MBD Simulation on IC Engine Valve Train
INTRODUCTION:
A valve train is a mechanical system that controls operation of the valves in an internal combustion engine, whereby a sequence of components transmits motion throughout the assembly.
A conventional reciprocating internal combustion uses valves to control the flow of the air/fuel mix ture into and out of the combustion chamber.
An OHV or Over Head Valve engine has its valves, well, over the head of the engine. In case of OHV or push-rod systems, there are long rods which have to be pushed by the camshaft lobes to move the valve rockers, which in turn open the valves – thus the name ‘push-rod’. The long rods and the mechanical nature of the push rod system make it heavy and it’s not compatible with engines which run at higher revolutions per minute. Now while OHV is an older design, it has its advantages in terms of simplicity of design, compact packaging and a simpler lubrication system requirement as compared to an OHC system.
The disadvantages, of a push rod system, however, are many. To start with, the engines with an OHV system cannot run very high RPMs and such valve trains are suitable mostly for low engine speed applications such as heavy cruisers. Owing to the heavy components, the noise and friction on such systems is much more than an OHC system. Also, any issues with the camshaft require the entire engine to be opened up, as the camshaft sits inside the engine block, which increases the maintenance effort and cost in case of a breakdown. Finally, OHV engines lend their design well primarily to two-valves per cylinder layout. It’s not that there aren’t any three or four valves per cylinder engines with OHV, but that setup becomes way more complex, and OHC systems offer much more flexibility with multiple valves per cylinders.
PROCEDURE:
After finishing the valve train assembly, go to the solidworks motion.
Select the motor and center axis of the cam and give the input as 1500rpm.
Select the contact forces between the parts and set the material.
Now set it to 7200 frames per second select the precise control.
Now run the motion analysis and find the contact forces for 2 cases.
| Sl.No | CAM Lift (mm) | Speed (RPM) | Material |
| 1 | 3.5 | 1500 | Cast Carbon Steel |
| 2 | 6 | 1500 |
Cast Carbon Steel |
VALVETRAIN ASSEMBLY:
Motion analysis for cam lift 3.5mm:
Valve displacement:
Contact force between cam and push rod:
Contact force between pushrod and rocker arm:
Contact force between rocker arm and valve:
Contact force between rocker arm and valve (x component alone):
Motion analysis for cam lift 6mm:
Valve displacement:
Contact force between cam and push rod:
Contact force between pushrod and rocker arm:
Contact force between rocker arm and valve:
Contact force between rocker arm and valve (x component alone):
CONCLUSION:
Valve Displacement varies w.r.t. the cam lift i.e., in this case the valve displacement increases with 3.5m camlift to 6mm camlift.
The plots obtained, show contact force between the rocker arm and valve varies while measuring with respect to the X direction and measuring with respect to magnitude because the magnitude gives net contact force in all directions. The X direction force gives the contact force only in X direction. This results in reduction of contact force, as seen from the graph.