MBD Simulation on IC Engine Valve Train

Aim: To perform the MBD simulation on IC Engine valve train.

Introduction: This study is about the motion or behavioural study of a valve train mechanish. In this setup we provide a rotaional motion to the cam and as the mates are provided to the parts they transmits the motion of the cam to the push rod further to the rocker ran and than to the valve. This leads to the opening of the valve to complete the cycle of an IC Engine.

The Motion Study helps us to see the motion of the valve train parts with respect to each other. Using the motion study we can analyse the displacement of different parts and can trace the motion and the travel path of a particular component. We can also derive the various force between the two components and the bevaviour of the components due to such forces. Using these datas an engineer can look furter to make the the parts in a more efficient and economical way.

Setup of Motion Study:

1. Firstly we will model the parts.
2. Then we will assembly them all in the assembly and provide them with proper mates.
3. We willl further keep the parts in position such that there is minimal gap seen between the parts.
4. Further using the move components section and from there we will go to physical dynamics. Using physical dynamics we can just move a particular component and that will move all the components removing all the gaps between the components forming a contact between each other.
5. Further by activating the motion study from the solidworks add-in optuon we can move to motion study.
6. Then we provide the motor to the cam with a revolution of 1500 RPM.
7. Than we will provide the conatacts between the components.
8. Also we need to take care that we provide a proper material which has all the datas to perform the calculations. In our case we will take material as cast carbon steel.
9. Then we will provide the spring between the valve and the valve steam with a spring constant of 10 N/mm and a pre-compression of 10 mm.
10. Then by providing the time frame for the simulation to run, we can hit the calculate button to run the calculation.
11. Once the calculation is completed we can go on to the plot result section and derive various results for motion and displacement as required.
12. We will repeat this process twice for the two cases of cam displacement.
13. Also we can export the ploted result in the excel sheetto have a detailed report.

The cad models of each parts can be seen as:

To calculate the cam lift we can use the formula as below

For our calculations we will take the centeral or base circle as ⌀25 mm and the small circle as ⌀10 mm.

Using the formula for the first case i.e. for 3.5 mm lift, we come to know that the centre distance between the circle as 11 mm.

Here I am just uploading the Screen shots of the parts.

Cam for 3.5 mm lift:

Push Rod:

Rocker Arm:

Valve:

Valve Stem:

Assembly:

Assembly in Isometric view:

For Case 1: that is 3.5 mm cam lift

The animated video of the motion study for the cam lift of 3.5mm can be seen below:

Note that the animation is shown at 10sec.

Graph No 1: Valve Lift

From the above graph we can see that in our setup, for the cam lift of 3.5 mm we are getting a valve displacement of about 2.5 mm. It also indicates that our setup takes 10 cycles within 0.30 seconds.

Graph 2: Contact Force between Cam and Push Rod

The graph represents the contact force between the cam rod and the push rod, if we run the animation while the plot is visible we can see that the highest force is experienced when the maximum lift is acheived. The force is mainly created by the reaction force generated by the reaction force of spring compression.

Graph 3: Contact Force between Push Rod and the Rocker Arm

Here also the contact force is maximum at the maximum cam lift that is when the nose of the cam touches at the push rod.

Graph 4: Contact Force between Rocker arm and valve(Magnitude)

Graph 5: Contact Force between Rocker arm and valve (X direction)

The contact force between the Rocker Arm and the valve in magnitude represents the resultant of the forces in all X, Y and Z direction. Whereas the contact force in X direction represents the forces generated in X direction itself.

The force vector in X direction is more when the cam is moving in the upward direction thus the graph is ploted in the upward direction whereas the friction force is less when the cam is traveling in the downward direction, hence the graph is plotted in the negative direction.

For Case 2: that is 6 mm cam lift

Now keeping the base circle as ⌀25 mm and small circle as ⌀10 mm we will use the formula again to calculate the distance between the two to get the cam lift of 6 mm.

Using the cam lift formula agian we get the value for centre distance as 13.5 mm.

The screen shot of the same cam model can be seen below:

The animated video of the motion study for the cam lift of 6 mm can be seen below:

Note that the animation is shown at 10sec.

Graph No 1: Valve Lift

With the increase in the cam lift of 2.5 mm the valve open is also extended by 2.9 mm for the same RPM of 1500.

Graph 2: Contact Force between Cam and Push Rod

Graph 3: Contact Force between Push Rod and the Rocker Arm

Graph 4: Contact Force between Rocker arm and valve(Magnitude)

Graph 5: Contact Force between Rocker arm and valve (X direction)

The behaviour of the graphs with 6 mm cam lift are same as the one acheived in the cam of 3.5 mm lift.

In all the graphs the values are more in the 6 mm of cam lift compaired to the one at 3.5 mm lift.

This is because as the cam rotates providing more lift to push rod more spring reaction is generated which leads to more contact force generation between the parts.