MBD Simulation on a Piston Assembly

Motion analysis of piston crank assembly using solidworks

Aim

To create 3D models of engine parts and carry out motion analysis for different wrist pin offset conditions.

Introduction

Piston crank assembly

The piston and the crank are connected through the connecting rod. The reciprocating motion of the piston is converted to rotational motion of the crank and vice versa. The fundamental mechanism behind this arrangement is slider crank mechanism. This type of arrangement is used in IC engines, gas compressors and reciprocating pumps.

3D CAD models

Case 1: 0mm wrist pin offset (2000 RPM)

Plot 1

Case 2: 10mm positive offset (2000 RPM)

Plot 2

Case 3:10mm negative offset (2000RPM)

Plot 3

Super imposed plot

Results and discussions

1. The linear displacement of the piston in all the conditions is almost similar but the maximum linear displacement is achieved in the 0mm offset condition.
2. Maximum linear displacement order- 0mm offset>10mm positive offset> 10mm negative offset
3. It is observed that when the wrist pin is at the centre of the piston (0mm offset) and as the piston reciprocates inside the cylinder blocks the connecting rod is moves straight up and down and this increases the load and stress on the connecting rod. Thus the power and in turn the overall efficiency of the engine is reduced.
4. It is observed that when the wrist pin is at an offset of 10mm (positive or negative) and in this case as the piston reciprocates, the connecting rod does not move straight up and down and thus it rotates at much lesser resistance which in turn increases the power and efficiency of the engine.

Animation of the piston crank assembly