IC Engine Valve Train

Aim: IC Engine Valve Train Simulation

Objective: Valve Lift Study with respect to CAM Lift 20 and CAM Lift 35

Design:

1) Cam design is based on the cam lift required and is related as:

`L = D - R1 +R2`

where L is cam lift, R1 and R2 and the radii of the circles in cam and D is the distance between their centers.

2) For the assembly to behave as needed the Rocker arm must be dimensioned with respect to the cam lift.

3) Side of the rocker arm supported by the push rod should have a length(a) from the rocker shaft that is corresponding to the cam lift.

`a >= sqrt(l^2+d^2)`

where l is the cam lift and d is the horizontal distance between the pushrod and the rocker shaft

4) Arm length(b) of the rocker side that is in contact with the valve is related to the diameter(c) of the valve head as it has to be in contact with the arm through the entire motion.

`c >= b(1-d/(sqrt(l^2+d^2)))`

5) Using the above equation, for a valve head diameter of 20mm, arm length was calculated such that the parts can be used for both the required cam lifts.

6) 30mm diameter valve head was used in the simulation for safety.

Procedure:

1) The parts were modelled using cast carbon steel and assembled using required contraints.

2) Motion analysis was setup with a 1500 RPM motor at the CAM.

3) The study was conducted at 9000 fps to capture the motion for every degree rotation.

4) Plots for contact forces between the parts and the linear displacement of the valve were generated.

Results:

1) Valve Lift

2) Contact Force Between Push Rod and CAM

3) Contact Force Between Push Rod and Rocker Arm

4) Contact Force Between Rocker Arm and Valve

5) Rocker Arm and Valve Contact Force Magnitude and Contact Force in X direction

Note: The Magnitude represents net contact force between the parts, while the contact force along X direction is the frictional force between the bodies that arises due to the rocker arm sliding over the surface of valve head. The change in direction of the force is because the rocker arm first slides towards origin giving a postive friction force (opposing the motion) and then slides away from the origin giving rise to friction in negative x direction.