects to the piston. This journal rotates with the motion of the connecting rod as the piston moves up and down.
3. Counterweight: The counterweights are additional weights that are added to the crankshaft to offset the weight of the pistons and connecting rods. They help to balance the crankshaft and reduce vibration during operation.
4. Thrust bearing: The thrust bearing is a type of bearing that is used to control axial movement of the crankshaft, ensuring that it remains in position and does not move forward or backward.
5. Flange: The flange is the end of the crankshaft that is used to mount various engine components, such as the flywheel, timing gear, and pulleys.
6. Keyway: The keyway is a small slot cut into the flange of the crankshaft that allows for the mounting of various engine components with a matching key.
7. Fillet: The fillet is the curved area where the main journal and connecting rod journal meet. It helps to distribute stress and reduce the risk of cracking or failure.

Overall, the crankshaft is a complex and precisely engineered component that is essential for the operation of internal combustion engines. Its various parts work together to ensure smooth and efficient energy transfer from the pistons to the engine.

Construction of Crankshaft:

Crankshafts are typically made of forged steel or cast iron and are manufactured using a variety of techniques, depending on the size and complexity of the component. The construction of a crankshaft involves several steps, including:

1. Design: The design of a crankshaft takes into account the engine's specifications, such as the number of cylinders, displacement, and power output. The design will determine the size and placement of the main and connecting rod journals, counterweights, and other features.
2. Forging or casting: The crankshaft may be forged or cast depending on the material and the manufacturing process. Forging involves heating a metal billet and using a press to shape it into the desired shape, while casting involves pouring molten metal into a mold.
3. Machining: After the forging or casting process, the crankshaft is machined to precise tolerances. This involves removing excess material and shaping the various features of the crankshaft, such as the main and connecting rod journals, counterweights, and flanges.
4. Heat treatment: The crankshaft is then heat-treated to improve its strength and durability. This involves heating the crankshaft to a high temperature and then quenching it in oil or water to harden the metal.
5. Grinding and polishing: Finally, the crankshaft is ground and polished to achieve a smooth surface finish and precise tolerances. This helps to reduce friction and improve the overall performance and longevity of the engine.

The construction of a crankshaft is a complex process that requires careful attention to detail and precision machining techniques. A well-made crankshaft is essential for the reliable operation of internal combustion engines, and its construction plays a critical role in the engine's overall performance and efficiency.

Working of the Crankshaft:

The crankshaft is a key component in the engine of a vehicle that converts the reciprocating motion of the pistons into rotational motion that can be used to drive the wheels or other components of the vehicle. The working of the crankshaft involves several steps, including:

1. Intake stroke: During the intake stroke, the piston moves downward, drawing air and fuel into the cylinder.
2. Compression stroke: During the compression stroke, the piston moves upward, compressing the air and fuel mixture in the cylinder.
3. Power stroke: During the power stroke, the air and fuel mixture is ignited by the spark plug, causing a rapid expansion of gases that forces the piston downward. As the piston moves downward, it transfers energy to the connecting rod, which in turn transfers energy to the crankshaft.
4. Exhaust stroke: During the exhaust stroke, the piston moves upward, pushing the exhaust gases out of the cylinder.

As the piston moves up and down in the cylinder, the connecting rod rotates around the connecting rod journal on the crankshaft, which is offset from the centerline of the crankshaft. The rotation of the connecting rod causes the crankshaft to rotate, and the offset journals on the crankshaft convert the reciprocating motion of the pistons into rotational motion.

The counterweights on the crankshaft help to balance the weight of the pistons and connecting rods and reduce vibration during operation. The thrust bearing helps to control axial movement of the crankshaft, ensuring that it remains in position and does not move forward or backward.

Overall, the working of the crankshaft is critical to the operation of an internal combustion engine, and its precise design and construction play a key role in the engine's overall performance and efficiency.

Types of Crankshaft:

There are several types of crankshafts, each with its own unique design and application. Some common types of crankshafts include:

1. Single-plane crankshaft: This is the simplest type of crankshaft, with all the connecting rod journals on the same plane. It is commonly used in inline engines with four or six cylinders.
2. Cross-plane crankshaft: This type of crankshaft has connecting rod journals that are offset 90 degrees from each other, creating a cross pattern. It is commonly used in V8 engines and provides better balance and smoother operation.
3. Flat-plane crankshaft: This type of crankshaft has connecting rod journals that are opposite each other, creating a flat plane. It is commonly used in high-performance engines, particularly those designed for racing.
4. Stroker crankshaft: This type of crankshaft has a longer stroke than a standard crankshaft, which increases the displacement of the engine and can provide more power.
5. Billet crankshaft: This type of crankshaft is machined from a single piece of billet steel, rather than being forged or cast. It is often used in high-performance engines and racing applications because it is stronger and more durable than other types of crankshafts.

The choice of crankshaft depends on the specific application and requirements of the engine. Factors such as the number of cylinders, the engine's power output, and the intended use of the vehicle or equipment will all influence the choice of crankshaft design.

