MBD Simulation on IC Engine Valve Train

Objective

1) To Plot

• Valve Lift.
• The contact force between
  • Cam and Push Rod
  • Pushrod and Rocker Arm
  • Rocker Arm and Valve

2) Explain 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.

Theory

IC valve train is an essential part of IC engine as it controls opening and closing of valves. The valve train consists of a Cam , Push rod, rocker Arm , valve and a spring attached between valve and valve mount.

Cam lift is given by

Fig.1. IC engine Valve Train

Procedure

1. Draw and make each component of valve train assembly in part design. Make two seperate cam;one with Cam Lift of 3.5mm and other with cam Lift of 6mm. Now assemble all the components with proper constrains.
2. Now select motion analysis and insert a motor with with constant rpm of 1500 attached to axis of cam. Now add a linear spring between valve and valve mount with a spring constant of 10N/mm and free length of 60mm. Now add proper contact consrains between cam, push rod and valve. Now change frames per second to 9000 in motion study properties to obtain frame for each degree of rotation.
3. Now plot results for cam lift, valve lift, contact force between cam and push rod, contact force between push rod and rocker arm ,contact force between rocker am and valve.

Results & Plots

1. For Cam Lift of 3.5 mm

Fig2. Linear Displacement of pushrod with maximum displacement of 3.5mm

Fig3. Linear Displacement of valve with maximum displacement of 0.9 mm

Fig4. Contact Force between cam and push rod

Fig5. Contact Force between push rod and Rocker arm

Fig6. Contact Force between Rocker arm and Valve (magnitude)

Fig7. Contact Force between Rocker arm and Valve (X direcion)

2. For Cam Lift of 6 mm

Fig8. Linear Displacement of pushrod with maximum displacement of 6 mm

Fig9. Linear Displacement of valve with maximum displacement of 2.1 mm

Fig10. Contact Force between Cam and push rod

Fig11. Contact Force between push rod and Rocker arm

Fig12. Contact Force between Rocker Arm and Valve

Animations

Animation1. Simulation of IC engine valve train with cam lift of 3.5mm

Animation2. Simulation of IC engine valve train with cam lift of 6mm

Animation3. Effect of low compresion in spring( push rod leaves contact with cam)

Conclusion

1) Valve lift for cam lift of 3.5 mm is 0.9 mm

2) Valve lift for cam lift of 6 mm is 2.1 mm

3) Valve lift is less than that of cam lift and it depends upon the design of mechanism.

4) Contact force is not constant throughout due to absence of damper in system, which causes some unwanted vibrations in system.

5) Contact force between the Rocker arm and valve varies while measuring with respect to the X direction and measuring with respect to magnitude due to varing contact point and line of action of contact force between rocker arm and valve. Due to this reason a reaction force perpendicular to valve motion develops which causes losses in system and produces sound.

6) Free length of spring should be carefully selected to maintain a precmpression in spring. This precompresion should be sufficient to keep continuous contact between cam and push rod. (refer animation 3)

References

1)http://www.ijirset.com/upload/2017/tapsa/4_auto_005.PDF