MBD Simulation on a Piston Assembly (Multibody Dynamics using Solidworks)

Introduction

Piston motion analysis is the analysis of a piston and cranks assembly which consists of a piston head, wrist pin, connecting rod, end cap, and a crank.

Aim

Design the parts of a piston and crank assembly, assemble them and simulate their motion by restricting the degrees of freedom of every component so as to avail their motion in the required direction. A certain torque or angular velocity is provided to the crank and the motion of the piston is analyzed.

Parts

3D view of Piston's head in Solidworks

3D view of Wrist Pin in Solidworks

3D view of Connecting Rod in Solidworks

3D view of End Cap in Solidworks

3D view of Crank in Solidworks

3D view of Assembly in Solidworks

Motion Specification

1)Speed of rotation of the crank = 2000rpm

2)The wrist pin must be positioned as follows with respect to the plane of the axis of rotation of the crank.

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

3)Precise contact is enabled.

4)The crank is rotated for 1minute in the clockwise direction.

5)The frames per second are 12000.

6)"Contact" is enabled with Steel(dry) contact to every pair of contacts.

7)Gravity is enabled in the Y direction.

Motion Study

Case 1: Offset is 0mm.

Output: A plot of linear displacement with time

Case 2: Offset is 10mm.

Output: A plot of linear displacement with time

Case 3: Offset is -10mm.

Output: A plot of linear displacement with time

Observations and conclusions

• The displacement v/s time graph obtained is a smooth sinusoidal curve since the frames per second(fps) is high(12000).
• The maximum displacement of the piston without offset is slightly more than that with positive and negative of 10mm.
• In offset conditions, the load on the wrist pin is more than that in a 0 offset condition. This is because the crank has to rotate a larger angle to bring the piston downwards than when compared with 0 offset condition.