MBD Simulation on a Piston Assembly

AIM: To create a 3D CAD model of the Piston Assembly and to do motion analysis.

THEORY: A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. ^[1] In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder. ^[2]

DESIGN: The 3D CAD models are designed in SolidWorks and motion analysis is analyzed on Motion Analysis add-on in SolidWorks. The following steps were taken to design the mechanism:-

Step-1: First, a 2D sketch of Piston head was designed and then revolved to get the final part model.

Step-2: Second, a 2D sketch of Wrist pin was designed and then revolved to get the final part model.

Step-3: Third, a 2D sketch of Connecting rod was designed and then extruded.

Step-4: Forth, a 2D sketch of End cap was designed and then extruded.

Step-5: Then Crank was designed by multiple sketching and multiple extruding.

Step-6: Then all parts models were assembled, and constraints were provided.

MOTION ANALYSIS:

Motion analysis was conducted using the Motion Analysis add-on in SolidWorks. The motion features of the SolidWorks provide us a wide range of motion study, they can be divided into three categories:

Animation: If one simply wishes to create some nice visuals for presentation or marketing without consideration of mass and gravity effects, then animation is perfect for it.

Basic Motion: For an extra layer of complexity that takes into consideration the effects of mass, springs, gravity, and physical collision detection, then a Basic Motion study is more suited for the requirements.

Motion Analysis: This is the top tier of motion study and takes into account a wider range of physical interactions such as impact effects, damping, force, momentum, etc. ^[2]

Step-1: Motion Study 1

Wrist pin offset = 0 mm

Piston head moves for 302-203 = 99 mm

Step-2: Motion Study 2

Wrist pin offset = 10 mm positive offset

Piston head moves for 302-202 = 100 mm

Step-3: Motion Study 3

Wrist pin offset = 10 mm negative offset

Piston head moves for 302-203 = 99 mm

Step-4: Superimposition of all 3 graphs

10 mm positive and negative offset both gives a little less linear displacement of piston head, since in both cases wrist pin is not vertically aligned, hence crank does not show full extension, which results in less linear displacement of piston head as in comparison when wrist pin is perfectly vertically aligned.

CONCLUSION:

Providing offset to wrist pin, decreases the linear displacement of piston head.

Google drive link of the model:

https://drive.google.com/drive/folders/1WSPqQvHUAlIUlwteLNeYAsxo6yBdMAQ1?usp=sharing

REFERENCES:

[1] "What is the difference between OHV, OHC, SOHC and DOHC engines?". www.samarins.com. Retrieved 23 January 2020.

[2] Cranswick, Marc (2011). The Cars of American Motors: An Illustrated History. McFarland. p. 80. ISBN 9780786446728. Retrieved 29 January 2014.