MBD Simulation on a Piston Assembly

Aim: To perform motion analysis on Piston Assembly

Objective:

The main objective is to design different parts of piston assembly, assemble them and then perform motion analysis on it for following cases.

Sr. No.	Wrist Pin Offsert	Crank Speed (RPM)
1	0 mm	2000
2	10 mm Positive	2000
3	10 mm Negative	2000

Theory:

The piston assembly consists of piston head, Gudgeon pin (or wrist pin), connecting rod, end cap and crank. It is used to convert reciprocating motion of piston into rotary motion of crank and vice versa. The parts modelled in Solidworks are shown below,

1. Piston Head

2. Gudgeon pin ( Wrist pin)

3. Connecting Rod

4. End Cap

5. Crank

Piston Assembly:

Motion Analysis:

For performing motion analysis motor is applied to the crank with 2000RPM in clockwise direction and contacts is defined between all mating bodies.

For capturing each frame in analysis a frame rate of 12000 FPS is used with precise contact.

The results for different cases are as shown below:

Case 1: 0 mm Offest

Case 2 : 10mm Positive Offset

Case 3 : 10mm Negative Offset

Results superimposed for all three cases:

Conclusion:

From the results, it can be seen that with offset and without offset there is no difference between the piston displacement but there is a difference in frame when the piston reaches top dead center. It can be seen that the curve peaks locations are different. This shows that the piston reaches top dead centre at different crank angle.

With 10mm positive offset, the curve peak is located at slightly right to the no offset curve that means the crank has to move by a slightly larger angle than no offset condition so that piston reaches top dead centre.

With 10mm Negative offset the situation is opposite, the curve peak is located at slightly left to the no offset curve that means the crank has to move by a slightly smaller angle than no offset condition so that piston reaches top dead centre.

It can also be concluded that with no offset condition when piston is at top dead centre than connecting rod is held vertical but when offset is present then the connecting rod is not vertical, it is at an angle with the vertical axis and obliquity of the connecting rod reduces the effort required to push it and thus results increased power output from the engine.