MBD Simulation on a Piston Assembly
Objective
To model piston assembly and to do the motion analysis to obtain the linear displacement of the piston head in three different cases.
Introduction
Piston assembly consists of the piston head, connecting rod, gudgeon pin, crank and crankpinThe piston is the part of an engine that reciprocates to produce power to rotate the crankshaft.
The way the piston moves, the amount of swept volume and thewrist pin offset plays an important role in the power produced inside an engine. In this Project, our concern will be limited to only the wrist pin offset.Wrist pin offset refers to the piston wrist pin being a bit offset to one side of the piston i.e. not exactly in the centre of the piston. Offsetting the cylinder axisfrom 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 and hence more powerIt also improves the noise characteristics of the engine due to piston slap at the top dead center (TDC)
Modeling of all the parts.
- Wrist pin
Motion Analysis
The motion analysis is carried out in three different conditions
Wrist Pin Offset - The position of the wrist pin is going to be varied as followed. But the center of the axis of the piston head and the crank are coincident to each other (i.e) They are on the same plane in all the three cases.For the second and third case the piston circle position is made offset 10mm positive and negative respectively.
"0" mm Offset -If the crank rotation is in the Clockwise direction
10 mm Positive Offset
10 mm Negative offset
Case 1:
Case 2:
Case 3:
Observation:
The amplitude varies for different cases.
Offsetting 10mm negative will make the crankshaft to put extra force to pull the piston from TDC to BDC.
The point in making offset is to increase the maximum displacement and angular velocity to be high in all cases. Stresses will be developed in wrist pin by offsetting
Result:
Linear displacement produced in different cases are :
- 0 mm offset - 302.708 mm
- 10 mm positive offset - 522 mm
- 10 mm negative offset - 302.521 mm