MBD IC Engine Train Valve Mechanism

AIM:

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

OBJECTIVES:

1. To understand the working of an IC engine valve train
2. To understand how different cam-lifts can affect the working of the valve train
3. To analyze the above using SOLIDWORKS

SIMULATION CASES:

S. NO	CAM LIFT (mm)	SPEED (RPM)	MATERIAL
CASE 1	3.5	1500	Cast Carbon Steel
CASE 2	6	1500	Cast Carbon Steel

THEORY:

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 LIFT FORMULA:

CAM Lift can be derived from the formula given below

• The diameter of lower circle (D1)
• The diameter of upper circle (D2)
• The distance between two centres (L)

CAM LIFT = (L - R1) + R2

For CAM-Lift =3.5mm, R1 = 6.5 mm and R2 = 3.5 mm

L = 6.5 mm

For CAM-lift = 6 mm, R1 = 10mm and R2 = 6.5 mm

L = 10 mm

OBSERVATIONS & PLOTS:

CASE 1: 3.5 MM LIFT

Animation: https://youtu.be/85p-4Odn3KQ

• Valve Lift

The contact force between :

Cam and Push Rod

Pushrod and Rocker Arm

Rocker Arm and Valve:

• Considering Magnitude:

• Considering X-component of the contact force:

CASE 2: 6 MM LIFT

Animation: https://youtu.be/257CTEKNWpQ

Valve Lift

The contact force between :

Cam and Push Rod

Pushrod and Rocker Arm

Rocker Arm and Valve

• Considering Magnitude:

• Considering X-component of the contact force:

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.

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.

Conclusion:

• The contact forces b/w each component and linear displacement of the valve for the cam lift of 6mm is ‘larger than’ the cam lift of 3.5mm. This shows that CAM geometry affects the amount of opening of the valve through which the mixture enters the cylinder.
• The linear displacement of the valve is greater than the lift produced by the CAM as the moment arm towards the valve is greater than that towards the pushrod.
• In the plot of contact forces against time for rocking arm and the valve, a minimum force is always present due to the initial compressed state of the spring.
• The contact forces are at their peaks when the CAM lobe is at its topmost position.