MBD Simulation on IC Engine Valve Train
Aim: To model and simulate IC Engine Valve Train for contact forces among various parts to have a clear Idea of motion and force transmission properly
Introduction: IC engine valve trains are the mechanism which operated the opening and closing of valves while inlet and exhaust strokes of an IC Engine. At the time of inlet it opens the valve to let air fuel mixture enter the cylinder and closes once it fills the cylinder and similar cycle occurs when the exhaust gas is expelled out of the cylinder. There is always a time gap between the inlet and exghaust stroke which is maintained by Cam profile. Various parts of the complete train includes Cam, pushrod, rocker arm, valve and valve stem etc.
The cam is mounted on cam shaft which is attached to the crank shaft of the engine assembly. The rotation of crankshaft transmits the timings of inlet and exhaust stroke. As the cam rotates during compression and power stroke the push rod is slides over the uniform part of the cam and does not push the rocker arm but as soon as the inlet or exhaust stroke starts cam's non uniform part pushes the pushrod in upward direction. As the rocker arm presses the valve downward it gets open for the inlet or exhaust strokes to occur.
Now, the valve is always wrapped with a pre tensioned spring between a sleeve called valve stem and one part of the valve head which helps retain the valve position and closes it.
Animation Link for clear Understanding:
https://drive.google.com/file/d/1GdHa6EVNYrMMbBdS7kNA4bYaXX2vBOD9/view?usp=sharing
Case 1
| Sl.No | CAM Lift (mm) | Speed (RPM) | Material |
| 1 | 3.5 | 1500 | Cast Carbon Steel |
First to achieve cam lift of 3.5 mm we modified our Cam profile
Using Cam lift formulae we have,
Cam lift = (center distance of both circle - radius of lower circle) + Radius of upper circle
Hence,
Cam Lift
`=(12.5-12.5)+3.5=3.5`
Study setup:
Material selection
Input speed of 1500 RPM
We have taken precise contact at 9000 fps with stiffness around 25 N/mm for accurate results
Plotting Various results
Plot 1: Linear Displacement of Valve
In the plot above the as the cam pushes the valve through pushrod and rocker arm, we get the displacement of valve as it opens and pushed back after the stroke.
in the Plot above we can also understand that it remains there for a very short interval of time and halts for a large interval of time after it is back in closed position.
Plot 2: Contact force between Cam and Pushrod
After running simulation upto .2 seconds we have got the plot.
here Contact force if fluctuation fast as the push rod runs over non- uniform part of Cam profile. In the software there is a bit interference of the push rod in the cam profile which can be rectified by using correct stiffness spring and tensioned length.
Plot 3: Contact force between Pushrod and rocker arm
we can see a similar type of fluctuations due to interference.
Plot 4: Comparison of contact forces between Rocker Arm and Valve while measuring with respect to the X direction and measuring with respect to magnitude
Plot 4.1 with respect to magnitude
Plot 4.2 with respect to x direction
The contact force varies at when compared with respect to X axis than the magnitude of the contact force between the rocker arm and valve because in magnitude we see the total effect's direction according to Newton's Second Law but in X-direction only we will see that the rocker arm slides over the valve block which results in the direction of force variation in x-direction
Case 2
| Sl.No | CAM Lift (mm) | Speed (RPM) | Material |
| 2 | 6 | 1500 | Cast Carbon Steel |
First to achieve cam lift of 6 mm we modified our Cam profile
Using Cam lift formulae we have,
Cam lift = (center distance of both circle - radius of lower circle) + Radius of upper circle
Hence,
Cam Lift
`=(12.5-12.5)+6=6`
Plotting Various results
Plot 1: Linear Displacement of Valve
In the plot above the as the cam pushes the valve through pushrod and rocker arm, we get the displacement of valve as it opens and pushed back after the stroke.
in the Plot above we can also understand that it remains there for a very short interval of time and halts for a large interval of time after it is back in closed position. we can also see that due to increase in Cam lift the linear displacement of the valve also increases.
Plot 2: Contact force between Cam and Pushrod
After running simulation upto .2 seconds we have got the plot.
here Contact force if fluctuation fast as the push rod runs over non- uniform part of Cam profile. In the software there is a bit interference of the push rod in the cam profile which can be rectified by using correct stiffness spring and tensioned length. In this case too contact force increases as the cam lift increases
Plot 3: Contact force between Pushrod and rocker arm
we can see a similar type of fluctuations due to interference. In this case too contact force increases as the cam lift increases
Plot 4: Comparison of contact forces between Rocker Arm and Valve while measuring with respect to the X direction and measuring with respect to magnitude
Plot 4.1 with respect to magnitude
Plot 4.2 with respect to x direction
The contact force varies at when compared with respect to X axis than the magnitude of the contact force between the rocker arm and valve because in magnitude we see the total effect's direction according to Newton's Second Law but in X-direction only we will see that the rocker arm slides over the valve block which results in the direction of force variation in x-direction
Link for Cad Files
https://drive.google.com/drive/folders/1QAh44-3W7fsM8ZFsDx49Pjlsi0Q3HBHS?usp=sharing