MBD Simulation on IC Engine Valve Train
AIM:
To model parts, make assembly and create a motion study and motion analysis on the IC engine valve train and study its its motion by creating plots about the following contact forces with rrspect to time:
The contact force between
- Cam and Push Rod
- Pushrod and Rocker Arm
- Rocker Arm and Valve
INTRODUCTION:
IN this simulation, we have to model the given parts, assemble them and then perform motion analysis on them according to the following conditions:
| Sl.No | CAM Lift (mm) | Speed (RPM) | Material |
| 1 | 3.5 | 1500 | Cast Carbon Steel |
| 2 | 6 | 1500 |
Cast Carbon Steel |
The motion is carried out by placing a 1500 RPM motor on the axis of the cam and then applying solid contact between the necessary parts. These were carried out along with placing a spring between the faces of the valve and valve root. And after the simulation is carried out, necessary plots were derived.
The cam lift is given by:
THEORY:
The valve train assembly is responsible for the opening and closing of the valve openings of the engine during its combustion cycle. The defaultpostion of the valve remains as closed because of the spirng between the valve and the valve root. But when the rocker arm pushes the valve, the spring compresses and the valve opens. The reapeated motion of the rocker arm is carried out by the combined motion of the cam and the pin. The cam rotates and transmits its rotaional motion to linear motion to the pin which in turn pushes the rocker arm and hence, the opening and closing of the valve is simulated. This entire motiob helps toi bring in the fresh charge during each cycle and also closes it during the combustion phase.
Cam lift is the distance the cam lobe rises away from the base circle of the camshaft. It is the distance the lifter will move. It is also called "lobe lift."
CALCULATION:
Taking upper radius, R2=5 mm
lower radius, R1=12.5 mm
case-1:
cam lift = 3.5 mm
by using the formula for cam lift,
3.5 = (L-R1)+R2
L = 3.5+7.5
= 11 mm
case-2:
cam lift = 6 mm
by using the formula for cam lift,
3.5 = (L-R1)+R2
L = 6+7.5
= 13.5 mm
SIMULATION:
The simulation was carried out after modelling the following parts.
cam:
Its the source of motion that causes the entire movement. It shows rotational motion and transmits the rotational motion further into the push rod.
push rod:
It acts as the connecting medium between the cam and the rocker arm. It recieves push from the cam, performs linear motion and further transforms it to the rocker arm.
rocker arm:
It is the part that pushes the valve. It recieves push form the push rod and performs repeated motion that results in pushing the valve.
valve:
It is the part that covers the opening of the engine. It is attached with a spring and it opens when the rocker arm pushes it. This mechanism simulates the opening and closing of the opening.
valve root:
It is the part to which the valve is attached to. It acts as a support. There is a spring attached between them and then, they act as the cover for the openings.
assembly:
The moddeled parts were now assembled with the help of coincident and distant mates. They were assembled in such a way that they are only allowed to move in the way we wanted to.
Then, that material was selected as carbon steel.
After making all the constraints for the assembly, it was time for the simulation. First, a motor was assigned at the axis of the cam of 1500 RPM, then solid contact was assigned between all the required parts. Then, a spring was placed between the faces of the valve and the valve root with spring constant 10N/m and free length 45m.
After making these arrangements, the FPS settings was changed to 9000 FPS along with precise contact enabled, as we need to have one frame per degree of rotation of the motor to have a very smooth analysis. Finally, after completing all the arrangements, the motion analysis was begun.
RESULTS AND PLOTS:
case-1 (3.5 mm cam lift):
linear displacement of the push rod:
contact force between the cam and the push rod (magnitude):
contact force between the push rod and the rocker arm (magnitude):
contact force between the rocker arm and the valve (magnitude):
case-2 (6 mm cam lift):
linear displacement of the push rod:
contact force between the cam and the push rod (magnitude):
contact force between the push rod and the rocker arm (magnitude):
contact force between the rocker arm and the valve (magnitude):
contact force between the rocker arm and the valve (X- direction):
reason why the contact force between the Rocker arm and valve varies while measuring with respect to the X direction and measuring with respect to magnitude:
This difference in variation occurs because when we plot the magnitude graph, the plot shows the net force between the two relevant faces. But, when we plot it along X-direction, it plots the force as the force of friction between the same faces. This happens so because, along X-axis, that is the only force that exists between the face.