MBD Simulation on IC Engine Valve Train
IC engine valvle mechanism has been simulated for the both cases of cam lift by changing the design parameters for the cam
The cam was designed as per the formula that relates the camlift(c) and the distance(L) between the centres of the two circles and their radius(r1, r2) respectively.
`c=(L-r1)+r2``; r1>r2`
For both the cases r1=25mm and r2=10mm, there by respective L was found for the corresponding camlift(c).
On assembly of the IC engine valve mechanism, the cam is given a speed of 1500 rpm and the contacts were given to the respective contacts like cam and push rod, push rod and rocker arm, rocker arm and the valve.
Spring function was given between the valve and the valve stem respectively for the cases.
After the similation for each case
- valve lift
- contact forces between cam-push rod, push rod-rocker arm, rocker arm-valve (magnitude and x_direction)
respectively.
Case 1: For a cam lift of 3.5mm at a speed of 1500rpm.
The spring constant was taken as 10 N/mm for the free length of 45mm as per the requirement to keep the assembly in contact. The following are the observation plots from the simulation.
From the above observations and contraints the valve lift was about 2.4mm.
Case 2: For a cam lift of 6mm at a speed of 1500rpm.
The spring constant was taken as 20 N/mm for the free length of 45mm as per the requirement to keep the assembly in contact. The following are the observation plots from the simulation.
From the above observations and contraints the valve lift was about 5mm.
Observation from the above 2 cases:
It is also observed that the force transmitted from cam to pushrod to rocker arm were nearly same with variation due to friction. There was a significant variation of force from rocker arm to valve as major amount of the force was being dampenned by the spring that is between the valve and valve stem i.e. major amount of the force was being used by th espring to get compressed so the amount of force is less on the valve.
Comparing the force magnitude and force in X_direction between the rocker arm and valve, X_direction have shown less force range compared too magnitude as magnitude is sum of all the components and X_direction was one of it. It is also observed that the force direction is reversed for the every half cycle.