MBD Simulation on a Piston Assembly

Aim:

To model components of IC Engine Piston Assembly and plot graph of Linear Displacement of Piston in the given three cases:

a) "0" mm Offset of Gudgeon pin

b) "10" mm Positive Offset of Gudgeon pin

c) "10" mm Negative Offset of Gudgeon pin

Introduction:

Engine:
An engine or motor is a machine designed to convert one form of energy into mechanical energy. Heat Engines, like the internal combusstion energy, burn a fuel to create heat which is then used to do work.

Given below is the working of an IC Engine followed by the Piston Assembly:

Piston Assembly:

Following are the parts required in an Piston Assembly:

• Piston
  
  
• Wrist pin/Gudgeon Pin
  
• Connecting rod
  
  
• Crankshaft
  
  
• End cap

* 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.

* Wrist Pin/Gudgeon Pin:
In internal combustion engines, the gudgeon pin connects the piston to the connecting rod, and provides a bearing for the connecting rod to pivot upon as the piston moves.

* 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.

* Crankshaft:
A crankshaft is a rotating shaft which (in conjunction with the connecting rods) converts reciprocating motion of the pistons into rotational motion.

* End Cap:
End cap joins with the connecting rod to hold the crankshaft and help in it's rotation.

Procedure:

1. Model Design:
Includes making the cad model of the system that is to be analyzed.

2. Assembly:
With the help of mates parts are combined to form an Assembly.

3. Applying Set-Up:
Includes setting up the motor, contacts and material.

4. Motion Analysis:
The solver is run giving out the results for plots including forces,velocities,accelerations and identifying the minimum and maximum values of those to determine the critical regions.

Case Study:

1. Model Design:

i. Piston:
First we start with the modelling of piston. It is done for all three cases as only piston varies in all three cases.

* Case 1:

Fig 1: Piston with 0 mm Offset

* Case 2:

Fig 2: Piston with 10 mm Positive Offset

* Case 3:

Fig 3: Piston with 10 mm Negative Offset

ii. Connecting Rod:
Now we go on to build Connecting rod.

Fig 4: 3D of Connecting Rod

iii. Gudgeon Pin/Wrist Pin:
Next we model the wrist pin.

Fig 5: 3D model of Wrist pin

iv. Crank:
Now we go on to model the crank.

Fig 6 : 3D model of the crank

v. End Cap:
Lastly, we model the end cap.

Fig 7 : 3D model of End cap

2. Assembly:
Now we go on to the Assembly section. Here first we import the parts and assemble them with the help of essential mates.

i. Case 1:

Fig 8: Assembly with 0 mm Offset

ii. Case 2:

Fig 9: Assembly with 10 mm Positive Offset

iii. Case 3:

Fig 10: Assembly with 10 mm Negative Offset

3. Applying Set-Up:

The Set-Up done for all the three cases is same. The set-up is shown below:

• In Motor Option, 2000 RPM is applied to the centre axis of Crank.
• Apply Gravity in the Y-axis.
• In Motion Study Properties, select 7200 FPS and enable Precise Contact.
• Apply contacts between:
  i. Crank and End Cap.
  ii. Connecting rod and Crank.
  iii. Connecting rod and Wrist pin.
  iv. Wrist pin and Piston.
  Apply Steel(Dry) as material for all.

Fig 11: Applied Set-up

4. Motion Analysis:

Following are the results for all the 3 cases:

* Case 1:

Fig 12: Linear Displacement Plot for 0 mm Offset

* Case 2:

Fig 13: Linear Displacement Plot for 10 mm Positive Offset

* Case 3:

Fig 14: Linear Displacement Plot for 10 mm Negative Offset

Observation:

The below image shows combination of all the three plots:

Fig 15: Superimposition of All Linear Displacement Plots

Since there are overlaps appearing but a very minute level a close up view is shown below:

Fig 16: Close-up view of Superimposition of All Linear Displacement Plots

Conclusion:

• In Case 1, "0" mm offset the top position of the piston is at 302 mm and bottom position at 203 mm. Thus, the total piston displacement is 99 mm.
• In Case 2, "10" mm positive offset the top position of the piston is at 302 mm and bottom position at 202 mm. Thus, the total piston displacement is 100 mm.
• In Case 3, "10" mm negative offset the top position of the piston is at 302 mm and bottom position at 202 mm. Thus, the total piston displacement is 100 mm.
• So, by observing all the results it shows that when there is "0" mm offset the stroke length is 99 mm but when in case of "10" mm positive & negative offset the stroke length changes to 100 mm.
• Hence, it is proved that offseting of piston pin does affect the stroke length of the piston as the engine runs quieter and produces more horsepower due to lower friction during the combustion process.