MBD Simulation on IC Engine Valve Train

INTRODUCTION:

The valve train consists of the valves and a mechanism that opens and closes them. The opening and closing system is called a camshaft. The cams on the shaft activate the valves directly or through a very short linkage.

At the bottom ends the pushrods are fitted with lifters, either solid or hydraulic, upon which the camshaft, located within the cylinder block, makes contact. The camshaft pushes on the lifter, which pushes on the pushrod, which pushes on the rocker arm, which rotates and pushes down on the valve.

OBJECTIVE:

To perform the Motion Analysis of IC Engine Valve Train Mechanism by obtaining the following plots:

1. The Linear Displacement of
   • Valve Lift.
2. The Contact force between
   • Cam and Push Rod.
   • Pushrod and Rocker Arm.
   • Rocker Arm and Valve.
3. The Contact force between
   • Rocker arm and valve varies while measuring with respect to the X direction.

Now Running the Motion Study for obtaining the above plots with the below parameters:

CAM Lift (mm)	Speed (RPM)	Material
3.5	1500	Cast Carbon Steel
6	1500	Cast Carbon Steel

PROCEDURE:

3D Models:

CAM:

Generally, the CAM is designed by coinciding the smaller circle with bigger circle which is as follows:

Since the CAM LIFT is given, by using the CAM Lift formula to find out the respective Distance between two centres (L) for 3.5mm CAM LIFT and 6mm CAM LIFT. The CAM Lift formula is been provided below:

CAM LIFT FORMULA:

A sample CAM Lift is been provided below:

CAM Lift = (L-R1) + R2

• Diameter of lower circle (D1) - 35 mm
• Diameter of upper circle (D2) - 20 mm
• Distance between two centres (L) - 30 mm

For 3.5mm CAM Lift:

Since the Cam Lift is been provided as 3.5mm, we need to calculate the Distance between two centres (L), by using the above formula, we arrange and get the formula for L as:

L = (CAM Lift – R2) + R1

= (3.5 – 5) + 12.5

= -1.5 + 12.5

= 11mm

For 6mm CAM Lift:

Since the Cam Lift is been provided as 6mm, we need to calculate the Distance between two centres (L), by using the above formula, we arrange and get the formula for L as:

L = (CAM Lift – R2) + R1

= (6 – 5) + 12.5

= 1 + 12.5

= 13.5mm

PUSH ROD:

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

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.

VALVE STEM AND VALVE:

Most modern engines use poppet valves type, although sleeve valves, slide valves and rotary valves have also been used at times. valve float occurs when the valve spring is unable to control the inertia of the valve train at high engine speeds (RPM). Poppet valves are typically opened by the camshaft lobe or rocker arm, and closed by a coiled spring called a valve spring.

ASSEMBLY:

For 3.5mm CAM Lift:

For 6mm CAM Lift:

Plots:

For 3.5mm CAM Lift:

3.5mm | Linear Displacement | Valve Lift

3.5mm CAM Lift |Contact Force | CAM & Push Rod

3.5mm CAM Lift | Contact Force | Push Rod & Rocker Arm

3.5mm CAM Lift | Contact Force | Rocker Arm & Valve

3.5mm CAM Lift | Contact Force | Rocker arm & Valve| X direction

For 6mm CAM Lift:

6mm CAM Lift | Linear Displacement | Valve Lift

6mm CAM Lift | Contact Force | CAM & Push Rod

6mm CAM Lift | Contact Force | Push Rod & Rocker Arm

6mm CAM Lift | Contact Force | Rocker Arm & Valve

6mm CAM Lift | Contact Force | Rocker Arm & Valve | X direction

RESULT & CONCLUSION:

Rocker Arm & Valve | Magnitude

The contact force between the Rocker Arm and Valve varies while measuring with respect to magnitude provides the positive valve due to the net force acting on it. This is because the contact line performs to and fro motion in vertical direction which negates the need for measuring the direction.

Rocker Arm & Valve | X-Direction

In case of measuring the rocker arm and valve with respect to X-direction, it results in negative valve due to the frictional force that is presented. This is because the X-direction depicts negative values due to frictional contact.

Drive Link for Part files & Assembly with the excel: IC Engine Valve Train