MBD SIMULATION ON A PISTON ASSEMBLY

AIM: Design and motion analysis of an IC ENGINE PISTON ASSEMBLY

INTRODUCTION:

A slider-crank linkage is a four-link mechanism with three revolute joints and one prismatic, or sliding, joint. The rotation of the crank drives the linear movement the slider, or the expansion of gases against a sliding piston in a cylinder can drive the rotation of the crank.

There are two types of slider-cranks: in-line and offset.

1. In-line: An in-line slider-crank has its slider positioned so the line of travel of the hinged joint of the slider passes through the base joint of the crank. This creates a symmetric slider movement back and forth as the crank rotates.
2. Offset: If the line of travel of the hinged joint of the slider does not pass through the base pivot of the crank, the slider movement is not symmetric. It moves faster in one direction than the other. This is called a quick-return mechanism.

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.

OBJECTIVE:

1. Performing Motion analysis of the piston assembly in No offset, positive offset and Negative offset condition of the piston.
2. Obtaining Plots for Linear Displacement of the piston head in the three cases mentioned.

SIMULATION CASES: -

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

PROCEDURE:

Initially, 2D drawing of the Piston Assembly components is converted a 3D model using Extruded Boss/Base command.

It is designed with the mentioned dimensions and 0 wrist pin offset.

To connect the piston and the connecting rod, a wrist pin is designed with justified dimensions.

It is followed by the Connecting Rod as per th actual dimensions with zero tolerance.

The end cap is designed w.r.t the connecting rod end in order to have a proper fit.

To transmit the motion from connecting rod, a crank is designed with shaft size in accordance with that of the end cap and the connecting rod.

Now, assemble the parts in assembly file with proper mates specification.

Animation:

CASE 1:

CASE 2:

CASE 3:

RESULTS:

Case 1-

Geometry-

Plot-

The Displacement vs Crank angle shows a to and fro motion of the Piston. The values are consistent with that of an ideal solution.

Case 2-

Geometry-

Plot-

The plot depicts the slight difference in the extreme positions of the piston due to non-linearity of the wrist pin and the crank axes.

Case 3-

Geometry-

Plot-

The plot obtained shows similar characteristics to that of a positive wrist pin offset. The difference exists in the Crank angle at which the piston reaches its minimum or maximum.

Superimposed results:

CONCLUSION: The motion analysis of the piston assembly helps us to assess the working of a slider-crank, mechanism. Plots are obtained at different offset positions.