MBD Simulation on a Piston Assembly
MULTIBODY DYNAMIC ANALYSIS OF PISTON ASSEMBLY
1. AIM
To create a piston assembly consisting of five parts such as Piston itself, wrist pin, Connecting Rod, End cap, and Crank which is used in the different mechanical machines such as Internal/External combustion engines, compressors, pumps, radial engines, etc. The main purpose of using this setup is to convert chemical energy (i.e) combustion of fuel into mechanical energy.
2. OBJECTIVE
Our Main Objective is to do motion analysis of Piston kinematics by designing different Parts of the Piston Assembly and assemble them in SolidWorks. Plots are taken using three different conditions as follows.
|
SI. NO. |
WRIST PIN OFFSET |
CRANK SPEED (RPM) |
|
1. |
0 mm |
2000 |
|
2. |
10 mm Positive |
2000 |
|
3. |
10 mm Negative |
2000 |
3. PROCEDURE
Initially, the parts are modeled in Solidworks separately and assembled in an assembly file.
PISTON HEAD
It is the part that reciprocates inside of the engine cylinder through which the chemical energy is burnt and the combustion process pushes the piston in a downward motion. This part is modeled using the above dimension.
WRIST PIN
This part connects the piston head and the connecting rod for transferring the motion to the crankshaft.
CONNECTING ROD
This part helps in transferring the motion from the piston head to the crankshaft.
END CAP
This is a part of the connecting rod which helps in housing the shaft of the crank.
CRANK
The crank converts linear motion into rotational motion and transfers the power to do work in a power-producing device and vice versa in a power-consuming device. Using the above dimensions one side of the crank is modeled and the other side is mirrored.
ASSEMBLY
Assembly is done by importing various parts into the assembly file and are mated to provide a particular motion. The main mate in the process is the coincident mate between the crank and piston axis or both their front planes.
4. SIMULATION & ANALYSIS
We aim to analyze the linear displacement of the piston assembly for various offset values of the wrist pin in the piston head.
NOTE: The center axis of the piston and crank should be coincident.
For all the motion study the rpm and frames per second are a standard value of 2000rpm and 7200fps respectively. All movements are in a clockwise direction.
STUDY-1(0mm offset)
The wrist pin is positioned centrally to the piston head without any offset value.
PLOT
The above plot shows that the linear displacement of piston starts between the 2.0000E+02 and 3.0000E+02. It reaches a maximum of 302mm. The constant curve indicates that the constant linear displacement of the piston to time.
STUDY-2 (10mm offset in the positive direction)
The wrist pin is positioned with an offset value of 10mm in the positive direction from the center of the piston or crank axis.
PLOT
The above plot shows that the linear displacement of piston starts much closer to the 2.0000E+02mm, due to the positive offset provided. The constant curve indicates that the constant linear displacement of the piston to time similar to the previous study-1.
STUDY-3 (10mm offset in the negative direction)
The wrist pin is positioned with an offset value of 10mm in the negative direction from the piston or crank axis.
PLOT
The above plot shows that the maximum linear displacement of piston is closer to the 3.0000E+02mm, due to the negative offset provided. Similar to the previous studies the constant curve indicates the constant linear displacement of the piston to time.
SUPERIMPOSED PLOTS
This plot will depict the variation of plot in terms of time (sec) due to the offset values.
By scaling the time further the variation is observed.
RESULT
Thus from the graph, it is found that the linear displacement of the piston is the same for all the three studies but the time varies, this offset helps the crank reduce the stress that is caused in the rod when it reaches the top or bottom dead center. If there is no offset, then the rod has to bear a lot of loads when moving between TDC and BDC. To avoid this, the wrist pin is offset to value such that the connecting rod forms the arc path.
STUDY-1 (0mm offset )
STUDY-2 (10mm offset in the positive direction)
STUDY-3 (10mm offset in the negative direction)
SOLIDWORKS PART FILES
https://drive.google.com/drive/folders/1UKpjwdzLiySSjlQ1BvrSaWE5IWlUJirG?usp=sharing