MBD Simulation on IC Engine Valve Train

Objectives :-

• To create a model of the CAM and its associated parts for the IC Engine valve train then run an MBD simulation on that.
• Run the simulation using the below parameters

• Obtain the plot of
  
  • Valve Lift. 
  • The contact force between 
    • Cam and Push Rod
    • Pushrod and Rocker Arm
    • Rocker Arm and Valve

Introduction :

   A 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 used in Valve train mechanism :

   The valvetrain 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.

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.

2) Pushrods

Pushrods are long, slender metal rods that are used in overhead valve engines to transfer motion from the camshaft to the valves.

3) Rocker Arm

The valves are actuated by a rocker arm. 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) Valve

Most modern engines use popet valves type, although sleeve valves, slide valves and rotatry 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.

5) Valve mount

Valve mount use to support the valve to move in correct direction.

Calculation for Cam Lift :

Given formula for calculating the cam lift

Cam lift for Case I = 3.5 mm

Cam lift = (L-R1)+R2

By the above fig,

• R1 = 10 mm
• R2 = 5 mm
• L = 8.50 mm

So, Cam lift = (8.5 - 10) + 5

                  = 3.5 mm

Cam lift for Case II = 3.5 mm

Cam lift = (L-R1)+R2

By the above fig,

• R1 = 10 mm
• R2 = 5 mm
• L = 11 mm

So, Cam lift = (11 - 10) + 5

                  = 6 mm

Simulation setup :

• Rotation of Cam in clockwise direction.
• Speed of crank is 1500 RPM
• A Spring attached between valve and Valve mount.
• Free length of spring is given as 52 mm and spring constant as 10 N/mm.
• Material used to calculate contact force between two matting component is Steel(Dry).

Assembly and result :-

Case I : Cam lift 3.5 mm

Fig : Assembly of valve train

Fig : Linear displacement of Push rod

Fig : Linear displacement of Valve

Fig : Contact force between Cam and Push rod

Fig : Contact force between Push rod and Rocker arm

Fig : Contact force between Rocker arm and Valve (Along Magnitude)

Fig : Contact force between Rocker arm and Valve (Along x-axis)

Case II : Cam lift 6 mm

Fig : Assembly of valve train

Fig : Linear displacement of Push rod

Fig : Linear displacement of Valve

Fig : Contact force between Cam and Push rod

Fig : Contact force between Push rod and Rocker arm

Fig : Contact force between Rocker arm and Valve (Along Magnitude)

Fig : Contact force between Rocker arm and Valve (Along x-axis)

Conclusions :-

• For the 1st case as we give cam lift 3.5 mm, the valve displacement is around 1 mm but when we increases the cam lift to 6 mm, we got valve displacement of around 3.1 mm.
• From both the case 1&2 contact force between Push rod and Cam, and Push rod and Rocker Arm are approximately same.
• When comparing the contact forces between case 1&2 the contact forces is much more in case 2 then case 1. It's because the cam lift is more in case 2 so the force required compress the spring is more.

Q) 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.

The 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 contact force of Rocker arm and valve along x-axis is frictional force that cause by the sliding of Rocker arm on the valve but the contact force of Rocker arm and valve along magnitude consider magnitude of both the friction force occuring in x direction and the force along the y direction to move the valve.

Reference:- 

• projects.skill-lync.com
• www.google.com
• https://en.wikipedia.org/