What Is A Crankshaft? | How does a Crankshaft Work? | What is a Camshaft?

This article deeply describes camshaft and crankshaft. The crankshaft is a type of shaft that drives through a crank mechanism. It consists of a series of crankpins and cranks, and the engine connecting rod attaches to these crankpins and cranks. The crankshaft connects with the piston of the engine through a connecting rod. It attaches inside the block of the engine. It is a mechanical component that aims to convert the reciprocating movement of a piston into rotary motion. Its functions, such as crank and crankpins, contribute to this transformation. So, crankshafts include in the moving components of the IC engine. The crankshaft is a very important component of the engine. The piston is connected to the crankshaft via a connecting rod.

crankshaft

Crankshafts can be in the welded, semi-integral, or one-piece structures. This component of the engine attaches the output body to the input body of the engine. The linear movement of the piston becomes the crankshaft rotatory motion, which further connects with the engine flywheels. Crankshafts are a link that transmits power in the form of rotational kinetic energy. The pistons are linked to the cranking centers by means of connecting rods. The cranking levers enable the pistons to rotate the crankshaft from which the power is taken to drive the wheels of the car eventually.

Construction of Crankshaft:

Materials that can be used based on the requirement:

  • Cast Iron
  • Carbon Steel
  • Vanadium Micro-alloyed Steel
  • Forged Steel

Crankshafts can be assembled from different pieces or made in the form of a one-piece (monolithic). Monolithic crankshafts are very popular, but large and small engines use assembled crankshafts.

Crankshafts can also be cast in ductile steel, modular or malleable iron. Welded constructions are cast in steel. This cost-friendly process is used in cheaper production engines with moderate loads. In spite of being more expensive, forging is the preferred method because of its superior strength.

Casting and Forging Process:

Crankshafts can generally be forged from casts in ductile steels or by roll forging by using steel bars. Nowadays, maximum manufacturers use forged crankshafts because of their excellent inherent damping, compact design, and lightweight. Vanadium micro-alloyed steel mainly uses for the forged crankshaft. This is because these steels can be air-cooled without further heat treatments except the bearing surface hardening once they have reached a high strength. It also has a lower alloy content which makes the material low-cost as compared to high alloy steel.

Carbon steel can be used, but carbon steel requires additional heat treatment to achieve the required material goods. Today, cast iron crankshafts are mainly used in engines with low load and economical production (like Ford Focus diesel engine). Nowadays, only some engines use crankshafts of the cast iron for the cheap and low-power version, while the more costly and high-power versions of engines use forged steel crankshafts.

What is A Camshaft?

The camshaft, located on top of the engine. It is an essential component of the engine valve mechanism, allowing air and fuel to come into the combustion chamber and allow gases to escape after combustion. The latest internal combustion engines can have up to four camshafts (or two camshaft). Each cylinder has four valves (two intake and two exhaust ports). Only a single camshaft setup is configured on each valve. 

Working of Crankshaft:

The crankshaft moves the piston upward and downward in the cylinder. It regulates the motion of the piston. A camshaft also helps to regulate the piston movement properly. As the crank turns, the camshaft must turn too. This is due to the links between these two parts. The movement of these two engine components is synchronized. As the camshaft revolves, the exhaust valve and intake valve open and close. This permits an airflow to enter into the engine cylinder. This is significant to cause an explosion inside the engine cylinder. The explosion takes place in the engine cylinder. This explosion puts pressure on the piston and keeps it moving. The resulting explosion moves the wheels of the vehicle. During this process, the piston gives a jerky movement.

crankshafts working, cam

A flywheel at the end of the shaft helps to alleviate unstable movements. As the shaft starts rotating, then the flywheel moves in a circular movement. The notch inside the flywheel helps to make movement more regular. This movement will eventually turn the wheel since the steering wheel already connects to other components of the vehicles.

Imagine your legs pedaling a bicycle. So instead of the pedals, you have the connecting rod, and your legs are the pistons. So, the reciprocating movement is converted to a rotary motion of the crankshaft. Another example is a diesel gen-sets you have at villages which you crank up with a turning handle to start. You through the lever is rotating the crankshaft to impart initial driving momentum to the engine. 

