MBD Simulation on IC Engine Valve Train
Aim/Objective: MBD Simulation on IC Engine Valve Train
Theory:
Valve Train:
A valvetrain or valve train is a mechanical system that controls operation of the intake and exhaust valves in an internal combustion engine. The intake valves control the flow of air/fuel mixture (or air alone for direct-injected engines) into the combustion chamber, while the exhaust valves control the flow of spent exhaust gasses out of the combustion chamber once combustion is completed.
Cam Shaft:
The timing and lift profile of the valve opening events are controlled by the camshaft, through use of a carefully shaped lobe on a rotating shaft. The camshaft is driven by the crankshaft and— in the case of a four-stroke engine— rotates at half the speed of the crankshaft.
Motion is transferred from the crankshaft to the camshaft most commonly by a rubber timing belt, a metallic timing chain or a set of gears.
Push Rod:
Pushrods are long, slender metal rods that are used in overhead valve engines to transfer motion from the camshaft (located in the engine block) to the valves (located in the cylinder head). The bottom end of a pushrod is fitted with a lifter, upon which the camshaft makes contact. The camshaft lobe moves the lifter upwards, which moves the pushrod. The top end of the lifter pushes on the rocker arm, which opens the valve.
Rocker Arm/ Bucket Tappet:
Depending on the design used, the valves are actuated by a rocker arm, finger or bucket tappet. Overhead camshaft engines use fingers or bucket tappets, upon which the cam lobes contact. Overhead valve engines use rocker arms, which are actuated by a pushrod and pivot on a shaft or individual ball studs in order to actuate the valves.
Valves:
Most modern engines use poppet valves type, although sleeve valves, slide valves and rotary valves have also been used at times. Poppet valves are typically opened by the camshaft lobe or rocker arm and closed by a coiled spring called a valve spring.
Conditions/Parameters:
| Sl.No | CAM Lift (mm) | Speed (RPM) | Material |
| 1 | 3.5 | 1500 | Cast Carbon Steel |
| 2 | 6 | 1500 |
Cast Carbon Steel |
Formulation:
3d Model:
Graphs/Plots:
CASE 01:
CAM LIFT = 3.5MM
THE DISTANCE BETWEEN TWO CENTERS(L)
L = 11 MM
CAM AND PUSHROD :
PUSHROD AND ROCKER ARM:
ROCKER ARM AND VALVE:
ROCKER ARM AND VALVE (X-DIRECTION):
CASE 02:
CAM LIFT = 6 MM
THE DISTANCE BETWEEN TWO CENTERS(L)
L = 13.5 MM
CAM AND PUSHROD :
PUSHROD AND ROCKER ARM:
ROCKER ARM AND VALVE:
ROCKER ARM AND VALVE (X-DIRECTION):
Observation/Result:
The Magnitude represents net contact force between the parts, while the contact force along the X direction is the frictional force between the bodies that arise due to the rocker arm sliding over the surface of the valve head.The change in direction of the force is because the rocker arm first slides towards origin giving a positive friction force (opposing the motion) and then slides away from the origin giving rise to friction in the negative x-direction. Therefore the plots are opposite to each other.The explanation is same for the cam lift of 6 mm, only it differs in magnitude of contact forces. The movement in this case is quite smoother compared to the cam lift of 3.5 mm as observed. As the cam lift increases more air-fuel mixture can enter into the cylinder of IC engine.
Animation:
Youtube link: