MBD Simulation on a Piston Assembly

AIM – Motion Study of Piston Assembly Gear Set using Solidworks Motion

Objectives – Our objective here is to do Motion Study of Piston Assembly and Obtain the Linear displacement of the Piston Head. Calculate the required values for the Planet gear.

1 Modelling –

As per the given video, we have created solid MODLES of all the Parts viz. Piston Head, Gujan/Wrist Pin, Connecting Rod, End Cap, Crank. Now we have to variate the Piston Head as given below and perform the motion study for each and every case.

Sr. No.	Wrist Pin Offset (mm)	Crank Speed (Rpm)
Case 1	"0" mm	2000
Case 2	10 mm +ve	2000
Case 3	10 mm -ve	2000

Table – 1.1

Crank

Connecting Rod

End Cap

Wrist Pin

Piston Head

• Changes for Case 1 –

We have just need to change the hole we created (which is shown below), but per Case 1 we do not need to change the hole.

For Case 1 we have a Piston Head (0 mm offset) which is shown –

Fig – 1.1

2 Assembly –

In order to perform Motion Study, we have created Assembly consisting of all part mentioned above.

2.1 Assembling the Parts Together –

Basically, we need –

• Crank to only have 1 rotational DOF (Degree of Freedom)
• Attach End Cap and Connecting Rod together
• Connect Connecting Rod to Crank having sliding and rotating DOF
• Piston head to slide
• Wrist Pin to rotate and slide with respect to Connecting Rod

In order to do that we have to fix the DOF (Degrees of Freedom) which are not needed, there are in total 6 Types of Degrees of Freedom –

• 3 Translation Motion (Along X, Y and Z-Axis)
• 3 Rotary Motion (Along X, Y and Z-Axis)

Follow the steps below –

Step – 1 (Crank)

Fig 2.1

Distance from Front Plane to make it in Centre

Fig 2.2

Step - 2 (Connecting Rod and Crank)

Fixing Axis on Top and Right plane to just have Rotational DOF

Fig 2.3

Connecting the End Cap with the body

Fig 2.4

Connecting Crank with Connecting Rod with an offset of 1mm and coinciding the axis with the cranks' axis.

Step - 3 (Wrist Pin with Piston)

Fig 2.5

Coinciding the axis of both

Step - 4 (Making Connecting Rod Piston and Wrist Pin Coincident)

Fig 2.6

Using 3 Mates here

1. Making the Wrist pin and Connecting Rod axis coincide with each other.

2. Making Wrist pin in the middle of Piston by coinciding Front Plane of both (Dotted Orange and Blue)

3. Making Piston and Wrist pin in the middle by doing the same (Blue and Orange)

Step - 5 (Allowing Piston to only have Sliding Motion (Up and Down))

Fig 2.7

Making Assembly Right Plane and Pistons' Right plane coincide with each other.

3 Motion Study –

Now in order to perform the Motion Study, we need Solidworks Motion “ENABLED”.

We need to perform motion study for the Linear Displacement of Piston Head having different locations o wrist pin. For that we are having the table

Sr. No.	Wrist Pin Offset (mm)	Crank Speed (Rpm)
Case -1	"0" mm	2000
Case -2	10 mm +ve	2000
Case -3	10 mm -ve	2000

Table – 3.1

Now on the basis of the table as we have shown above we have no offset now, to do the motion study, we have shown motion study for Case -1.

Case – 1

Wrist Pin – 0 mm offset

Follow the steps explained from the next page.

Fig – 3.1

Step 1 – We need to select Motion Study and Motion Analysis as shown in Fig – 3.1 and then tap on the icon which is shown in the figure. (Solidworks motion and Select Motion Analysis)

Fig – 3.2

Step 2 – We need to apply a Motor to Crank entering value of 2000 RPM as shown in Fig – 3.2.

Step 3 – In order to run the Motion Study successfully, we need to apply contacts as shown below.

Fig – 3.3

Step 4 – We need to select all the bodies which comes in contact with each other through which the power is being transmitted. Observe Fig – 3.3 we can either select individual part or just click and drag out the mouse icon selecting whole part, this will allow us to give all the contacts in a single run.

Step 5 – After giving contacts we need to set Frames per Second, this basically means how many frames Solidworks will capture as a DATA or VALUE per second, e.g. if we have selected 10 RPM so that means Motor will rotate 360° for 10 times so that makes 3600° so in order to catch every degree we will need 60 frames per second (1 rpm = 0.0166 fps), so now if we have 2000 RPM the fps requirements will go very high which will result in heavy calculation, load on CPU and will require significantly more time to calculate. So here we have selected 7200 fps, which will make the Motion Study smoother and more fluent when in working condition. As shown in Fig 3.5

Fig – 3.5

Step – 6 Now we will plot the graphs for the output by selecting the Results > Displacement > Linear Displacement > Magnitude, and then select the Piston Head. Follow as shown in Fig – 3.6.

Fig – 3.6

4 Conclusion –

For given tasks, we have performed the following –

• Linear Displacement of Piston Head

4.1 Results for Case 1 –

Fig 4.1

Above plot for 0 mm offset forms a smooth sinusoidal wave and the plot is uniform, this is due to the linear movement of the Piston head (up and down), from the graph it can be observed that it is 100 mm from its initial position w.r.t the geometry.

Now we need to change the offset as given in Challenges, images of which is shown below.

Fig 4.2

Fig 4.3

Following the same steps as shown above for Motion study we have the following results, (10 mm +ve followed by 10 mm -ve offset)

4.2 Results for Case – 2

Fig 4.4

4.2 Results for Case – 3

Fig 4.5

Superimposing all the three Plots and Observation

Fig 4.6

Blue – 0 mm

Orange – 10 mm +ve

Grey – 10 mm -ve

As we can see from the above superimposed plots, 0mm offset and 10 mm -ve (Blue and Grey) offset both are superimposed quite well and its higher and lower values are same which is clearly the amount of distance travelled by the Piston but it is going out of sync which is clearly visible because of the distance between those two, reason of which is because of the varying time at which Piston head reached either (up or down / high or low) position. Now if we consider 10 mm +ve offset we can see that it is not as Synced with another tow. Which is again can be explained on the basis of the value amount of time which it took to reach the initial or final position.

Other observation that we can get from these superimposed graphs if that the most efficient time in which Piston can travel Up and Down is 0 mm, as each stroke has less time as compared to other two.

Link for Above Model Assembly and Animation is given below -

https://drive.google.com/drive/folders/1D484-VVIEQKB3CiDwjgEv6WyZjet9XIu?usp=sharing