MBD Simulation on IC Engine Valve Train
REPORT ON MOTION ANALYSIS OF I.C. ENGINE VALVE TRAIN
AIM – To conduct the motion analysis of the I.C. engine valve train, generate and explain the plots for the given conditions.
BODY OF THE CONTECT
- MOTION ANALYSIS
- Assembly of I.C. engine valve train
I.C. engine valve train consists of total five number of components. So first the modeling of all the parts is need to be carried out.
Cam
Cam dimensions are specified by the cam lift formula shown below
Cam lift = (L – R1) + R2
Where
R1 = Radius of lower circle
R2 = Radius of upper circle
L = Center distance between two circle
Cam specifications
|
Radius of lower circle (R1) |
Radius of upper circle (R2) |
Center distance (L) |
|
|
3.5 mm cam lift |
12.5 mm |
5 mm |
11 mm |
|
6 mm cam lift |
12.5 mm |
5 mm |
13.5 mm |
This components gives reciprocating motion from the rotation of it.
Push rod
This component transmits the reciprocating motion to the rocker arm.
Rocker arm
Rocker arm then further transmits the motion to the valve. It act as pivot arm between push rod and valve.
Valve
This is the component up to which the motion from cam is transmitted. It has its end at the inlet of the cylinder. It controls the amount of air entering into the cylinder.
Valve mount
It is the fixed component in the entire assembly. It supports the spring that forces the push rod back to its original position.
Assembly of I.C. Engine valve train
- Motion Analysis
Conditions for motion analysis
|
Sr. No. |
Cam lift (mm) |
Speed (rpm) |
Material |
|
1 |
3.5 |
1500 |
Cast Carbon steel |
|
2 |
6 |
1500 |
Cast Carbon steel |
The rotational speed of the cam is 1500 rpm which means it rotates at the angular velocity of 9000 deg/sec. so in motion analysis the data is generated for each degree of the rotation of the cam hence the value of frame rate is been changed to 9000 frames per second. Also the motion analysis is been carried out with considering the precise contact option.
- RESULTS
- For 3.5 mm can lift
Valve lift
The above plot shows linear displacement of the valve in mm for 3.5 mm cam lift with respect to time. From the lift of approximately around 2.5 mm is observed back and forth. With precise contact and data at each crank angle the plot seems quite uniform which is expected in this application otherwise there will be always variation in the air intake into the cylinder during each rotation of the cam.
Contact force between cam and push rod in magnitude.
The above graph shows the contact force in magnitude between cam and push rod in Newton with respect to time. From the graph it is observed that there is an initial force of around 260 N from the beginning of the cam rotation that is because of the spring force with is in pre tensioned condition before starting the motion. This pre tensioning is very important otherwise there will not be an enough force that will revert back the push rod on the cam after the lift. Further an increase in the force is been seen during the lift through cam which is around 1000 N. As the cam lift gets completed a reduction in the force magnitude is been seen to zero for particular interval of time. After this time interval quickly there in an rise in the force magnitude up to around 3700 N in first cycle of the rotation and around 4700 N in upcoming cycles of the rotation due to the spring force that cause the push rod to again get back to its original position.
Contact force between push rod and rocker arm
The above graph shows the magnitude of contact force between push rod and rocker arm in Newton with respect to time. It is observed that this graph is quite similar to the previous graph of contact force between cam and push rod. Only certain variations in the values of the magnitude of the contact force are observed but the form of the graph is quite same as that of cam and push rod.
Contact force between rocker arm and valve
The above graph shows the magnitude of the contact force between rocker arm and valve in Newton with respect to time. This graph is also seems similar to the previous two graphs except at few intervals of the time also the values of the magnitude of the contact force are different in this case. Here we find that the initial force exerted by the spring due to pre tensioning is small which around 100 N as compare to the previous two cases. The contact force during the time interval of the lift is greater which is around 2000 N than the previous cases. One thing is different in this case than the previous cases is that after the lift is over the contact force does not reach to 0 magnitude it reaches to the value same as the initial value of force of pre tensioned spring and as the dwell period is over and cam starts to decent downwards the spring force is exerted to push the push rod back to its original position around 800 to 1000 N which seems less than the previous two cases.
