MBD Simulation on a Piston Assembly

MOTION ANALYSIS OF PISTON ASSEMBLY

Aim:

• To create CAD model of all the parts of piston assembly and assemble all the parts.
• To do the analysis using 3 different conditions.

Wrist pin offset: The position of the wrist pin is going to be varied as shown in below images:

CASE 1: No Offset

CASE 2: 10 mm positive offset-If the crank rotation is in clockwise direction

CASE 3: 10 mm Negative offset- If the crank rotation is in clockwise direction

PROBLEM STATEMENT:

Obtain the linear displacement of the Piston Head in all the above 3 cases. Then export the graphs to excel and then superimpose all the 3 graphs into a single graph.

CAD model of parts of Piston Assembly in SolidWorks Software:

• Piston-Head
• Crank
• Gudgeon pin/ Wrist pin
• Connecting rod
• End cap

Piston-head:

• A piston is a moving head enclosed in a cylinder which is made gas tight by rings. The head moves inside the cylinder as liquid/gas inside the cylinder expands and contracts.
• A piston is used in transformation of heat energy into mechanical work or mechanical work to heat energy.
• Below figure shows an example of a piston cycle, in which heat is converted to mechanical work.
• 

Crank:

A crank is an arm attached to the right angle to a rotating shaft by which circular motion is imparted to or received from the shaft.

When it is combined with the connecting rod, it can be used to convert the circular motion into reciprocating motion or vice versa.

Wrist-Pin / Gudgeon-Pin

The engine piston is connected to the connecting rod with the help of a hollow hardened steel tube called as Wrist pin or Gudgeon pin.

Connecting Rod:

A connecting rod is a connection between the piston and a crankshaft. The connecting rod carries the power thrust from piston to the crankpin and hence it must be very strong and rigid. Also it should be light as possible.

Endcap:

Steps for motion analysis:

Note: In positive and negative offset cases the crank rotation is in Clockwise direction.

• Activate motion analysis and select the motion analysis check mark from the left side.
• The motor is given to the crank and it is set to 2000 rpm
• After that apply the contacts from the “Contacts” option from motion analysis option
• The calculation of FPS is as follows:
• 2000RPM = 33.34 FPS
• Therefore, to get each degree as a frame we need to multiply 360 with FPS,
• So, 33.34 x 360 = 12000 FPS
• Gravity in y-direction has been added of 9806.65mm/s^2.
• After all the setup has been done “CALCULATE” option is selected and the results and plots are obtained as follows:

Solid Bodies contacts are shown as below:

The first contact set is applied between the crank and end cap:

NOTE: BLUE color indicates the contact sets.

The second contact set is applied between the crank and connecting rod:

NOTE: BLUE color indicates the contact sets.

The third contact set is applied between connecting rod and the wrist-pin:

NOTE: BLUE color indicates the contact sets.

The fourth contact set is applied between the wrist pin and the piston head:

NOTE: BLUE color indicates the contact sets.

Gravity is applied as shown below:

Motion analysis settings:

Results and Observations of 3 different cases:

A

Result of Case 1: No Offset

• The linear displacement vs time graph is sinusoidal curve.
• Maximum value achieved is = 47 mm
• Minimum value achieved is = 44 mm

Result of Case 2: Positive Offset

• The linear displacement vs time graph is sinusoidal curve.
• Maximum value achieved is = 47 mm
• Minimum value achieved is = 44 mm

Case 3: Negative offset

• The linear displacement vs time graph is sinusoidal curve.
• Maximum value achieved is = 50 mm
• Minimum value achieved is = 50 mm
• 

Comparison of the results:

Conclusion:

From the above table we can see that values of No offset and positive offset are almost same while that of negative offset is slightly more.

ANIMATION LINKS:

https://youtu.be/IDj27-pOG2c

https://youtu.be/d3cucariMU0

https://youtu.be/nbNaxGfAEG8

References:

https://energyeducation.ca/encyclopedia/Piston

https://www.theengineerspost.com/connecting-rod/

https://en.wikipedia.org/wiki/Crank_(mechanism)/