MBD Simulation on a Piston Assembly

Aim :- To model all the parts of the piston assembly and then to assemble them in SolidWorks & to obtain motion analysis of it

Objective :-

• To model all the parts and then assemble them in SolidWorks
• To run the motion analysis for three different conditions, 0 mm wrist pin Offset ,10 mm Positive Offset & 10 mm Negative Offset . for the crank speed of 2000 rpm for all

Theory :-

Piston- Crank Mechanism is a demonstration of a simple mechanical system of linkages and motion chains. The objective is to display the working of a piston inside an engine cylinder and how the reciprocating motion of the piston gets converted to rotational motion of the crank.

When the piston is manually pushed and pulled in vertical direction, the connecting rod which connects the piston to the crank transmits the power to the crank wheel which rotates about its crank-shaft axis.

The power/torque of the crank shaft rotation is transmitted to the wheels which drives the vehicle.

Parts / 3d Models :-

1.Piston:-

2.Connecting Rod :-

3.End Cap :-

4.Wrist Pin :-

5.Crank :-

Assembly :-

• FOR CASE 1 :- 0 mm wrist pin Offset

- The below snap shows the centre axis of the crank and the piston aswell as the axis of the wrist pin all three are coincident to each other

- That means there is 0mm wrist pin offset from the axis of the piston head

- The assembly for the following condition is also shown below with the motion study

- The motion analysis for this condition was ran for 0.23 sec for rotar speed of 2000rpm at 7200fps and the smooth curve plot for the linear displacement is obtained

• FOR CASE 2 :- 10 mm positive wrist pin Offset

- The below snap shows the centre axis of the crank and the piston head are coincident to each other

- The axis of the wristpin is shifted to the left at 10mm from the centre axis of the piston head

- That means there is 10mm positive wrist pin offset from the axis of the piston head , thus the wrist pin axis lies on the same plane as of the other two but axis of it is not coinciding with the crank axis

- The assembly for the following condition is also shown below with the motion study

- The motion analysis for this condition was ran for 0.5 sec for rotar speed of 2000rpm at 7200fps and the smooth curve plot for the linear displacement is obtained

• FOR CASE 3 :- 10 mm Negative wrist pin Offset

- The below snap shows the centre axis of the crank and the piston head are coincident to each other

- The axis of the wristpin is shifted to the right at 10mm from the centre axis of the piston head

- That means there is 10mm negative wrist pin offset from the axis of the piston head , thus the wrist pin axis lies on the same plane as of the other two but axis of it is not coinciding with the crank axis

- The assembly for the following condition is also shown below with the motion study

- The motion analysis for this condition was ran for 0.5 sec for rotar speed of 2000rpm at 7200fps and the smooth curve plot for the linear displacement is obtained

Explanation :-

• Software used solidworks-2016
• To draw the 3D part, we start from the selecting the part design providing the proper dimension and using proper drawing tools to create the 3d model of the parts for the piston assembly
• Now we have the dimensions or the details provided in the video using the same we can obtain the different 3d parts like piston, connecting rod, crank, wrist pin etc.
• Using the command Extrude boss base to convert the 2D drawing to 3D
• The fallowing parts are shown in the above snap used for the piston assembly.
• The next step is to assemble the all parts to obtain a motion between them
• Now to start with the assembly drawing, selecting the parts created for the piston assembly and to assemble it using the mating/Mate command
• Inserting one by one part to the assembly drawing, assembly is the process where all the desired generated parts like piston, crank, connecting rod, wrist pin, etc. are assembled to obtain the desire model
• Using the co-incident mate command, the whole setup is properly mated to the desired plane and to the desired axis.

• Now as the part of the challenge for the three different conditions, the motion analysis is going to be carried out as 0 mm wrist pin Offset ,10 mm Positive Offset & 10 mm Negative Offset. for the crank speed of 2000 rpm for all

• FOR CASE 1 :- 0 mm wrist pin Offset

Here the wrist pin and piston have the same axis & in the assembly the center of the axis of the piston head and the crank are coincident to each other

• FOR CASE 2 :- 10 mm Positive Offset

Here the piston is so created that the wrist pin axis is 10mm offset to the left from the axis of piston & in the assembly the center of the axis of the piston head and the crank are coincident to each other

• FOR CASE 3 :- 10 mm Negative Offset :-

Here the piston is so created that the wrist pin axis is 10mm offset to the right from the axis of piston & in the assembly the center of the axis of the piston head and the crank are coincident to each other

• Now it’s time for the motion study, as asked in the challenge using the motor to rotate the crank with 2000rpm, for all the three cases.
• Providing the timeline for the motion study and calculate the motion study. For say 5-10 seconds thus this will create motion analysis of the Piston mechanism and desired simulation/animation of the motion is created
• Lastly using the plot/figure function to obtain graphs for the linear displacement w.r.p to time of the piston head for all the three cases.

Result / Conclusion :-

• Thus we have studied the MBD Simulation on a Piston Assembly
• Also modelled all the necessary parts like piston,connecting rod,end cap,wrist pin, crank and assembled them for the piston assembly
• Ran the motion analysis study for the three diffrent conditions given in the challange
• Obtained the plots for the linear displcement of the piston head for the three diffrent cases.

• The drive link for the parts and assembly is given below:-

https://drive.google.com/drive/folders/1ahKDWzwKaQewxWgXg54yDVXCu0K2r3xL?usp=sharing

• The link for the Video on the motion of the piston assembly is given below:-

Motion Analysis Video :-

FOR CASE 1 :- 0 mm wrist pin Offset :- https://youtu.be/MBRWofMhJ8M

FOR CASE 2 :- 10 mm Positive Offset :- https://youtu.be/FuGz8JiAWfI

FOR CASE 3 :- 10 mm Negative Offset :- https://youtu.be/8-Sf9nzTtJo

Note :- Run the video for 0.25x playback speed to view the smooth motion of the piston assembly.

• The graphs/plots obtained are shown below :-

Graphs / Plots :-

FOR CASE 1 :- 0 mm wrist pin Offset :-

A plot of linear displacement with time of piston head for 0mm offset

FOR CASE 2 :- 10 mm Positive Offset :-

A plot of linear displacement with time of piston head for +10mm offset

FOR CASE 3 :- 10 mm Negative Offset :-

A plot of linear displacement with time of piston head for -10mm offset

Superimposing of the three graphs :-

- The 3 graphs are superimposed and the following observations are made

• The displacement of zero offset case is seems to be slightly more than that of +10 mm offset & -10mm offset
• The +10 mm offset case looks to be lagging behind the 0 mm offset case for the same displacement.
• The smooth flow is seen in the graph for all the three cases.