MBD Simulation on IC Engine Valve Train

Aim :

To design and perfotm motion analysis of an IC engine valve train of different cam-lifts

Objective:

• Valve Lift.
• The contact force between
  • Cam and Push Rod
  • Pushrod and Rocker Arm
  • Rocker Arm and Valve

Explain why the contact force between the Rocker arm and valve varies while measuring with respect to the X direction and measuring with respect to magnitude.

Introduction:

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 combusion chamber once combustion is completed.

Components:

1. 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.

2. 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.
3. Rocker-arm: 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.
4. 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 valvetrain at high engine speeds (RPM).

Steps :

1. Draw and make each component of valve train assembly in part design.
2. Make two seperate cam one with Cam Lift of 3.5mm and other with cam Lift of 6mm
3. Now assemble all the components with proper constrains.
4. Now select motion analysis and insert a motor with with constant rpm of 1500 attached to axis of cam.
5. Now add a linear spring between valve and valve mount with a spring constant of 10N/mm and free length of 65mm.
6. Now add proper contact consrains between cam, push rod and valve. Now change frames per second to 7200 in motion study properties to obtain frame for each degree of rotation.
7. Now plot results for cam lift, valve lift, contact force between cam and push rod, contact force between push rod and rocker arm ,contact force between rocker am and valve.

3d parts

Rocker arm valve mount

valve pushrod

cam

asemmbly of parts

Governing equation to design cam:

1. For CAM lift = 3.5mm, we assume R1 = 12.5mm & R2 = 6mm

From the cam lift formula, we get L = 10mm

2. For CAM lift = 6mm, we assume R1 = 12.5 mm & R2 = 6mm

From the cam lift formula, we get L = 12.5mm

Motion study

Plots :
case 1 : cam lift 3.5mm,motor speed 1500rpm,frame rate 7200,free length of spring 65 mm,stiffnes of spring 10N/mm^2

case 2 : cam lift 6mm ,motor speed 1500rpm,frame rate 7200,free length of spring 65 mm,stiffnes of spring 10N/mm^2

contact force in xdirection

conclusion :

Contact force between the Rocker arm and valve varies while measuring with respect to the X-direction and measuring with respect to magnitude because if we look at the plot of the X – component of the contact against time, it achieves negative force because the rocker arm slides both forwards and backward during one complete rotation of the CAM and hence the friction force acts in both direction. The magnitude of the contact force between the rocker arm and the valve pushes the valve downwards, but its X- component gives us only the friction force of the rocker arm sliding over the face of the valve head. thus we created the model and assembled them,created motion study and plotted graph on both cases.

Youtube animation link :

https://www.youtube.com/watch?v=FxdeAzdFQs0

Drive link :

https://drive.google.com/drive/folders/13MyClenuxoga_Wgfghn2qcOQO6XRWjym