Parts of Crankshaft

crankshaft parts

1) Main Journal

The main bearing journal is attached to the block of the engine. This engine block rotates around this journal. All crankshaft journals are very hardened, rounded, and smooth. The main journal attaches to the saddle, where a replaceable bearing inserts will attach. These bearings are softer as compared to the main journals, and these can replace when wear. These bearings design to absorb a small number of impurities (if any) to prevent damage to the crankshafts.

Then main bearing cap screws onto the journal and tighten to the particular torque.

The journal of the engine runs over the oil film and is pressed into the space between the bearing and the journal through the holes in the crankshaft seat and the corresponding holes in the bearing inserts. If there are sufficient oil supply and oil pressure, the bearings and journals must not come into contact.

2) Connecting rod journal

The connecting rod journal is offset from the axis of rotation and connected to the larger end of the piston rod. It is also commonly known as rod bearing journal or crank pin. Pressurized oil supplies enter by the main journal from an open-angle oil channel.

Some connecting rods have a perforated oilway so that oil can spray onto the cylinder walls. In this case, the connecting rod’s journal bearing has a groove to supply the connecting rod with oil.

3) Crankshaft lubrication

As metal-to-metal contact is an enemy of efficient engines, connecting rod journal and main journal both move on the oil film that assembles on the bearing’s surface.

Lubricating the main journal bearings is easy. The passage of oil from the block of the engine to each crankshaft seat and the corresponding holes in the bearing housing allow this oil to reach the journals.

The rod journal bearing requires the same lubrication, but it rotates at off-center around the crankshaft. To supply these bearings with oil, the oil channel runs within the crankshaft by the main journals, diagonally by the web, and exit by the hole in the connecting rod journal. The grooves in the major rod bearings drain the oil under the effect of the rotating crankshaft centrifugal force and keep the oil pressed into the channel of the rod journal.

The gap between the bearing and the journal is the chief cause of engine oil pressure. If the gap is too large, the oil will flow freely, and the pressure will not maintain. If the gap is too small, the oil pressure rises, and the metals can come into contact with each other. Therefore, it is necessary to measure the clearance between the journal and bearing when rebuilding the engine.

4) Counterweights

A crankshaft is applied to a strong rotating force, and the mass moves down and up between the connecting rod and the piston applies a large force. The counterweight is cast as the crankshaft’s component to balance these forces. These counterweights make the engine faster and quieter.

The crankshafts balance at the factory. During this process, the flywheel attaches, and the entire assembly rotates towards a machine that can measure the location of the flywheel imbalance. The counterweight has a balance hole to lessen weight. If you need to add weight, make a hole first, then fill it with heavy metal. Repeat this process until the crankshaft comes in balance condition.

5) Thrust Washers

More than two or two thrust washers are installed at specific positions along the length of the crankshaft to prevent it from moving vertically. These washers are positioned between the web’s machined surface and the crankshaft’s seat to maintain a small specified clearance and minimize the lateral movement available to the crankshaft. The distance this shaft moves from one end to the other is known as the endplay, and the tolerance is quantified in the service manual.

Some types of engines form these washers as a component of the main journal bearing, while other engine types (usually older types) use distinct washers.

6) Main Oil Seal

The ends of the crankshaft extend outside the crankcase. So, you need to provide a way to prevent oil from seeping through these openings. This oil seeping problem controls through two main oil seals; one is on the front and the other on the backside.

The rear main seal installs between the flywheel and the rear main journals. Usually, it is a synthetic rubber lip seal. This sealing ring inserts into the groove amid the oil pan and the engine block. The seal has a molded lip that is pressed in contrast to the crankshaft through a spring known as a garter spring.

The oil seal itself is an inexpensive component. But for accessing it demands high labors in eliminating the flywheel, clutch, and transmission; in some cases, the crankshaft takes a lot of effort. Therefore, it is advisable to change the oil seal any time if you can disassemble the engine and access the parts.

Ansys Analysis of Crankshaft:

First of all, we develop all the parts of a crankshaft into the “solid work 2018” and then assemble them then we save his model into an “IGS” format. After that, we import this “IGS” file into the “ANSYS WORKBENCH R15” for Ansys analysis. The Ansys analysis results are given below.