Advantages and Disadvantages of Crankshaft:

Advantages of Crankshaft:

1. Increased Engine Performance: A well-designed and properly functioning crankshaft can increase the performance of an engine by providing smooth and efficient power transfer.
2. Durability: Crankshafts are typically made from strong and durable materials that can withstand the stresses and forces of engine operation.
3. Precision: Modern manufacturing techniques allow for crankshafts to be machined to very precise tolerances, which improves their performance and longevity.
4. Versatility: Crankshafts can be designed to work with a wide range of engines, from small four-cylinder engines to large V8 engines.

Disadvantages of Crankshaft:

1. Complex Design: Crankshafts are complex and precise components that require careful design and manufacturing. This complexity can make them expensive to produce and difficult to repair.
2. High Stresses: Crankshafts are subject to high stresses and forces during engine operation, which can lead to fatigue and failure if not designed and manufactured correctly.
3. Maintenance: Crankshafts require regular maintenance to ensure proper function and prevent damage to other engine components.
4. Cost: High-performance crankshafts made from exotic materials can be expensive, which can add to the overall cost of an engine build or rebuild.

Types of failure in Crankshaft:

Crankshafts are subject to a variety of stresses and forces during engine operation, and as a result, they can experience several types of failures. Some common types of failure in crankshafts include:

1. Fatigue failure: This is the most common type of failure in crankshafts and occurs when the metal is subjected to repeated stresses over time, causing it to crack and eventually fail.
2. Overload failure: This type of failure occurs when the crankshaft is subjected to a sudden, excessive load that exceeds its strength or design limits, causing it to fracture or break.
3. Wear failure: This type of failure occurs when the crankshaft's bearings or journals become worn due to poor lubrication or excessive use, causing the metal to erode and eventually fail.
4. Corrosion failure: This type of failure occurs when the crankshaft is exposed to moisture or corrosive substances, causing the metal to corrode and weaken over time.
5. Manufacturing defect failure: This type of failure occurs when the crankshaft is improperly manufactured or designed, leading to defects in the metal or incorrect dimensions that can cause it to fail prematurely.

The type of failure that occurs in a crankshaft will depend on a variety of factors, including the type of engine, the materials used, the operating conditions, and the quality of the manufacturing and maintenance processes. Regular maintenance and inspection can help to prevent or detect these failures before they cause significant damage to the engine.

Application of Crankshaft

Crankshafts are widely used in internal combustion engines, which are used in a variety of applications including:

1. Automotive engines: Crankshafts are used in gasoline and diesel engines for cars, trucks, buses, and other vehicles.
2. Marine engines: Crankshafts are used in marine engines for boats, ships, and other watercraft.
3. Industrial engines: Crankshafts are used in stationary engines for power generation, construction equipment, and other industrial applications.
4. Aircraft engines: Crankshafts are used in aircraft engines for airplanes and helicopters.
5. Small engines: Crankshafts are used in small engines for lawn mowers, chainsaws, and other small equipment.

In addition to their use in internal combustion engines, crankshafts are also used in other applications where rotational motion is required, such as in pumps, compressors, and other machinery. Crankshafts are also used in some types of electric motors, where they are used to convert the reciprocating motion of a piston or plunger into rotational motion. Overall, crankshafts are a critical component in many types of machinery and play a crucial role in converting reciprocating motion into useful rotational motion.

Difference between Crankshaft and Camshaft

Crankshaft and camshaft are two important components of an internal combustion engine. They both play crucial roles in the operation of the engine, but they have some key differences.

1. Function: The main function of the crankshaft is to convert the reciprocating motion of the pistons into rotational motion, which is used to turn the engine's drive shaft. The camshaft, on the other hand, is responsible for controlling the opening and closing of the engine's valves, which allows the air-fuel mixture to enter the combustion chamber and the exhaust gases to exit.
2. Shape: The crankshaft is typically a long, cylindrical shaft with several offset journals, whereas the camshaft is a shorter, more irregularly shaped shaft with a series of lobes or cams.
3. Location: The crankshaft is located at the bottom of the engine, where it connects to the pistons and the drive shaft, whereas the camshaft is usually located in the cylinder head, where it operates the engine's valves.
4. Timing: The crankshaft rotates continuously during engine operation, while the camshaft rotates only once for every two rotations of the crankshaft. This timing difference is crucial for the proper operation of the engine.
5. Material: Both crankshafts and camshafts are typically made from high-strength materials, such as forged or cast steel, but they may have different coatings or surface treatments depending on their specific functions and operating conditions.

In summary, while both crankshaft and camshaft are important components of an internal combustion engine, they have different shapes, locations, functions, and timing. The crankshaft is responsible for converting reciprocating motion to rotational motion, while the camshaft controls the engine's valves.

Crankshaft Function

The crankshaft is a key component of an internal combustion engine and its main function is to convert the reciprocating motion of the pistons into rotational motion. The pistons move up and down in the cylinders, driven by the force of the combustion of the air-fuel mixture. This reciprocating motion is transferred to the crankshaft through the connecting rods, which are attached to the pistons at one end and to the crankshaft at the other end.

