MBD Simulation on a Piston Assembly - SolidWorks

MBD Simulation on a Piston Assembly - SolidWorks

1. AIM:

To model and carry out motion analysis on a piston assembly.

2. INTRODUCTION:

- A piston 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.

- The piston head is the top surface (closest to the cylinder head) of the piston which is subjected to tremendous forces and heat during normal engine operation.

- A piston pin (Gudgeon pin) is a hollow shaft that connects the small end of the connecting rod to the piston.

- A connecting rod, also called a con rod, is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the crankshaft.

- A crankshaft is a rotating shaft which (in conjunction with the connecting rods) converts reciprocating motion of the pistons into rotational motion.

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

3. OBJECTIVES:

- To carry out motion analysis on piston assembly.

- To test 3 cases of the piston assembly as given below and plot linear displacement of piston head and superimpose them on a single graph.

Sr.No.	Wrist Pin Offset	Crank Speed (Rpm)
1	"0" mm	2000
2	10 mm Positive	2000
3	10 mm Negative	2000

4. FLOW OF PROJECT:

1. Create 3D CAD models.
2. Assemble the CAD models using proper constraints.
3. Use the assembly in motion analysis and set-up the motion parameters like rpm, material, contacts etc.
4. Run the calculations.
5. Save animation and plot the required graph.
6. Switch to other cases and repeat calculations.
7. Save the animations.
8. Plot graphs.

5. MOTION STUDY SETUP:

1. Initially, the 3D CAD models for different parts of the piston assembly are created in Solidworks.
2. Assembly with proper constraints is then done and basic motion is checked using drag mouse technique.
3. A new motion study having type as Motion Analysis was selected.
4. In analysis settings, precise contact is turned ON and frames per second is set to 12000 as 2000RPM translates into 12000 deg/sec and we need to capture every single degree in our calculations.
5. Contacts between every touching component is defined with material as steel(dry).
6. The crank is set to the RPM as defined in first case and then subsequent cases.
7. Gravity is turned on in the downward direction.

6. OBSERVATION, RESULT AND CONCLUSION:

Actual 2000RPM animation:

Case 1: 0mm Wrist pin offset @2000RPM

- After exporting the values and plotting the graph in MS Excel, the maximum and minimum values of Linear Displacement were found out to be 302.500mm and 202.500mm respectively.

Case 2: Positive 10mm wrist pin offset (clockwise) @ 2000RPM

- After exporting the values and plotting the graph in MS Excel, the maximum and minimum values of Linear Displacement were found out to be 302.307mm and 202.192mm respectively. These values are lower than the values of piston assembly without offset.

Case 3: Case 2: Negative 10mm wrist pin offset (clockwise) @ 2000RPM

- After exporting the values and plotting the graph in MS Excel, the maximum and minimum values of Linear Displacement were found out to be 302.309mm and 202.192mm respectively. These values are lower than the values of piston assembly without offset. These values also almost are equal to the case where there is positive 10mm offset of the wrist pin.

Superimposing all 3 graphs on 1 graph:

- We can clearly see that the minimum and maximum values we had got from graph of Linear Displacement of Piston head, the Blue color graph stands out because of its higher maximum displacement and minimum displacement.

- The difference exists in case 1 and cases 2,3 because the connecting rod is not perfectly vertical thus its full length does not contribute in giving maximum linear displacement.

- Case 2 and Case 3 had same values approximately so those 2 graphs are perfectly on top of one another.

Why the blue (Case 1) graph is moving forward than the rest 2 graphs?

- It is because the Linear displacement of piston head in case 2 and case 3 is lower, thus their cycle is faster than the case 1 where there is no offset. Thus Case 1 needs a bit longer to complete the cycle hence the graph seems like it is moving ahead of the graph of case 2 and case 3.

- Also, since the cycle speed is faster in case 2 and case 3, This offset is beneficial for race cars and racing engines.