Contact force between rocker arm and valve in x direction
The above graph shows the contact force in x direction between rocker arm and valve in Newton with respect to time. It is observed that this graph is completely different than all the previous graphs. In this graph the negative forces are also been seen. Here when the direction of the force is downwards then it is taken as positive and when the force acts in opposite direction which is in upward direction then it is considered as negative. So at the initial stage there is a force of – 27 N is seen on the graph which shows that the force act in upward direction with the magnitude of 27 N which is the force exerted by the pre tensioned spring. Then as the lift starts the force of + 50 N is been observed from the graph that shows due to the lift generated by the cam the force at the contact point of the rocker arm and the valve acts in upward direction with magnitude of 50 N. Then as the dwell period over the graph shows the force of around – 190N to – 230 N for first and the upcoming cycles which means the spring force to restore the push rod back to its original position is been acted in the upward direction
Why the graph of contact force between rocker arm and valve in magnitude and x direction are different?
The main reason behind this can be all the previous graphs were magnitude based graph that means the results shown by those graphs were based on the magnitude of the force so there was not any consideration of the direction of the force.
As we know that the force can be represented by two ways which are given in follows
Only by Magnitude
By Magnitude and Direction
When the force is represented only by the magnitude then it represents scalar quantity and when the force is represented by both magnitude and direction then it represents vector quantity.
So all the previous graphs were representing the scalar quantity but now this graph of contact force in x direction represents the vector quantity where the direction of the force is also mentioned in the form of assigning the positive and negative signs to the force magnitude. So that it becomes clear to understand the direction of the force along with magnitude which helps to take right and accurate decision while designing any system.
Hence the graph of contact force between rocker arm and valve in magnitude and x direction are different
- For cam lift of 6 mm
Valve lift
The above graph shows the linear displacement of the valve in mm with respect to time. As per graph the linear displacement of the graph is around 5 mm back and forth. It can be seen that the graph is uniform in nature and that is because of using the precise contact option and also by increasing the frame rate 9000 frames per sec. This helps to get the output data for each degree of the crankshaft rotation. This linear need to be uniform so that it will ensure the equal amount of the air is been entering into the cylinder during each rotation of the crankshaft.
Contact force between cam and push rod
The above graph shows the contact force between cam and push rod in Newton with respect to time for the cam lift of 6 mm. From the graph it can be seen that initially there is the contact force of around 250 N due to the force exerted by the pre tensioned spring. This spring ensure that the push rod is again reach back to its original position after the lift of the cam. When the lift begins the contact force reaches to the value of around 1650 N as per graph. During the swell period of the cam the contact force reaches to zero value. As the dwell period ends and as the cam start to decent the spring force of around 13000 N is exerted at the contact. This force is large as compare to the cam with lift of 3.5 mm that is because with cam of lift 6 mm there is more linear displacement of the valve as compare to the that with 3.5 mm lift. So because of the more linear displacement the amount of the length of the spring getting compressed is more. As the stiffness value of the spring in both the condition is same as 10 N/mm hence due to more linear displacement of the spring in case of the 6 mm cam lift more spring force is generated In this case as compare to the same with 3.5 mm cam lift.
Contact force in between push rod and rocker arm
The above graph shows the contact force between push rod and rocker arm in Newton with respect to time. This graph seems similar to the previous graph in terms of the form of the graph and the values of the forces. That means the behaviour of the contact force between cam , push rod and rocker arm is in a way similar.
Contact force between rocker arm and valve
The above graph shows the contact force between rocker arm and valve in Newton with respect to time. Though the graph looks similar to the previous two graphs but it is not same. There is a difference in the values of the contact force. Here the contact force at initial stage due to the pre tensioning of the spring is around 100 N. which is comparatively less than the previous two cases. Then during the lifting of the cam the force increases to around 280 N. At this contact the contact force during swell period does not reach to zero value. It shows the value around 150 N. after this dwell period the force exerted by the spring is around to 2500 N to 3300 N during the cycles of cam rotation.
Contact force in x direction between rocker arm and valve
The above graph shows the contact force in x direction between rocker arm and valve in Newton with respect to time. As discussed earlier this graph represents the force in vector quantity which means it also consider the direction of the force along with its magnitude. Hence this graph also shows the negative force value. In this graph the forces that act in downward direction are considered as positive forces and the forces that act in upward direction are considered as negative forces. For initial interval of time the graph show value of – 27 N which means the force of magnitude 27 N acts in upward direction at the contact point of the rocker arm and valve. Then as the lift of the cam is starts the value of the force reaches to + 68 N that means at this interval the contact force of 68 N magnitude acts in downward direction due to the lifting of the cam. As the dwell stage starts the force of 49 N acts in upward direction at the contact point. Then as the dwell period ends the upward force of the magnitude 600 N to 800 N is exerted by the spring in order to restore the push rod back to its initial position.
CONCLUSION = From the entire challenge it can be concluded that understanding the plots of the results generated from the motion study is also very important so as to get accurate interpretation of the solutions and take the right decision from those results.