MBD Simulation on IC Engine Valve Train - SolidWorks

MBD Simulation on IC Engine Valve Train - SolidWorks

1. AIM:

To model, assemble and perform MBD Simulation on IC Engine Valve Train

2. INTRODUCTION:

- A valve train is a mechanical system that controls operation of the intake and exhaust valves in an internal combustion engine.

- A cam is a profiled object whose job is to push the pushrod at regular intervals of time decided by the perimeter and profile itself.

- A Pushrod is a long, slender metal rod that is used in overhead valve engines to transfer motion from the camshaft (located in the engine block) to the valves (located in the cylinder head).

- A rocker arm is an oscillating lever that conveys radial movement from the cam lobe into linear movement at the poppet valve to open it.

- A valve is a structure which allows mixture into and out of the cylinder with the help of valve spring.

3. OBJECTIVES:

To run the simulation for these cases:

Sl.No	CAM Lift (mm)	Speed (RPM)	Material
1	3.5	1500	Cast Carbon Steel
2	6	1500	Cast Carbon Steel

Obtain the following plots:

-Valve Lift.

-The contact force between: Cam and Push Rod, Pushrod and Rocker Arm, Rocker Arm and Valve.

Cam lift formula:

For obtaining 3.5mm and 6mm cam lifts, change the radius of the circles accordingly to get desired lifts.

for 3.5mm, set diameter of upper circle to 7mm because L-R1 is 0.

for 6mm, set diameter of upper circle to 12mm because L-R1 is 0.

4. FLOW OF THE PROJECT:

1. Create 3D CAD models.
2. Assemble the CAD models using proper constraints.
3. Use the assembly in motion analysis and set-up the motion parameters like rpm, material, contacts etc.
4. Run the calculations.
5. Save animation and plot the required graph.
6. Switch to other case and repeat calculations.
7. Save the animations.
8. Plot graphs.

5. MOTION STUDY SETUP:

1. Initially, the 3D CAD models for different parts of the piston assembly are created in Solidworks.
2. Assembly with proper constraints is then done and basic motion is checked using drag mouse technique.
3. A new motion study having type as Motion Analysis was selected.
4. In analysis settings, precise contact is turned ON and frames per second is set to 9000 as 1500RPM translates into 9000 deg/sec and we need to capture every single degree in our calculations.
5. Contacts between every touching component is defined with material as steel(dry).
6. Also, material of the indicidual components is set to cast carbon steel.
7. The cam is set to the RPM as defined in first case and then subsequent cases.
8. Gravity is turned on in the downward direction.
9. Spring is set with sufficient stiffness in between valve stem and valve to ensure valve return after opening the seat.

6. OBSERVATION, RESULT AND CONCLUSION:

Case 1:

Case 2:

Conclusion:

- After comparing the plots from both cases, we can deduce that:

1. Valve lift is directly proportional to cam lift. If cam lift is greater, the valve lift is also greater.
2. Contact forces are inversely proportional to the cam lift. If cam lift is greater, the contact forces between various parts of the valve train is lower. We can see that clearly from the plots.

- 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?

Ans. The contact force between Rocker arm and the valve is not uni-directional. It acts along X as well as Y axis. Now to talk about X axis, initially, the valve is at rest. After some time, as the rocker arm pushes the valve downward, this downward pushing is due to pivoting of the rocker arm at the left side of the valve, i.e the motion is clockwise. So while the valve is getting pushed downward the rocker arm is getting moved from down side to left side (rotating). Thus as it is moving to left side circularly, the friction should act against it in the right side.

Similarly while returning, the motion of rocker arm is anti-clockwise thus friction acts to the left side thus reversing the direction of contact force. So in the graph we can see that positive force is while pushing valve down while negative force is while returning.

There is no negative force in the magnitude plot because magnitudes do not take direction into account thus everything is positive including forces of all directions.