MBD Simulation on a Piston Assembly

AIM:  To design parts and assembly of Piston in solidworks and then do the motion analysis for different condition.

OBJECTIVES:  

• To model all the components of piston assembly
• To make assembly of the piston.
• To do motion analysis for three different cases
• To Obtain the Linear displacement of the Piston Head in all the three cases.
• Then Export the data to excel and create the three plots and then Superimpose all the three graphs into a single graph

INTRODUCTION:

Piston:

• A piston is a component of reciprocating engines, reciprocating pumps, gas compressors 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.
• 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.

 

INPUTS:

Different conditions:

Sr.no.	Wrist Pin Offset	Crank Speed (Rpm)
1	"0" mm	2000
2	10 mm Positive	2000
3	10 mm Negative	2000

 

3D MODELS:

• Crank

The crank is a moving part of the internal combustion engine (ICE). It's main function is to transform the linear motion of the piston into rotational motion. The pistons are connected to the crank through the connecting rods.

• Connecting rod

Often shortened to conrod or rod, the connecting rod is one of the most important piston parts. It links the piston to the engine’s crankshaft and moves the piston in and out of the combustion chamber. Connecting rods have to bear a lot of mechanical strain and should be sturdy enough. For this reason, the parts are mostly forged, although casting is also frequently used.

• End cap

End cap is connected to the end of the connecting rod

• Piston

A piston is a moving disk enclosed in a cylinder which is made gas-tight by piston rings. The disk moves inside the cylinder as a liquid or gas inside the cylinder expands and contracts. A piston aids in the transformation of heat energy into mechanical work and vice versa. Because of this, pistons are a key component of heat engines. Pistons work by transferring the force output of an expanding gas in the cylinder to a crankshaft, which provides rotational momentum to a flywheel. Such a system is known as a reciprocating engine.

• Wrist Pin

A pin joining the end of a connecting rod to a trunk piston or the end of a piston rod.

• Assembly of piston

SETUP EXPLANATION:

• To design the assembly first we will start with the modeling of the components. The first thing that we are going to model is the crank .The sketches are to be done in the front plane so as to get a proper graph during the analysis.
• Further we will model connecting rod and end cap .All the components are to be sketched in front plane.
• Then we will model piston and the wrist pin.
• Further using the components we will model the assembly, the assembly is done in the front plane as well.
• Now we have 3 different cases, in the first cases we have 0mm offset of wrist pin .After making sure that the wrist pin has no offset we will the go for motion analysis.
• In motion analysis we are going to first provide a motor for the crank to rotate, then we will give the solid bodies contact for all the components accordingly. Then further we will provide the Frame per seconds i.e. 7200 and also enable the precision contact. Then we will add the gravity along the y axis. After this we will set the End point time to 0.2 sec and then click on calculate and then once the calculation is done we will go for plotting of the graph.
• To plot we will select the linear displacement option and for the face, we will select the top face of the piston and get the linear displacement.
• Then we will provide a 10mm negative offset as shown in the figures in the output plots section and then follow the same procedure and get the linear displacement.
• Similarly we will get the plot for 10mm positive offset.

OUTPUT PLOTS:

Case1:  0 mm wrist pin offset

• Solidworks plot:

• Excel Plot:

Case2:  10 mm negative wrist pin offset

• Solidworks plot:

• Excel Plot:

Case 3 :  10 mm  positive  wrist pin offset

• Solidworks plot:

• Excel Plot:

 

• Superimposed graphs plot

Animation:

https://youtu.be/aAygLXvMutY 

Conclusion: 

 So we were able to model the components of piston and make the assembly of it. Further we were able to plot the linear displacement graph for all the 3 different cases as well. The graphs gave an idea of how the linear displacement of piston takes place as it moves from TDC to BDC. When the piston pin is in the Centre of the piston, now when the piston reaches top or bottom dead Centre then, in this kind of setup the rod is straight up & down placing huge load on the rod. The crank has to rotate past TDC or BDC in order to get the piston moving again. This robs a lot of both power and RPMs from the engine.

Now with an offset pin, the piston wrist pin is a little offset to one side of the piston therefore the rod is not straight up and down when the piston is at TDC or BDC. This in turn allows the crank to rotate with much less resistance giving the engine more power and speed.

Having offset pin relieves the stress that is caused in the rod when it reaches top or bottom dead Centre. For the rod does not have to slam the piston up and then back down. The rod travels more in an arc.

Reference:

https://motocrossactionmag.com/amp/ask-the-mxperts-the-whys-and-wherefores-of-kawasaki-crank-offset/

https://benthamopen.com/contents/pdf/TOMEJ/TOMEJ-9-933.pdf

Drive Link:

https://drive.google.com/drive/folders/1s94KElWdPcXKA9bEMvyHOY3t7YLbBVv4