MBD Simulation on IC Engine Valve Train

I.C Engine Valve Mechanism Motion Analysis:

Aim: To create CAD model for Valve mechanism used in I.C Engines and create motion analysis for the valve mechanism. Also, to plot graphs for contact forces between the contacts of touching.

Introduction: A valve mechanism is widely used in automotive engine system. The main components of the valve mechanism are valve, rocker arm, spring , CAM, pushrod and the valve mount or valve seat. The basic working idea behind this mechanism is that CAM is rotated by the crankshaft of the engine which rotates twice to that of crankshaft. The rotary motion of the CAM in turn moves the pushrod and pushrod moves the the rocker arm and rocker arm in turn moves down the valve supported by spring. So, the valve opens and closes due to spring action.

Steps taken in CAD Models:

1. SolidWorks was opened. Unit adjusted to MMGS.
2. For CAM model, two circles are made such that the center of other circle coincides with the periphery of the other circle.Appropriate constraints-vertical are applied. With the help of line tool tangents were made between the circles on either sides.
3. The CAM sketch was mid-plane extruded to appropriate dimensions.
4. For Valve mount or seat, line comands was used and appropriate distance was specified between the axis of revolution and the sketch. After defining the sketch, it was then revolved.
5. For valve stem commands used were line, 3-point arc and revolve. Within the diagram appropriate constraints were applied.
6. Pushrod was modeled by using line command, 3-point arc and then revolve feature was used.
7. Rocker arm was modeled by using line, circle and 3-point arc tool. Appropriate horizontal and tangent constraints were applied. It was then extruded mid-plane.

Considerations and Assumptions:

1. Formula for calulating length of the centres of circle was refered from the following figure:
2. From CAM lift of 3.5mm, the length of the centres of the circle came around 11mm.
3. From CAM lift of 6mm, the length of the centres of the circle came around 13.5mm.
4. All the materials for the simulation process was selected as “Cast Carbon Steel”.
5. CAM input motor was adjusted to 1500 RPM with 7200fps.
6. Spring Constant assumed as 10 unit and free length as 45mm.

CAD Models:

CAM (3.5mm Lift):

Push Rod:

Rocker Arm:

Valve:

Valve Mount or seat:

CAM (6mm Lift):

1. Observations:

   CAM Lift = 3.5mm

   1. Contact force between CAM and Pushrod:
   2. Contact force between Pushrod and Rocker Arm:
   3. Contact force between Rocker Arm and Valve:
   4. Contact force between Rocker Arm and Valve in X-direction:
3. CAM Lift = 6mm
5. 1. Contact force between CAM and Pushrod:
7. 2. Contact force between Pushrod and Rocker Arm:
9. 3. Contact force between Rocker Arm and Valve:
11. 4. Contact force between Rocker Arm and Valve in X-direction:

13. Inferences:

    The motion analysis was carried out for 0.5 seconds.

    • For CAM Lift of 3.5mm
    1. F (CAM and Push Rod) = 170. 199 N.
    2. F (Pushrod and Rocker Arm) = 171.99 N.
    3. F (Rocker Arm and Valve) = 72.77 N.
    4. F (Rocker Arm and Valve in X direction) = 20.914 N.
    • For CAM Lift of 6mm
    1. F (CAM and Push Rod) = 9.432E – 18 N.
    2. F (Pushrod and Rocker Arm) = 9.54 N.
    3. F (Rocker Arm and Valve) = 99.403 N.
    4. F (Rocker Arm and Valve in X direction) = 24.07 N.

• Uniform graphs obtained in all cases.
• The graph for contact forces between Rocker Arm and Valve in magnitude and the same graph in X direction was a different as the magnitude graph gave results as a resultant of forces in X, Y and Z direction.

Conclusion:

• On comparing the results obtained from the motion analysis graph that was run for 0.5 seconds for both cam lift of 3.5mm and 6mm, more contact forces were observed for 3.5mm Cam Lift.
• The graph for contact forces between Rocker Arm and Valve in magnitude and the same graph in X direction was a different as the magnitude graph gave results as a resultant of forces in X, Y and Z direction.