MBD Simulation on a Piston Assembly
AIM: Study Motion Analysis Of Piston Assembly in SolidWorks
OBJECTIVES:
- Design & Assembly of Parts for Piston assembly.
- Run & analyze Motion analysis.
- Compare the plots of Linear displacement Vs Time for Piston head in following cases for the same crank speed of 2000 RPM:
- Wrist pin offset = 0 mm
- Wrist pin offset = 10 mm Positive
- Wrist pin offset = 10 mm Negative
BODY OF CONTENT:
Introduction:
Piston cylinder assembly is the main component of the engine wheather it is CI OR SI. Combustion takes place inside the cylinder which is responsible for the motion of the connecting rod. Connecting rod is connected with the piston with a pin called gudgeon pin or wrist pin. Other end is connected with the crank with end cap. This translation motion of connecting rod is converted to rotational motion of the output shaft by crank.
There are basically four stroke per cycle in four stroke engine & two stroke per cycle in two stroke engine.
Assembly consists mainly following parts:
PISTON:
CONNECTING ROD:
END CAP:
GUDGEON PIN:
CRANK:
Now go to the assembly & assemble all parts such that they have desired relative motion.
Now go to the motion study & select the motion analysis from the list.
As discussed we have to consider three case:
- CASE-01
Crank Pin having '0' mm offset. (As shown in figure)
Apply rotary motor of 2000 RPM to the crank.
Apply solid body contact to the parts having contact each other. And apply gravity.
Now run the motion analysis at 7200 fps. And record the motion.
Now generate the plot of linear displacement of piston Vs time.
Now export it to spreadsheet & generate the plot.
One can see from the plot that the piston displacement is of around 80 mm.
- CASE-02
Crank pin having 10 mm positive offset. (As shown in figure)
Now duplicate the motion study. Change the piston part having 10 mm positive offset & apply suitable mates.
Follow the same procedure & generate the plot.
Now export it to spreadsheet & generate the plot.
One can see from the plot that the piston displacement is of around 80 mm.
- CASE-03
Crank pin having 10 mm Negative offset. (As shown in figure)
Now duplicate the motion study. Change the piston part having 10 mm Negative offset & apply suitable mates.
Follow the same procedure & generate the plot.
Now export it to spreadsheet & generate the plot.
One can see from the plot that the piston displacement is same as the previous one of around 80 mm.
RESULT & CONCLUSION:
Now merg all the plots in excel to compare all three cases.
As one can see from the plot comparision all the three cases have the same displacement value over the cycle for the same input.
It can be shown that piston displacement is independent of the wrist pin offset. It has no effect on the result.
First case is slightly different than the other two for some time but after that it is also synchronize with them.
Hence, one can conclude that offset has slight or no effect on piston displacement.