DESIGN AND MOTION ANALYSIS OF 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 centre 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.
3. Superimposing the three graphs in excel to compare the diagnostics of the cases.

SIMULATION CASES:

S. NO	WRIST PIN OFFSET	CRANK SPEED (RPM)
CASE 1	0mm	2000
CASE 2	10mm +ve	2000
CASE 3	10mm -ve	2000

PROCEDURE:

• Initially, 2D drawing of the Piston Assembly components is converted into a 3D model using Extruded Boss/Base command. The pictorial view of these models is given below.
• The Piston is designed with the aforementioned dimensions and a zero (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 design as per actual dimensions with zero tolerance.

• The End Cap is designed wrt 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 an assembly file with adequate mates’ specification.

ANIMATION:

CASE 1:

https://youtu.be/joaQ3wObiVs

CASE 2:

https://youtu.be/Nk86nsXh7JY

CASE 3:

https://youtu.be/1rhOPcGLCDs

RESULTS:

• CASE 1:

Geometry

Curve Obtained

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

Curve Obtained

The above plot depicts the slight difference in the extreme positions of the PISTON due to the non-linearity of the Wrist Pin and Crank axes.

• CASE 3:

Geometry

Curve Obtained

The plot obtained shows similar chaarcteristics to that of a Positive Wrist Pin Offset. The difference exists in the Crank angle at which the Piston reaches its Maximum or Minimum.

Superimposed Results:

LINK TO SOLIDWORKS PART AND ASSEMBLY FILES:

"https://drive.google.com/drive/folders/1sSia5pjl4HN13OFf32xl0ApMSNKNisJW?usp=sharing"

CONCLUSION:

The Motion Analysis of the Piston Assembly helps us to assess the working of a Slider-Crank Mechanism. Providing Offset offers much less resistance leading to more engine speed and power. It also helps to relieve the stress induced in case the Piston reaches the Top Dead Centre (TDC) and the Bottom Dead Centre (BDC).