MBD Simulation on a Piston Assembly

AIM

MBD Simulation on a Piston Assembly

OBJECTIVES

• To create 3D models of all the parts(i.e. Piston, Gudgeon pin, Connecting Rod, Crank) and assemble them in SolidWorks.
• To carry out the motion analysis in three different conditions-

1. Wrist Pin offset- ‘0 mm’ and Crank Speed- 2000 RPM(clockwise)
2. Wrist Pin offset- ‘10 mm Positive’ and Crank Speed- 2000 RPM(clockwise)
3. Wrist Pin offset- ‘10 mm Negative’ and Crank Speed- 2000 RPM(clockwise)

• To plot the Linear Displacement of Piston Head in all three cases.

INTRODUCTION

Piston Assembly is an example of application of Slider-Crank Mechanism in which the Piston undergoes reciprocating motion and there is a conversion of Reciprocating to Rotating motion between the piston and Crank. The intermediate component connecting these two is the Connecting rod. The motion of the Connecting Rod is approximately Simple Harmonic Motion.

This simulation will result in the study of relative motion between the components and their effect on changing the position of particular element. The Motion Analysis of the Piston Assembly will be performed by giving input to the Crank in the form of Rotational motion and obtaining output from the displacement of Piston (reciprocating motion).

THEORY

This Assembly consists of the following parts-

1. Piston
2. Gudgeon pin or Wrist pin
3. Connecting Rod(divided into two parts)
4. Crank

Piston

A piston is a component of reciprocating engines located in the cylinder and is made gas-tight by piston rings. Its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via connecting rod. Piston reciprocates due the forces generated inside the combustion chamber. The piston is connected to the crank shaft through a connecting rod.

The Offset of 10 mm is provided in the model for Piston by varying the position of Hole for Gudgeon Pin

Positive Offset-’10 mm’

Negative Offset-’10 mm’

Gudgeon pin or Wrist pin

It is the part that connects the piston to the Connecting Rod. The piston is provided with a hole to accommodate the Gudgeon Pin. It also provides a bearing for the Connecting Rod to pivot upon as the piston moves.

Connecting Rod

A connecting rod connects the piston to the crank. This part is responsible for the conversion between rotational and reciprocating motion.

A connecting rod can rotate at both ends, so that the angle between the connecting rod and the piston can change as the rod moves up and down and rotates around the crankshaft

It usually consists of two parts i.e. the con rod and the end cap.The part that is to be connected to the crank is kept as a end cap. On placing the connecting rod and tightening the end cap, the big end of the connecting rod is ready to swivel about the crank pin.

Connecting Rod and End Cap-

Assembled Connecting Rod-

Crank

A crank is the final link that undergoes rotational motion. In case of multiple pistons and cranks, the cranks are mounted on a shaft called Crankshaft.

The Google Drive links for the Parts and Assemblies are given below-

Piston(without offset, with positive offset, with negative offset)-

https://drive.google.com/file/d/1nwpAII0zOCqz108j24GfOfzKzUq8ZPYj/view?usp=sharing

https://drive.google.com/file/d/1sZmttm3POg2nlOuJLP1kEyNF8uQtB2H_/view?usp=sharing

https://drive.google.com/file/d/1yGQj4zCNWtIRPmt2xXqvhEZMWkj7yDYl/view?usp=sharing

Gudgeon Pin-

https://drive.google.com/file/d/1A7D2gGIUSX2Fi1DVoo4fLrHCf7zPppvk/view?usp=sharing

Connecting Rod and End Cap-

https://drive.google.com/file/d/1oHqq2Yb7JIASnU1s1_cmj-LvKWJY-s6M/view?usp=sharing

https://drive.google.com/file/d/1k4eE-XmR5u74uBZKm_h28QH7sb3gX4oB/view?usp=sharing

Crank-

https://drive.google.com/file/d/1yUNVLDUQQiZXYi5BHDeO6tC0JDSUQivL/view?usp=sharing

Assembly-

https://drive.google.com/file/d/16ZXrTnvnVOa4WNPnoyTuCM1pv2V6peYy/view?usp=sharing

https://drive.google.com/file/d/12NTrbKdxv_eiEyzKn-RbVr_ktjTJBVMh/view?usp=sharing

https://drive.google.com/file/d/1EZFYDXFKQNShewonjIfwOY4MkG6Gar8K/view?usp=sharing

MOTION STUDY SETUP

• All the parts were individually modeled.
• The parts were assembled using the following Mates-

1. ‘Coincident’ mates of the Axis of Crank with the Right and Top Plane
2. ‘Distance ‘mate between face of Crank and Front Plane
3. ‘Coincident’ mates for corresponding surfaces and axes of Connecting Rod and End Cap .
4. ‘Coincident’ mate between axis of Crank pin and axis of big end of Connecting Rod.
5. ‘Distance’ mate for clearance between Connecting Rod and Crank.
6. ‘Coincident’ mates for constraining Gudgeon pin with Piston and Connecting Rod.
7. ‘Coincident ‘mate between Front Planes of Connecting Rod and Piston.

• Then ‘SOLIDWOKS Motion’ is enabled and the Motion Analysis is started
• The Crank is given rotation with the help of Rotary Motor by specifying 2000 RPM.
• ‘Contact ‘option was used to provide Solid Body Contacts between the pairs of parts i.e. Piston-Gudgeon Pin, Gudgeon pin-Connecting Rod, Connecting Rod-Crank and the Material was selected as ‘Steel(Dry)’
• ‘Gravity’ is enabled in the negative Y direction.
• In the ‘Motion Study Properties’, the Frames per second was chosen to 12000.(as for 2000 RPM=2000*6=12000 deg/sec;so, for accurate value for each position)
• The ‘Calculate’ option was used.
• Then the required plot of Linear Displacement of Piston Head was obtained.
• The same procedure was repeated for simulation for Positive and Negative offset by changing the Piston(by ‘Replace Entities’ option)

RESULTS

Linear Displacement of Piston Head without Offset

Linear Displacement of Piston Head with Positive Offset

Linear Displacement of Piston Head with Negative Offset

Linear Displacement of Piston Head

OBSERVATIONS & EXPLANATION

1. From the Results we can observe that there is not much change in Magnitude of Linear Displacement of Piston Head(difference between crest and trough) by offsetting the Wrist pin.
2. At a given point of time , the Linear Displacement follows the following order-

• Upward Stroke(BDC to TDC) : Negative offset > Zero Offset > Positive Offset
• Downward Stroke(TDC to BDC) : Positive offset > Zero Offset > Negative Offset

3. It is noticed from the superimposed plot that for a given period of time, the frequency follows the order- Negative offset > Zero Offset > Positive Offset

CONCLUSION

So, the Motion Analysis of Piston Assembly was studied and successfully completed.