MBD Simulation on a Piston Assembly

Motion analysis of piston assembly

Objective :

To perform the motion analysis on piston assembly in three different conditions as follows

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

Modeling of parts:

For the simulation of the piston assembly, we have to model the connecting rod, crank, piston, and wrist pin of the piston. To model the component all the values are taken with reference to lecture videos

For piston, the basic sketch is as follows in the front plane which is converted to the 3D component by revolving with respect to y-axis after that we sketch on right plane to create the cylinders and holes and fillets as shown in 3D piston component

For crank, we sketch on a front plane and get the model of half part of the crank by extruding the sketch and creating cylinders as there respective position as shown in 3D component so that we mirror the other half part

For the connecting rod, we extrude the sketch as shown to get the 3D component and sketch on the face of the thickness of semicircular part creates the cylinder and hole another half part of the connecting rod is created by using respective values of connecting rod also wrist pin is created by the respective dimension of holes in the piston

Creating assembly

To create the assembly

• we first assemble the crank and connecting rod by mating the pair in concentric and giving the distance of 1mm between the face of the connecting rod and internal face of the crank
• remaining part of the connecting rod is assembled with it so it has mating of concentricity with two holes and contact of faces
• connecting rod is then connected to wrist pin such that it is concentric with the hole and held at the central position of connecting by coinciding the central plane to each other
• now piston is assembled with the wrist pin by using concentricity with holes and coinciding the central plane to each other
• And to oscillate the piston in one plane we coincide the central plane of piston with the central plane of assembly and for other cases, we put the distance between these two planes respectively

Creating a study of motion :

• Firstly we create solid contacts with all the connected parts of the piston assembly
• We give the rotary motion of 2000 rpm to crank
• we use precise motion and perform the study at 7200fps to have more detailed and smoother output
• give the gravity the negative y-direction

Animation video : https://youtu.be/GRXGuhP5pnQ

Results :

for case 1

For case 2

For case 3

Superimposed chart :

Conclusion :

from the study, we can conclude that linear displacement remains same but in case 2 and case 3 with respect to time we see the values of displacement is nearly same or showing some difference with no offset this is happening because without offsetting the line of action of power transmission is caused impact load on the assembly which is harmful during operation. to get rid of this, offsetting the piston from crank so that the axis of the piston and connecting rod are aligned vertically at the moment of combustion - when the pressure in the cylinder is at its peak.

Due to the offset provided between the piston and crank the impact load is reduced. Doing this greatly reduces the stress acting on the connecting rod and friction from the diagonal force pushing the piston against the cylinder wall. At the same time, this enables more effective use of the energy produced by combustion which causes more efficient mechanisms in real-life applications.