MBD Simulation on a Piston Assembly

Aim: MBD Simulation on a Piston Assembly. Model all the parts and then assemble them in SolidWorks. The motion analysis is going to be carried out in three different conditions,

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

Obtain the Linear displacement of the Piston Head in all the three cases. Then export the graphs into Excel. Then Superimpose all the three graphs into a single graph.

Introduction : let’s talk about the different parts.

Piston Head :

The piston head is the top surface (closest to the cylinder head) of the piston which is subjected to tremendous forces and heat during normal engine operation. A piston pin bore is a through hole in the side of the piston perpendicular to piston travel that receives the piston pin.

Piston pin :

Piston pin is a connecting link between piston and connecting rod. It looks like a simple cylindrical shaft ,can be solid or hollow. At ends , it has a chamfer. The piston pin is held in the piston by circlips, while from the middle portion it is surrounded by the connecting rod smaller bore end.

Connecting Rod :

A connecting rod, also called a con rod, is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the crankshaft. The connecting rod is required to transmit the compressive and tensile forces from the piston, and rotate at both ends.

The predecessor to the connecting rod is a mechanic linkage used by water mills to convert rotating motion of the water wheel into reciprocating motion.

The most common usage of connecting rods is in internal combustion engines or on steam engines.

End Cap:

End cap is connected to the end of the connecting rod, which is assembled crank.

Crank :

Almost all reciprocating engines use cranks (with connecting rods) to transform the back-and-forth motion of the pistons into rotary motion.

Basic theory on the motion study:

motion study as the “Science of eliminating wastefulness resulting from ill-directed and inefficient motions”. The main aim of motion study is to find the scheme of least wastage of labour. Subsequently, the scope of Motion Study was enlarged and it was named as Method Study.

Ready your every parts and assemble them.

Switching to SolidWorks Motion Manager Switch to SolidWorks Motion by clicking the motion analysis tab in the bottom left hand corner.

SolidWorks Assembly Mates.

Specifying the Input Motion and

Under Motor Type selet Rotary Motor. In our case i have used 2000 rpm constant motor

Select contact between parts. Between crank-end cap,crank-con rod,con rod-piston pin,piston pin and piston head.

Go to settings and set frames per seconds as per our requirements. I have used 12000 as per calculation.

Select Simulation time.i have choosed 1 sec

Running the Simulation.

Looking at the Results. And select plots as per our requirements.

Let’s go through one by one,

Model Description :

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.

"0" mm Offset :

Linear Displacement Plot For Piston head:

10 mm Positive Offset - If the crank rotation is in the Clockwise direction.

Linear Displacement plot for piston head:

10 mm Negative Offset - If the crank rotation is in the Clockwise direction.

Linear Displacement plot for piston head:

Results and Conclusion:

Superimposed Plot of all three plots:

• The linear displacement graph is smooth for all the 3 cases.
• When there isn't any offset the piston dispalcement will be maximum than the offset conditions as there is slight reduction in the piston displacement which is obvious since the piston has to travel a bit less distance because of offsetting because the conneting rod will not be straight at TDC and BDC because of 10mm offset.
• When the piston pin is in the centre of the piston, now when the piston reaches top or bottom dead centre then, in this kind of setup the rod is straight up & down placing huge load on the rod. The crank has to rotate past TDC or BDC in order to get the piston moving again. This robs a lot of both power and RPMs from the engine. This results in piston slap.
• Now with an offset pin, the piston wrist pin is a little offset to one side of the piston therefore the rod is not straight up and down when the piston is at TDC or BDC. This in turn allows the crank to rotate with much less resistance giving the engine more power and speed.
• This will result in reduction of stresses generated in the connecting rod and less piston slap can be reduced using this.
• Animation Link of assembly at zero offset of Wrist pin : https://youtu.be/PhEUDG7hVyA