The crankshaft has several offset journals, where the connecting rods are attached, and the rotation of the crankshaft causes the connecting rods to move up and down in a circular motion, which in turn rotates the engine's drive shaft. The rotation of the drive shaft is used to power the vehicle's wheels or other machinery.

In addition to its main function of converting reciprocating motion into rotational motion, the crankshaft also helps to balance the engine and reduce vibration by providing a counterweight to the movement of the pistons. It is also designed to withstand high levels of stress and torque, and must be precisely machined and balanced to ensure smooth operation and long service life.

Overall, the crankshaft is a critical component of an internal combustion engine and is essential to the proper operation and performance of the engine.

Crankshaft Materials:

Crankshafts are typically made from materials that are strong, durable, and can withstand high stresses and temperatures. Here are some of the most common materials used to make crankshafts:

1. Cast Iron: Cast iron is a popular material for crankshafts because of its high strength and durability. It can withstand high temperatures and has good wear resistance, making it ideal for use in heavy-duty engines.
2. Steel: Steel is another popular material for crankshafts, as it has excellent strength, durability, and fatigue resistance. It can also be machined to precise tolerances, allowing for high levels of accuracy and performance.
3. Forged Steel: Forged steel is a type of steel that is heated and then hammered into shape, resulting in a material that is even stronger and more durable than regular steel. Forged steel crankshafts are commonly used in high-performance engines.
4. Billet Steel: Billet steel is a type of steel that is machined from a single block of metal, resulting in a highly precise and uniform material. Billet steel crankshafts are commonly used in racing engines, where accuracy and performance are critical.
5. Aluminum: While less common than cast iron or steel, aluminum crankshafts are sometimes used in lightweight, high-performance engines. Aluminum is lightweight and has good heat dissipation properties, but it is less durable than cast iron or steel and may not be suitable for heavy-duty applications.

Overall, the choice of material for a crankshaft depends on factors such as the engine's power, torque, and operating conditions, as well as the desired level of durability, performance, and weight.

Crankshaft Heat Treating:

Heat treating is an important process in the manufacturing of crankshafts, as it helps to increase their strength, durability, and wear resistance. Here are the main steps involved in heat treating a crankshaft:

1. Preheating: The crankshaft is first heated to a uniform temperature, typically between 800 and 900 degrees Celsius, to relieve any residual stresses in the metal.
2. Quenching: The crankshaft is then rapidly cooled, usually by immersion in a quenching oil or water bath. This sudden cooling causes the metal to harden and increases its strength and wear resistance.
3. Tempering: The crankshaft is then heated again, this time to a lower temperature, typically between 200 and 400 degrees Celsius, to reduce the hardness and brittleness caused by the quenching process. This step helps to improve the crankshaft's toughness and resistance to cracking.
4. Shot peening: In some cases, the surface of the crankshaft may be shot-peened after heat treating to further increase its strength and durability. Shot peening involves bombarding the metal surface with small, high-velocity metal or ceramic particles, which helps to smooth out any surface imperfections and create a layer of compressive stress that can help to prevent fatigue and cracking.

Overall, heat treating is an important process in the manufacturing of crankshafts, as it helps to improve their strength, durability, and wear resistance. The specific heat treatment process used may vary depending on the type of metal used to make the crankshaft, as well as the specific performance requirements of the engine in which it will be used.

Crankshaft Manufacturing Processes:

Crankshafts are critical components of internal combustion engines, and they are typically made using a combination of forging, machining, and heat treating processes. Here are the main steps involved in manufacturing a crankshaft:

1. Forging: The first step in manufacturing a crankshaft is usually forging. This involves heating a billet of metal, typically steel, to a high temperature and then using a forging press to shape the metal into a rough approximation of the final crankshaft shape. Forging helps to align the grain structure of the metal, improving its strength and durability.
2. Rough machining: After forging, the crankshaft is typically rough machined to remove any excess material and bring it closer to its final shape. This may involve using a lathe, milling machine, or other machining tools to cut and shape the metal.
3. Heat treating: The next step is heat treating, as described in the previous answer. Heat treating helps to increase the strength, durability, and wear resistance of the crankshaft.
4. Finish machining: After heat treating, the crankshaft is typically machined again to bring it to its final size and shape. This may involve using grinding, drilling, and other precision machining techniques to achieve the required tolerances.
5. Surface treatment: Depending on the specific application, the crankshaft may also undergo additional surface treatments, such as nitriding or chrome plating, to further increase its wear resistance and durability.
6. Quality control: Finally, the crankshaft undergoes rigorous quality control testing to ensure that it meets the required specifications and performance standards. This may involve using non-destructive testing methods, such as magnetic particle inspection, to detect any cracks or defects in the metal.

Overall, the manufacturing of a crankshaft is a complex and precise process that involves multiple stages of forging, machining, heat treating, and quality control. The specific process used may vary depending on the type of engine and performance requirements, but the end goal is always to produce a strong, durable, and reliable component that can withstand the rigors of engine operation.

Read More: Camshaft: Definition, Parts, Working, Types, Material, Advantages, Application