MBD Simulation on a Piston Assembly

AIM: To evaluate the linear displacement of Piston head in different cases.

Objectives:

• To have a motion analysis when the pin of the piston have some offset distance from the Crank axis.
• Also, to compare the different analysis when there is no offset distance.

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.

In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder.

In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder.

Modelling of the Parts:

The Reciprocating piston for this project includes the piston, piston-pin, connecting rod, cap ends of connecting rod and crank.

The Reciprocating Piston mechanism also includes other components such as crank case, etc but currently we are not including this as a part of the project.

The parts of the reciprocating piston are modelled as per the dimensions specified by the skill-lync.

Piston:

Piston Pin:

Connecting Rod with Cap Ends:

Crank:

Motion Analysis:

Case(1):

When the crank is rotating in clockwise direction & the piston pin have NO offset.

Here, we have to make the assembly as described in the video section only.

No any further changes have to be done so i am not describing the details & directly jumping to the motion analysis part.

Now after assembling all the components it will look something like this:

After Assembling the components we will go through the motion analysis :

• For Motion analysis we would have to make contacts between the surafces step by step.
• We will provide contact between piston & piston pin.
• Then we will provide contact between piston pin & connecting rod.
• Then we will provide contact between connecting rod & crank.
• Then we will provide contact between cap end & crank.
• Then we will provide a motor at the crank axis.
• The motor speed will be equal to 2000 RPM.

Now we will plot the linear displacement of the piston face;

Result:

The piston travels the linear displacement as shown in the above plot.

The distance that piston can travel is equal to 313 mm starting from 215 mm.

From this graph we can know the position of the piston head at any interval of time.

Similarly we can obtain the degree turned by the crank during the time interval.

Case(2):

When the crank is rotating in clockwise direction & the piston pin have positive offset.

• To have a piston pin a positive offset considering that the the crank is rotating in a clockwise direction.
• We have to make a circle in the front plane of the piston whose centre is 40 mm below the centre of the plane and 10 mm to the left of the axis of the piston as shown in above figure.
• Then we have to extrude cut it through all the surfaces.
• After that we have provide a seat for the piston pin so that it can rest over it.
• I have followed the same procedure for making a seat as described in the video.
• Now, we will go for the assembly.
• The assembly is follows the same procedure as described in the video.

Now after assembling all the components it will look something like this:

After Assembling the components we will go through the motion analysis :

• For Motion analysis we would have to make contacts between the surafces step by step.
• We will provide contact between piston & piston pin.
• Then we will provide contact between piston pin & connecting rod.
• Then we will provide contact between connecting rod & crank.
• Then we will provide contact between cap end & crank.
• Then we will provide a motor at the crank axis.
• The motor speed will be equal to 2000 RPM.

Now we will plot the linear displacement of the piston face;

Result:

The piston travels the linear displacement as shown in the above plot.

The distance that piston can travel is equal to 313 mm starting from 215 mm.

From this graph we can know the position of the piston head at any interval of time.

Similarly we can obtain the degree turned by the crank during the time interval.

Case(3):

When the crank is rotating in clockwise direction & the piston pin have negative offset.

• To have a piston pin a negative offset considering that the the crank is rotating in a clockwise direction.
• We have to make a circle in the front plane of the piston whose centre is 40 mm below the centre of the plane and 10 mm to the right of the axis of the piston as shown in above figure.
• Then we have to extrude cut it through all the surfaces.
• After that we have provide a seat for the piston pin so that it can rest over it.
• I have followed the same procedure for making a seat as described in the video.
• Now, we will go for the assembly.
• The assembly is follows the same procedure as described in the video.

Now after assembling all the components it will look something like this:

After Assembling the components we will go through the motion analysis :

• For Motion analysis we would have to make contacts between the surafces step by step.
• We will provide contact between piston & piston pin.
• Then we will provide contact between piston pin & connecting rod.
• Then we will provide contact between connecting rod & crank.
• Then we will provide contact between cap end & crank.
• Then we will provide a motor at the crank axis.
• The motor speed will be equal to 2000 RPM.

Now we will plot the linear displacement of the piston face;

Result:

The piston travels the linear displacement as shown in the above plot.

The distance that piston can travel is equal to 313 mm starting from 215 mm.

From this graph we can know the position of the piston head at any interval of time.

Similarly we can obtain the degree turned by the crank during the time interval.

SuperImposing all the plots in the single plot:

Though all the plots look alike, we barely notice a change in the plots, so to get the effcet of the offest given at the piston pin, we have to super impose all the above plots into single plot.

The below plot have been made using microsoft excel.

The Below plot has three curves of three different colour namely, orange, blue and red.

The blue coloured plot shows the piston with No offset.

The orange coloured plot shows the piston with positive offset.

The yellow coloured plot shows the piston with negative offset.

Conclusion:

From the above plot it is found that the piston with negative offset covers more distance in less time at starting & then the positive offset & then the piston with no offset.

After 2-3 revolution or at time just before 0.1, the piston head with positive & No offset meet at point & then they have moving & covering the position with some minimal gap. While the piston head with negative offset is been late by 1 revolution at that time.