MBD Simulation on IC Engine Valve Train
AIM: MBD Simulation on IC Engine Valve Train
INTRODUCTION:
A valve train 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.
A valve train 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.
THEORY:
Components
The valve train consists of all the components responsible for transferring the rotational movement of the camshaft into the opening and closing of the intake and exhaust valves. Typical components are listed below in order from the crankshaft to the valves.
CAMSHAFT
PUSHROD
ROCKER ARM
VALVE
VALVE MOUNT
3 D MODELLING MOTION STUDY SETUP:
Camshaft
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.
Pushrod
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.
Valve float occurs when the valve spring is unable to control the inertia of the valve train at high engine speeds (RPM).
PROCEDURE:
- To run the motion analyis first go to motion study and establish contact between cam and pushrod, pushrodand rocker arm, rocker arm and valve.
- Next, give the rotation to the cam with 1500 RPM
- Set up a linear spring between a valve and the valve mount with the spring stiffness of 10 N/mm and free length 45 mm
- Change the frames to 7200 frames per second and use precise contact.
- Select the entire assembly and assign the material as follows, go to material-edit material and select cast carbon steel and click apply.
- There will be an indication of the material assigned with a change in color of the entire assembly
- Now click the calculation button
- Run the analysis for the reqiured time
Using this we can find valve of ‘L’ for the 2 cases of cam lift:
CASE 1:
Cam Lift=3.5 mm
R1=12.5 mm
R2=5 mm
Therefore, 3.5=(L-12.5) +5
L=3.5+12.5-5
L=11 mm
CONTACT PLOTS:
Cam and Push Rod
Push Rod and Rocker Arm
Rocker Arm and Valve(Magnitude)
Rocker Arm and Valve (X direction)
Valve Displacement
CASE 2:
Cam Lift=6 mm
R1=12.5 mm
R2=5 mm
Therefore, 6=(L-12.5) +5
L=6+12.5-5
L=13.5 mm
CONTACT PLOTS:
Cam and Push Rod
Push Rod and Rocker Arm
Rocker Arm and Valve(Magnitude)
Rocker Arm and Valve (X direction)
Valve Displacement
RESULT AND OBSERVATION:
Explanation:
Case 1: 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 the direction of the force is because of the rocker arm first slides towards the 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.
Case 2: The explanation is same for the cam lift of 6mm, only the difference in the magnitude of the 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 the IC engine
CONCLUSION:
By increasing the CAM lift, valve displacement can be increased.
Valve lift mainly depends on the design of the Cam and Rocker arm
Selection of the suitable spring (free length and spring constant) plays a vital role in the valve lift mechanism.
Vibration can be obtained during retracing valve back to its original position due to spring with lower spring constant selected