MBD Simulation on IC Engine Valve Train
Aim: To perform motion analysis on IC Engine Valve Train
Objective:
The main objective to model different parts of IC Engine Valve Train, assemble them and perform motion analysis for following cases:
| Sr. No. | Cam Lift (mm) | Speed (RPM) | Material |
| 1 | 3.5 | 1500 | Cast Carbon Steel |
| 2 | 6 | 1500 | Cast Carbon Steel |
Theory:
During operation of IC engine, in each cycle, the inlet and exhaust valve is turned on and off and to automate this motion valve train is used. It consists of cam, pushrod, rocker arm, valve and valve mount.
Cam and Rocker arm has a rotary motion and pushrod and valve has tanslation motion while valve mount is pratically fixed and provide support to the valve.
Cam lift is given by the formulae,
Cam lift = L - R1 + R2
where,
R1 = Radius of lower circle of cam
R2 = Radius of upper circle of cam
L = Center distance betweem two circles
For this study,
R1 = 12.5mm
R2 = 5mm
For Cam lift = 3.5mm
L = 3.5 + 12.5 - 5 = 11mm
For Cam lift = 6mm
L = 6 + 12.5 - 5 = 13.5mm
Parts are modelled and assembled in solidworks and the assembly is shown below:
After applying constraints, to setup assembly for initial position the valve is moved with move component command with physics dynamics option turned on. Physics dynamics allows to move the parts without applying any contacts.
Motion Analysis:
To perform motion analysis cam is provided with a rotary motion of 1500RPM and contacts are defined between all the mating parts.
To apply material, box select all the parts and then right click and choose material and then click on edit material. Cast carbon steel is applied to all the parts in this study.
A spring is applied between valve and valve mount to push back valve to its original position. The spring with stiffness of 10N/mm is used with a pre-tension of 10mm.
To caputer all the frames during motion, frame rate of 9000FPS is choosen and precise contact is choosen for accurate results.
The results for both the cases are shown below:
Case 1 : Cam Lift - 3.5mm
Case 2 : Cam Lift - 6mm
Conclusion:
From valve lift results for both the cases it can be concluded that with increase in cam lift, valve lift increase and that is what expected. Also it can be noted that with increase in cam lift, contact forces between parts increases significantly.
It can also be noted that contact force between cam and pushrod and between pushrod and rocker arm are almost same but it is quite less between rocker arm and valve and it is because part of the force applied by rocker arm on valve is absorbed by the spring.
Note: There is difference in contact force between rocker arm and valve when measured with respect to magnitude and when measured with respect to X direction. This is because during assembly valve mount was not fully constrained, it was free to rotate with respect to y axis about its part origin. Due to this during motion analysis valve gets little displacement in X direction and as a result contact force reduces in that direcction. This problem can be fixed by making valve mount right plane parallel to assembly plane.