MBD Simulation on a Piston Assembly

Aim:

The aim of the piston assembly is to simulate the engine components with different offset conditions of the wrist pin and also to influence the offset condition on the displacement of the piston.

Introduction:

Modeling the 3D parts:

All the models are sketched with respect to the front plane to make it easy for the assembly. The dimension is taken from the Piston assembly video.

Piston: A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod.

Gudgeon Pin (Wrist pin): the gudgeon pin connects the piston to the connecting rod and provides a bearing for the connecting rod to pivot upon as the piston moves. In very early engine designs the gudgeon pin is located in a sliding crosshead that connects to the piston via a rod.

Connecting rod: A connecting rod is a rigid member which connects a piston to a crank or crankshaft in a reciprocating engine. Together with the crank, it forms a simple mechanism that converts reciprocating motion into rotating motion.The connecting rod is locked to the crank with an end cap.

Crank: it Is a mechanical part able to convert the reciprocating motion from the piston into rotational motion.

Final Assembly:

the 3D parts modeled are assembled together according to motion constraints and they are checked for the desired motion manually before moving to the motion analysis

Motion study:

Before moving to the motion analysis, the desired steps are taken down:

1. The desired contact pairs are assigned and the material we assumed is Dry steel.
2. The motor with 2000 rpm is assigned to the crank axis.
3. The frames per second are made to be 7200 and the precise contact is used.
4. Gravity is assigned along the Y-axis for getting much more exact values.

All three cases are done at 2000 rpm clockwise rotation and 7200 fps with precision contact.

The calculation is performed for the motion analysis for about 1 sec. The linear displacement of the piston head w.r.t time is obtained.

The motion analysis is done upon 3 cases:

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.

CASE 1: Zero offset of the wrist pin

Linear Displacement:

CASE 2: +10 mm offset of the wrist pin

Linear Displacement:

CASE 3: -10 mm offset of the wrist pin

Linear Displacement for Case 3:

Superimposed graph:

this graph is plotted to know the behavior of the displacement vs time curve for different offset conditions.

Result and Explanation:

1. The amplitude varies for different wrist pin configuration.
2. The offset affects the linear displacement of the piston against time.
3. Comparing the plots, the positive offset and zero offsets don’t vary much by time and they follow almost the same distribution on the plot.
4. While in the negative offset, the displacement of the piston takes more time than Zero offset one.

Primarily, The piston offset is used to offset the piston from the engine axis so that the whole weight of the connecting rod and piston head doesn’t fall on the crank. also the reduce the stress-induced during the power stroke.

The Link for the animation of piston assembly is given :

Piston Assmebly

Also, the google drive link for the Solidworks parts and assembly is given:

Piston assembly parts