MBD Simulation on a Piston Assembly

AIM:

To model a crank, connecting rod, piston head and a pin, assemble them, and then create a motion study while changing the relative position of the crank head with respect to the shaft and then plot the linear displacement of the piston with respect to time.

INTRODUCTION:

In this motion study, we will assemble the parts, study the motion analysis of a piston assembly. We have to be careful while doing it and make the allignment properly such that, the motion occurs only in the way we want it to which can be checked by trying tto pull/drag out the parts of the assembly. If they still stick together, we know that the assembly is done correctly. We have to also make sure that the parts are properly positioned. If the parts are dragging, the motion might get a little messy. All these steps can be done with proper mate tools.

The simulation was carried out in the following conditions:

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

MODELLING AND ASSEMBLY:

The simulation of the whole system required the following parts:

connecting rod:

Its the part that connects the piston to the crank shaft. In a way, it helps in transforming the linear motion of the piston into rotational motion of the crankshaft. Its connected to the crank shaft and the piston head in such a way that rotational motion is possible between either of the parts.

crank:

Its the other end to which the connecting rod is connected to. It acts as the output to the linear motion of the psiton, which is infact caused by the fuel energy. Its motion causes the wheels to function and rotate.

end cap:

It acts as a holding structure for the connecting rod to hold onto the crank shaft. The connecting rod and end cap together form a structure to connect with the crank shaft.

wrist pin:

It connects the piston to the connecting rod. The pin acts as a pivot between the connecting rod and the piston, restricting any unneccesary movements.

piston:

It is a cylindrical part that faces the force of combustion of the fuel and results in repeated linear motion. It is connected to the connecting rod and in fact its linear motion is further transformed into rotational motion by the crankshaft.

ASEMBLY:

The assembly of the setup was carried out with the help of assembly mates like coincident and concenteric mates. The crank shaft was assembled in such a way that its roation is possible in only dimension. This configuraton along with linear movement of the piston completes the configuration of the piston assembly.

To begin the motion study, a rotatory motor was applied to the crank shaft and the solid contact was applied between the part files and then gravity was added along the Y- direction.

In the settings tab, precise contact was enabled and then, the FPS was set top 12000, since we need one frame per degree and we have set the motor speed at 2000 RPM.

OBSERVATION:

After modelling and the assembly of the parts, the simulation was run with three cases:

CASE-1(0 offset)-

The piston axis and the crankshaft axis are completely vertical to one another.

PLOT:

CASE-2(+10 mm offset)-

PLOT:

CASE-3(-10 mm offset)-

PLOT:

SUPERIMPOSED PLOT:

YOUTUBE LINK FOR THE ANIMATION:

https://www.youtube.com/watch?v=jag2Foyos2M&feature=youtu.be

OBSERVATION AND CONCLUSION:

After observing the plot, we can observe that offsetting the axis of the pistoin and the crankshaft result in a slight change in the amplitude of the displacement. Hence, we can adjust the offset of the piston to maximize our output.