MBD Simulation on IC Engine Valve Train
Aim: To perform a motion analysis of the IC engine train valve.
Theory: The IC engine valve train is a system that is used to control the operating system of the valves. It happens when the motion of the cam is transmitted to the pushrod and then to the rocker arm from that it is transmitted to the valve.
The role of the valve is that it is used in IC engines that help to control the air/fuel mixture ratio flow.
Let's first discuss the components:
Cam: The cams on a camshaft helps to get the particular kind of displacement based on the rotation and the profile of the cam. It is a mechanical component that is widely used with followers whenever we need to transmit or to convert rotary motion into the to and fro motion of the follower. As the cam rotates, the follower is in contact with the cam, as soon as the shape changes, the displacement starts rising and that motion is transmitted to the rocker arm which will further rotate and transmit motion.
Rocker Arm: It is a kind of oscillating lever which converts the linear displacement of the pushrod to the rotary motion. As the pushrod touches the rocker arm, it will start rising and presses down from the inside which causes the value to get open up. Similarly when it gets to return to its original position due to the action of spring the outer part presses down and the inner part raises up which causes the valve to get closed.
Pushrod: It is also another part of the IC engine valve train, it is a long, slender metal rod fitted in between Cam and rocker arm. The bottom face is in contact with the cam and the upper face is in contact with the rocker arm. As the cam moves due to which linear displacement of pushrod takes place which causes it to get in contact with the rocker arm and push its outer side to rise that leads to the opening of the valve and vice versa for closing the valve. One more thing to add here is that it is receiving motion from the cam and transmitting it to the rocker arm.
Valve & Valve mount
The valve used to control the flow and timing of air and fuel in the case of an IC engine is called a poppet valve.
Valve mount consists of a round hole at the center and having a disc shape ending at the one side.
The rod portion for the poppet valve is an inmate with the stem in the valve mount; it helps to get the motion guided through the working condition. It also acts as a stoppage for the valve and helps to define the amount of movement of the valve.
Final Assembly: Final assembly has been completed via providing various constraints based on their respective motion. Along with that physical dynamics is also used to make contact between valve, rocker arm, pushrod, and cam. Moreover, the spring has been used in between valve and valve stem it is used to close the valve and help to reach back the rocker arm to its original position.
Material Used: Material for all the components is used as Cast carbon Steel.
Objective: Design and perform motion analysis for the Valvetrain assembly for different cam lifts based on given parameters.
Table for cam lift.
|
S.No |
CAM LIFT( mm) |
Speed (rpm) |
Material |
|
1 |
3.5 |
1500 |
Cast carbon Steel |
|
2 |
6 |
1500 |
Cast carbon Steel |
The formula for CAM lift = L- R1+R2
where L is the distance between two centers.
R1 is Radius of Lower circle
R2 is the radius of the upper circle.
For case 1:
D1= 35mm; R1= 17.5mm; CAM LIFT= 3.5mm & D2= 20mm; R2= 10mm
L= 11mm
For case 2:
D1= 35mm; R1= 17.5mm; CAM LIFT= 6 mm & D2= 20mm; R2= 10mm
L= 13.5 mm
Motion Analysis
Now based on the given dimensions, considering both the cases assembly has been created and a motor input of 1500rpm was given to the central axis of the cam. Don't forget to define solid contacts between the bodies.
The spring stiffness is defined as 10N/mm and a free length of 45mm. Frames are defined to 7200 frames per second and enable precise contact.
Results
CASE 1
CAM LIFT IS 3.5mm
- Valve lift plot
- The contact force between Cam and Push Rod
- Contact force between Rocker arm and Push Rod
- The contact force between Rocker arm and Valve.
- The contact force between Rocker arm and Valve in X DIRECTION.
CASE 2
CAM LIFT IS 6.5mm.
- Valve lift plot
- Contact force between Cam and Push Rod
- Contact force between Rocker arm and Push Rod
- Contact force between Rocker arm and Valve.
- Contact force between Rocker arm and Valve in X DIRECTION.
Observation and Conclusion: Valve displacement is higher in the case where cam lift is higher. This shows how the geometry of Cam can affect the opening and closing of valves.
We can observe another thing, that is, the contact force between the rocker arm and value is different in the x-direction plot and in magnitude plot.
The main reason is, the force between the rocker arm and valve will vary positive and in a negative direction because the motion is of to and fro type.
But while calculating the magnitude of the reaction force, it will consider only the magnitude in all the directions which makes its values to be higher than X DIRECTION plot in terms of reaction force.
Animation Link: https://drive.google.com/file/d/1W9Liv3IHjKivN-jkVB_TFVKCgTjThBkg/view?usp=sharing