MBD Simulation on IC Engine Valve Train

MBD Simulation of IC Engine Valve Train:-

It's a detailed report on the MBD Simulation of IC Engine Valve Train. It is the mechanism used in IC Engines to control the opening and closing of various valves for efficient fuel combustion. The Cam in this mechanism is mounted on camshaft which is driven by the crankshaft. As the Cam rotates along with camshaft, it drives the Pushrod in the vertical direction which further operates the Rocker Arm. The Rocker Arm pushes the valve which opens in the combustion chamber. The Cam profile is preferably the most important design variable in the system for valve timings.

Simulation Specifications:-

The input is provided to Cam as constant rpm. Various outputs are achieved including valve displacement and contact forces.

Input rpm = 1500

Angular velocity of Cam = 2*3.14*1500/60

= 157 rad/sec

= 9000 deg/sec

Components material = Cast carbon steel

Spring constant = 15 N/mm

Free length of spring =45 mm

Initial compression = 10 mm

Initil length of spring = 45-10 = 35 mm

Contact material used = Steel (Dry)

Frames per second selection = 9000

Precise contact selection = On

Cam lift formula-

We have taken D1 as 25 mm and D2 as 10 mm

for case 01,

Distance between the circles is = Cam lift + R1 - R2

= 11 mm

for case 02,

Distance between the circles is = 13.5 mm

Case 01 ( 3.5 mm Cam Lift):-

In this case, a 3.5 mm cam lift is provided in the cam design. Various plots are plotted below-

Displacement of valve in Y-direction (vertical)-

Displacement varies according to the cam profile. Most of the cam profile is circular so most of the time valve remains at a particular position.

Contact Force between the cam and push rod-

In this graph as well, most of the time contact force remains constant due to the fact that most of the cam profile is circular ( hence no change in pushrod displacement). But just after the maximum values, the contact force suddenly becomes zero because the pushrod may suddenly lost contact with the cam. Some contact force is always there because the spring is initially in some compression.

Contact Force between Pushrod and Rocker arm-

Almost same kind of results is obtained for the contact between pushrod and rocker arm for the previous reasons. Mostly, the graph remains flat.

Contact Force between Rocker Arm and Valve (magnitude wise & X-Direction)-

Explanation:-

As we observe the graphs between rocker arm and valve for both magnitude-wise and in X-direction, we see some differences in graphs. The magnitude graph has all values as positive (which is obvious) and most of the time some constant value due to the cam profile ( initial spring compression). But in the case of force in X-Direction, we have both positive and negative values of force because this force is nothing but the friction. Rocker arm rotates in both directions during the motion and hence the direction of friction also changes.

Case 02 (6mm cam lift):-

In this case, the cam lift is 6 mm. All the results are plotted below-

Displacement of the valve in Y-Direction-

Contact Force between RockerArm and Pushrod-

Contact Force between Rocker Arm & Valve ( Magnitude and X-Direction)-

Summary and Conclusion:-

Results are plotted for both cases. In case 02, the values are slightly higher which can be understood by the fact that the cam lift is a bit greater than the previous case which results in more compression of springs hence in an increase in contact forces. Also, bigger sizes producing larger displacements.

The spring is in slight compression initially, so there is always some contact force acting between components.