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 crankpin
The 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 the wrist 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 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 and hence more power
It also improves the noise characteristics of the engine due to piston slap at the top dead center (TDC).

In this project we will study following three cases:

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

Modeling of parts:-

Piston:

Crank:

Connecting rod End cap:

Connecting rod:

Wrist pin:

The motion study :

Following mates are done on assembly:

1. Crank can rotates only about its axis.

2. Piston can move linearly.

3. Connecting rod can rotate to transmit power.

In the Motion study the following steps are performed.

1. Select motion analysis in the drop down menu.
2. Motor is given to crank with the speed 2000 RPM.
3. Frames per second is given as 2000*6=12000 with precise contact.
4. Contact is given between end pin and crank, crank and connecting rod, connecting rod and wrist pin and wrist pin and piston. Material selected for each case is steel (Dry).
5. Gravith in the Y direction.

Study is done for following three cases-

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

1. "0" mm Offset:-

Linear displacement of the Piston Head:

2. Wrist pin offset 10 mm Positive:

Linear displacement of the Piston Head:

3. Wrist pin offset 10 mm Negative:

Linear displacement of the Piston Head:

Animation:-

Results and explanation:-

The displacement for 0mm offset is minimum and displacement for 10mm positive offset is maximum.