MBD Simulation on IC Engine Valve Train

PROJECT REPORT

MBD SIMULATION ON IC ENGINE VALVE TRAIN

INTRODUCTION :

A valvetrain or valve train is a mechanical system that controls operation of the intake and exhaust valves in an internal combustion engine.The intake valves control the flow of air/fuel mixture (or air alone for direct-injected engines) into the combustion chamber, while the exhaust valves control the flow of spent exhaust gasses out of the combusion chamber once combustion is completed. The major components of the valve train are:

1. Cam & CamShaft 2. Pushrod 3. Rocker-Arm 4. Valve and Valve Mountings

OBJECTIVE :

The purpose of this challenge is to model the essential parts of an IC Engine Valve Train and run an MBD simulation on that. Aim to design 3.5mm and 6mm cam profile and study the cam lift phenomenon with contact force between moving parts and contact force of rocker arm and valve in the x-direction.

INPUT PARAMETERS :

Case No.	CAM Lift (mm)	Material	Angular Speed (Rpm)
1.	3.5	Cast Carbon Steel	1500
2.	6	Cast Carbon Steel	1500

CALCULATION :

In orde to design the cams in accordance with the given lift. We have to use the CAM lift formula,

CAM Lift = (L-R1)+R2

where, L = Distance between centres of the two circles

R1 =Radius of the lower circle

R2 = Radius of the upper circle

To obtain the cam dimension for the given cam lift. we do the following calculation

Case 1 : CamLift = 3.5 mm

The Radius of the lower circle (R1) = 10 mm

The Radius of the upper circle (R2) = 3.5 mm

The distance between two centers (L) = 10 mm

CAM Lift = (L-R1)+R2 = (10-10) + 3.5 = 3.5 mm

Case 2 : CamLift = 6 mm

The Radius of the lower circle (R1) = 12.5 mm

The Radius of the upper circle (R2) = 5 mm

The distance between two centers (L) = 13.5 mm

CAM Lift = (L-R1)+R2 = (13.5-12.5) + 5 = 6 mm

PROCEDURE :

FIRST, From given cam lift and design and do calculation for cam profile for precise motion.

SECOND, Model all the components of the IC Valve train in the separate part file.

THIRD, Assemble all the parts with precise distance to obtain required motion. Make sure that the contraints and mates assign correctly.

FOURTH, Assign material equal to cast carbon steel property to each part.

FIFTH, To resist and to retract valve in its original position, add a spring between the valve and valve mount with free length 45mm and stiffness 10 N /mm

SIXTH, Evaluate the simulation at 1200 frame rate to measure the accurate motion of valve train.

SEVENTH, Do the post processing for the study of MBD simulation on IC Engine valve train.

EIGTH, Obtain the following Graphs for both cases,

1. Valve displacement
2. The contact force between cam and push rod
3. The contact force between the push rod and rocker arm
4. The contact force between rocker arm and valve
5. The contact force between valve and rocker arm in the x-direction

CAD MODELS :

1. CAM for lift = 3.5 mm

2. CAM for lift = 6 mm

3. Push-Rod

4. Rocker-Arm

5. Engine Valve

6. Engine Mount

7. Full Valve train Assembly

RESULTS :

Case 1 : CamLift = 3.5 mm

Plot 1 : Valve Lift

Plot 2 : The contact force between cam and push rod

Plot 3 : The contact force between the push rod and rocker arm

Plot 4 : The contact force between rocker arm and valve.

Plot 5 : The contact force between valve and rocker arm in the x-direction

Case 2 : CamLift = 6 mm

Plot 1 : Valve Lift

Plot 2 : The contact force between cam and push rod

Plot 3 : The contact force between the push rod and rocker arm

Plot 4 : The contact force between rocker arm and valve.

Plot 5 : The contact force between valve and rocker arm in the x-direction

CONCLUSION :

1. 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 is because w.r.t magnitude the force is positive i.e, it gives the modulus of the net force acting. While w.r.t. X- direction the magnitude of the force is negative. This is because of the fact that in line contact between the valve and the rocker arm are due to the action of force applied by spring which opposes the rocker arm movement means resist to move the valve in a downward direction. Due to the resistant movement of valve it tends to push back valve to its initial position. This led to develop a negative contact force between the rocker arm and the valve in the X-direction.

2. The valve oscillate and lift differ when cam designs are modified depends on the Cam geometry.