MBD Simulation on a Piston Assembly
Aim: Multibody Dynamic study Simulation on a Piston-crank Assembly.
Objective:
To design the parts of piston-Crank Assembly and study its motion by generating graphs of linear displacement of Piston at 2000 RPM with precise contacts in 3 different conditions.
Piston motion analysis:
Piston motion analysis is the study of the reciprocating motion of the piston in the cylinder and the motion of the assembly attached i.e. connecting rod, end cap, crankshaft & wrist pin. First of all, for the assembly of a connecting rod, crankshaft, end cap, wrist pin and the piston itself, we will prepare the geometric model of all the necessary components.
we have designed the following parts:
- Piston Head
- Gudgeon Pin (Wrist pin)
- Connecting rod
- End Cap
- Crank
After that, they are assembled using suitable constraints.
The geometry of the parts:
Piston: It 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.
Connecting rod: Drawing two sets of two concentric circles at some distance and then joining them with a line than giving fillet to it then use the extrude option and use extrude cut to remove unwanted part of connecting rod then using extrude and extrude cut we will prepare the bolting area.
End Cap: End cap is connected to the end of the connecting rod, which is assembled crank.
Crankshaft: Is a mechanical part able to convert the reciprocating motion from the piston into rotational motion.
Gudgeon Pin (Wrist pin): Drawing a circle and then using extrude option and then giving chamfer to each end.
Final assembly: The piston, connecting rod, wrist pin, end cap and the crank are assembled as shown below using assembly mate option. First, the crank is made coincident with the assembly planes so that it can rotate about its axis and then connecting rod and end cap assembly is made coincident with the crank axis. The wrist pin is made coincident with the piston and with its front plane and it is then assembled to the connecting rod. This will result in the required assembly for the motion analysis.
Motion Study Analysis
The motion study: In the Motion study the following steps are performed.
- Select motion analysis in the drop-down menu.
- The motor is given to crank with the speed 2000 RPM.
- Frames per second are given as 12000 with precise contact.
- Contact is given between endpin and crank, crank and connecting rod, connecting rod and wrist pin and wrist pin and piston. The material selected for each case is steel (Dry).
- Gravity in the Y direction.
The calculations are performed for the motion analysis for about 3 sec. The linear displacement of the piston w.r.t time is obtained.
Case 1: Motion Analysis for "0" mm Offset
Motion analysis is performed on this and linear displacement plot is obtained.
Case 2: Motion Analysis for 10 mm positive Offset
Motion analysis is performed on this and linear displacement plot is obtained.
Case 3: Motion Analysis for 10 mm Negative Offset
Motion analysis is performed on this and linear displacement plot is obtained.
Superimposed graph: Here the linear displacement graph from each case is exported to excel and then superimposed.
Final Conclusion:
From the plots obtained, we can see that Linear Displacement increases as we move from negative wrist pin offset to positive wrist pin offset i.e. the magnitude of the Linear displacement increases.
Also from the graph obtained after superimposing it, we can see that for a given time-frequency of rotation of piston with wrist pin offset negative is higher compared to one with zero offsets and pin with zero offsets has a higher frequency than one with a positive offset.
Animation:
SolidWorks File Link:
https://drive.google.com/drive/folders/1bFTD6h19rMiBFfbE-gUb7YHkaBFbctLi?usp=sharing