MBD Simulation on IC Engine Valve Train

AIM: Run a motion analysis for IC Engine Valve Train Assembly.

OBJECTIVES:

• Create 3D models for all the components.
• Assemble all the parts.
• Perform motion analysis by rotating the crank at 1500 rpm for 3 different conditions.
• Obtain Valve Lift.
• Obtain contact force between Cam and Push Rod, Pushrod and Rocker Arm, Rocker Arm and Valve (respect to x direction and magnitude)

ENGINE PISTON ASSEMBLY

A valve train is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine by transferring the rotational movement of the camshaft into the opening and closing of the intake and exhaust valves. The intake valves control the flow of air-fuel mixture into the combustion chamber, while the exhaust valves control the flow of spent exhaust gasses out of the combustion chamber once combustion is completed.

COMPONENTS OF VALVE TRAIN

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.

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.

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.

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.

DIFFERENT CONDITIONS

Sr. No	CAM Lift (mm)	Speed (RPM)	Material
1	3.5	1500	Cast Carbon Steel
2	6	1500	Cast Carbon Steel

 

CAM Lift = (L-R₁) + R₂

L= CAM Lift - R₂ + R₁

In our case R₁=12.5 mm and R₂= 5 mm

For 3.5 mm cam lift

L= 3.5-5+12.5 =11 mm

For 6 mm cam lift

L= 6-5+12.5 =13.5 mm

STEP-WISE PROCEDURE:

• First, we have to create crank, push rod, rocker arm, valve, valve mount in front plane.

• Now we have to assemble all the components with appropriate constrain in front plane.

• For proper position we move the valve with the help of physical dynamics.
• Give the material to the components Cast carbon steel.
• Then go to motion analysis and give the contact between crank and Push rod, Push rod and rocker arm, rocker arm and valve.
• Give the motor to crank and set the speed 1500 rpm.
• To capture every crank angle position set the frames per second to 9000.
• For reverse motion of the valve we have to attach spring between valve and valve mount.
• Then calculate the motion data and plot the graph for the linear displacement of valve called valve lift.
• Plot the graph for contact force between Cam and Push Rod, Pushrod and Rocker Arm, Rocker Arm and Valve (respect to x direction and magnitude).
• Then we have to repeat the motion study after modify the crank for 6 mm lift.

OUTPUT PLOTS

Case 1: Perform motion analysis for 3.5 mm Cam-lift.

For this case spring constant is 10 N/mm.

Valve lift

Contact force between crank and push rod

Contact force between push rod and rocker arm

Contact force between rocker arm and valve respect to magnitude

Contact force between rocker arm and valve respect to x-direction

Case 2: Perform motion analysis for 6 mm Cam-lift.

For this case spring constant is 20 N/mm.

Valve lift

Contact force between crank and push rod

Contact force between push rod and rocker arm

Contact force between rocker arm and valve respect to magnitude

Contact force between rocker arm and valve respect to x-direction

CONCLUSION

• As we increase the cam-lift the amount of contact force is increased for all the graph.
• In the graph for contact force between valve and rocker arm respect to x direction is also in negative direction because of the friction force and may be due to the spring force.
• 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 magnitude is the result force of all the X, Y and Z direction. So, it is differing from only in x direction.
• As per calculation respect to rocker arm ratio which is 2.5 in or case, valve lift is 2.5 times cam lift. In the 3.5 mm cam lift case, valve lift will be 8.75 mm and valve lift will be 15 mm in 6 mm cam lift case but we can not get this value due to the spring effect.

Google drive link for part and assembly

https://drive.google.com/drive/folders/1hf_ta052Vx4s6QteEBtlfdKDljTHcolJ?usp=sharing