MBD Simulation on a piston assembly
Objective
To model piston assembly and do motion analysis for different wrist pin offset.
Theory
Piston is a part of the engine which reciprocates back and forth and convert linear motion into circular motion. Piston assembly includes piston, connecting rod, crank, crankpin and gudgeon pin. Wrist pin offset refers to the space between the plane in which piston moves and the plane on which crank axis lies parallel to direction of piston. Wrist pin offset is given to reduce noise of the engine due to piston slapping and to improve engine output by reducing friction loss in the engine.Offsetting the cylinder axis from the crankshaft axis, minimizes rod angularity when cylinder pressure is at its highest. Reduced angularity leads to lower piston thrust forces, hence lower frictional losses during the period of maximum cylinder pressure.
Modelling: Piston, connecting rod, crank, crankpin and gudgeon pin are modelled in solidworks.
Motion Analysis
The motion analysis is going to be carried out in three different conditions,
| Sl.No |
Wrist Pin Offset ` |
Crank Speed (Rpm) |
| 1 | \"0\" mm | 2000 |
| 2 | 10 mm Positive | 2000 |
| 3 | 10 mm Negative | 2000 |
Observations
1. Wrist pin offset = 0 mm
Maximum height reached by piston is 310.95 mm.
2. Wrist pin offset = 10mm positive
Maximum height reached by piston is 310.92 mm.
3. Wrist pin offset = 10mm negative
Maximum height reached by piston is 310.93mm.
Comparision.
The distance travelled by piston is a bit phased out with other cases.
Result
Maximum height reached by piston for
- 0mm offset = 310.95mm
- 10mm positive offset = 310.92mm
- 10mm negative offset = 310.93mm
Conclusion: Giving offset to the wrist pin decreases the distance travelled by the piston more in positive offset than negative offset. This reduces the piston slapping and also reduces the friction loss thus increasing power output of the engine.