MBD Simulation on IC Engine Valve Train
Aim: To simulate the Multi-Body Dynamics of IC Engine Valve Train Assembly.
Theory: The valve train in the IC engine is responsible for opening and closing of inlet and outlet valves at appropriate times. The cam-shaft is coupled with the crank-shaft using valve timing gear, which helps in setting the timings for the operation of respective valves.
The Valvetrain assembly is based on the cam and follower mechanism. The follower here is the pushrod which in turn actuates the rocker arm connected to the valve. The return (or closing) of the valve is ensured with a spring. This spring gets compressed when pushrod travels upwards due to cam movement and gets expanded late on giving the return motion.
It consists of five components:
- Cam
- Pushrod
- Rocker Arm
- Valve
- Spring
Geometry Modelling: Two Cams are designed for the respective cases with the following dimensions.
Cam Lift1 = `(11 - 25/2) + 10/2` = 3.5mm
Cam Lift2 = `(13.5 - 25/2) + 10/2` = 6mm
The other parts are designed as per given instructions and dimensions. The cam is constrained for all translation motions and is allowed to rotate only along its axis. The pushrod is rested over the cam’s side face which will act as the follower (for cam-follower mechanism). The pushrod is constrained to translate in the vertical direction only allowing it to transfer its motion to the rocker arm which in turn acts as a lever actuating the puppet valve.
Motion Study Setup: The material used is Steel (Dry) which provides a static friction coefficient of 0.3 and a kinematic friction coefficient of 0.25.
A motor is attached to the cam to induce motion. Further contacts are made connecting all solid bodies.
Contacts:
- Cam and Pushrod
- Pushrod and Rocker Arm
- Rocker arm and valve
Setup Settings:
|
Precise Contact |
ON |
|
Motor RPM |
1500 |
|
Frames per second |
7200 |
Results: The graphs obtained for both the simulations are smooth indicating proper functioning of the mechanism.
Graphs:
Cam Lift: 3.5mm
Cam Lift: 6mm
Conclusion:
The contact force increases with an increase in cam lift at all the contacts.
The contact force between Rocker Arm & Valve differs when measured along x with respect to when measured magnitude because the force along x is purely frictional and it changes from positive to negative as the rocker arm starts turning back towards the cam. Whereas magnitude is root-over-squared-sum of forces along all the three directions. Hence it is always positive.