RESULTS AND DISCUSSION:

Analysis of crankshaft-stainless steel is given below.

crankshaft fixed end, cam
                    Fig1: Both ends of the crankshaft are fixed
crankshafts
                                                 Fig 2

As shown in the above fig 2, 3.5 MPa load is applied on the top of the crankpin surface.

Crankshaft, camshaft
                          Fig 3: Crankshaft von-misses stress

The maximum stress induced in the crankshaft is 2.5407e7Mpa at the crankpin neck surface. The minimum stress is 27.342MPa as shown in fig 3.

crankshafts, cams
                                       Fig 4: Maximum Strain

As shown in the above diagram, the maximum strain of the shaft is 152.77MPa.

crankshaft
                              Fig 5: Shaft Total deformation
camshaft, crankshafts
                                Fig 6: Maximum shear stress

The 1.4273e7MPa is the maximum shear stress at the crankpin area as shown in fig 6.

Uses of Crankshaft:

1) Crankshaft controls the motions of all the Valves for inlet, compression, ignition, and expansion and exhaust of the Internal Combustion engine at the correct Timings of the cycle. It is an excellent function.

2) It collects the rotary motion of the connecting rods’ bottom end and delivers it to the flywheel.

How does a crankshaft break?

There is a mechanical concept called fatigue. It means that a material can fail due to repetitive loading. Each time crankshafts rotate, the loads reverse causes a slight flexing of the shaft. It’s much like how you can break a coat hanger or wire by merely bending it back a fourth, maybe a dozen times, and the wire breaks. The flex of a crankshaft is much less, so millions of cycles are required to break it, but the failure mode is the same as the coat hanger. Now, if a bearing supporting the crankshaft fails due to lack of lubrication, the displacement of the deflection per rotation dramatically increases so that failure can occur very quickly.

Another reason for the failure is, an unbalanced flywheel/torque converter or misaligned transmission will be high on the list of a break at the rear of a crankshaft. A stress riser (nick in the finely ground finish) in the radius next to the bearing journal would be another likely cause. The nick can turn into a crack that will propagate quickly.

Is there any engine that works without a crankshaft?

Toyota is developing a unique kind of engine, which is called a Free piston engine linear generator (FPEG).

engine

This is a gasoline engine generator that will be utilized to extend the range of hybrid cars. It might be used in the form of a boxer engine to eliminate vibration in the coming times.

The power generated from FPEG can be directly used to drive an ac induction motor or brushless DC motor. It can also be used to charge the battery pack, which will effectively extend the range of the vehicle.

What is the difference between a Crankshaft and a Camshaft?

Crankshaft

It is the shaft that gives us output from the engine. It is made to rotate by the connecting rod of the piston.

Crankshafts, camshaft

This shaft is made to rotate and take output power from the combustion process in the chamber. The connecting rod is connected to this crankshaft and makes it revolve about its own axis and thereby utilize the power further for use.

This shaft has the main journal and the counterweight. The main journal is over which the connecting rod is mounted. In contrast, the counterweights are used to utilize the inertia of the weights in the further rotation of the crank during the exhaust stroke in the IC Engine’s combustion chamber.

Camshaft

The camshaft is a shaft that drives synchronously with the crankshaft and is equipped with cam lobes that open and close the valve at the right time.

In an internal combustion engine, a simple lifting mechanism on the cam lobes of the camshaft opens and closes the inlet and outlet valves. These cam lobes are those which have a cam profile. As shown in the image below.

camshaft

These cam lobes are mounted on the camshaft, which rotates about its own axis in synchronization with the crankshaft or the shaft, which is the one generating the power from combustion). Due to this type of profile, the valves open and close as the lobe’s nose pushes the pushrod and makes the valves open or close due to the pushing mechanism (they come back because of the spring retracting mechanism of the valve springs).

The belt drive from the crankshaft often powers the camshaft. The belt is called the Timing Belt. Following is the image of two cam lobes being driven by the camshaft with a timing belt.

camshaft assembly

Depending on the camshaft arrangements in the engine corresponding to the valves, the engine is also classified based on SOHC- Single overhead Camshaft or DOHC- Dual Overhead Camshafts (above image).

I hope this detailed Explanation helps you gain more knowledge on this topic.

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