MBD Simulation on a Piston Assembly

SIMULATION OF PISTON ASSEMBLY USING SolidWorks

1. AIM : To analyse the motion study of Piston Assembly using SolidWorks.

2. OBJECTIVE :

• To create 3D models of all the parts required in Piston Assembly.
  1. Crank
  2. Connecting Rod
  3. End Cap
  4. Piston Head
  5. Wrist Pin

• To perform motion analysis by rotating Crank at a constant speed of 2000 rpm.
• To do motion analysis for the three different conditions,

Sl. No	Wrist Pin Offset	Crank Speed (Rpm)
1	“0” mm	2000
2	10 mm Positive	2000
3	10 mm Negative	2000

• To obtain the Linear Displacement of the Piston Head in all the three cases.
• To plot the obtained linear displacement graph into Excel.
• To Superimpose all the three graphs of linear displacement into a single graph.

3. INTRODUCTION :

3.1 PISTON :- A piston is a component of reciprocating engines, reciprocating pumps, gas compressor 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.

fig.1: Parts of the Piston

3.2 Piston Head :- The piston head is the top surface (closest to the cylinder head) of the piston which is subjected to tremendous forces and heat during normal engine operation. A piston pin bore is a through hole in the side of the piston perpendicular to piston travel that receives the piston pin.

3.3 Piston Ring :- Located between the cylinder and the piston, piston rings are necessary components that allow the engine to operate efficiently. Piston rings have four major functions-

1. Compression gas sealing
2. Lubricating oil film control
3. Heat transfer
4. Support piston in the cylinder

3.4 Wrist Pin :- In internal combustion engines, the wrist pin connects the piston to the connecting rod, and provides a bearing for the connecting rod to pivot upon as the piston moves.

• Wrist pin is also known as Gudgeon pin or, Piston pin.

3.4.1 Wrist Pin Offset : The position of the wrist pin is going to be varied as followed. But the center of the axis of the piston head and the crank are coincident to each other (i.e) They are on the same plane in all the three cases (“0”mm offset, 10mm positive offset, and 10mm negative offset).

“0” mm Offset - Centre point of piston head is directly above or, perpendicular to the centre point of crank.

10 mm Positive Offset – If the crank rotation is in the Clockwise direction then,

10 mm Negative Offset – If the crank rotation is in the Clockwise direction then,

3.5 Connecting Rod :- A connecting rod, also called a con rod, is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the crankshaft. The connecting rod is required to transmit the compressive and tensile forces from the piston, and rotate at both ends.

The predecessor to the connecting rod is a mechanic linkage used by water mills to convert rotating motion of the water wheel into reciprocating motion.

The most common usage of connecting rods is in internal combustion engine or on steam engines.

3.6 Crankshaft :- The crankshaft, sometimes casually called the crank, is the part of an engine which changes the up and down motion of the pistons into rotation.

4. PROCEDURE :

For performing motion analysis of our Piston assembly, we will need 3D model of assembly of the Piston.

So, first we need to design 3D model of following-

1. Crank
2. Connecting Rod
3. End Cap
4. Piston Head
5. Gudgeon Pin

And for designing any 3D model, we have to design 2D sketch of the model first, after that we can proceed for designing 3D models.

• All the dimensions are in the unit system of MMGS (i.e. millimeter, gram, second).
• Front plane is used for 2D sketch of all parts.

5. 3D MODELS :

Crank

End Cap

Connecting Rod

Piston Head

Gudgeon Pin

Assembly Desing :

For performing assembly, we need to import the 3D model of parts which have to be assembled; here those model parts are as follows -

Part or, Model	Quantity
Crank	1
End Cap	1
Connecting Rod	1
Piston Head	1
Gudgeon Pin	1

fig.2 Piston Assembly

Motion Study :

• Motion study can be done in SolidWorks by using ‘Motion Analysis’ under ‘SolidWorks Motion’ option from ‘SolidWorks Add-Ins’ .

So, we are going to choose the ‘SolidWorks motion’ option from ‘SolidWorks Add-Ins’ and then going to ‘Motion Analysis’ option which we can find below in the SolidWorks window.

6. BODY OF CONTENT :-

First make sure that none of the part or model is fixed, because every part of piston assembly goes under some type of motion while working.

6.1 Study-1 (Motion Analysis for “0” mm Wrist Pin Offset)

For this, first going to make right plane of piston head coincident with the right plane of assembly as,

Then, going to set up the motor at the center axis of crank at a constant speed of 2000 rpm. And assigning the rotation of the motor as clockwise direction as,

Setting up time frame for our motion study to 5 seconds.

After that going to assign solid body contact by selecting contact option for all the parts by selecting two parts at a time which are going to be in contact. There we can also assign material to the models. So, selecting ‘Steel (Dry)’ material for all the parts.

Now, setting up the number of frames per second equal to 7200 frames per second and also selecting precise contact for better visualization.

We will also provide gravity in Y direction (i.e. towards downward).

Now we will calculate the motion study and then selecting the top face of piston head for calculating the linear displacement of the piston head.

• Simulation is runned for 0.3 second (it is going to follow same repetitive motion further).

Now, we will get the plot for linear displacement by clicking on result and plot section as -

fig.3: Linear_Displacement Vs Time plot of Piston Head ("0" mm Offset)

6.2 Study-2 (Motion Analysis for 10 mm Positive Wrist Pin Offset)

For this we will follow the same process as performed in our above study with a few changes in that, which are as follows -

Modifying the coincident relation of right plane of crank and assembly with a distance of 10mm as shown below,

Now we will calculate the motion study and then selecting the top face of piston head for calculating the linear displacement of the piston head. After that, we will get the plot for linear displacement by clicking on result and plot section as -

fig.4: Linear_Displacement Vs Time plot of Piston Head (10 mm Positive Offset)

6.3 Study-3 (Motion Analysis for 10 mm Negative Wrist Pin Offset)

For this we will follow the same process as performed in our above study with a few changes in that, which are as follows -

Modifying the distance relation of 10mm between right plane of crank and assembly with a negative distance of 10mm as shown below,

Now we will calculate the motion study and then selecting the top face of piston head for calculating the linear displacement of the piston head. After that, we will get the plot for linear displacement by clicking on result and plot section as –

fig.5: Linear_Displacement Vs Time plot of Piston Head (10 mm Negative Offset)

7. RESULTS :

Study-1 (Motion Analysis for “0” mm Wrist Pin Offset)

>>Linear Displacement of piston head at “0” mm Wrist pin offset

Study-2 (Motion Analysis for 10 mm Positive Wrist Pin Offset)

>>Linear Displacement of piston head at “10” mm Positive Wrist pin offset

Study-3 (Motion Analysis for 10 mm Negative Wrist Pin Offset)

>>Linear Displacement of piston head at “10” mm Negative Wrist pin offset

SUPERIMPOSE ALL THE THREE GRAPHS :-

As we can see from the linear displacement plots for all three cases that, all the plots are very much similar to each other. So, for comparing the results of three cases, we are going to use superimposed graph for all three graphs. By doing this, we can plot all the graphs in a single graph which will help us to understand the difference between the plots in better way. The superimposed graph for the three graph is as below,

>>Linear Displacement of piston head

More Detailed view of superimposed graph –

Link for Results, 3D models, spreadsheet, animation :-

https://drive.google.com/file/d/1eNLRJZCkJbBjquvQQLuaMrvFF7mP4Djq/view?usp=sharing

Animation of Piston Assembly :-