MBD Simulation on IC Engine Valve Train

AIM: To do multibody dynamics (MBD) simulation on I. C. Engine Valve Train using SOLIDWORKS.

OBJECTIVE:

• To design parts like cam, push rod, rocker arm, valve, and valve stem.
• To create an assembly using all the parts.
• To do motion analysis in the cases mentioned below.
• To obtained plot for linear displacement of valve, contact force between cam and push rod, contact force between push rod and rocker arm, and contact force between rocker arm and valve. Plot is obtained in the following cases:

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

THEORY:

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 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:

The valve train 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. Typical components are listed below in order from the crankshaft to the valves.

• 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. Motion is transferred from the crankshaft to the camshaft most commonly by a timing belt or a set of gears.
• Pushrod: 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: 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 in order to actuate the valves.
• Valves: 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 valve train at high speeds.

Motion studies are graphical simulations of motion for assembly models. Motion studies do not change an assembly model or properties. They simulate and animate the motion we prescribe for a model. By using Solidworks mates to restrict the motion of components in an assembly when we model motion. From motion studies, motion analysis can also be done for accurately simulating and analyzing the effects of motion elements. It can also be used to plot simulation results for further analysis.

PROCEDURE:

• Calculate the distance between the centers from Cam lift Formula for creating a 3D model of cam.

CASE 1: Given: Cam Lift (C)= 3.5 mm Diameter of lower circle (D1)= 25 mm Diameter of upper circle (D2)= 10 mm Distance between the two circles = C – R2 + R1 = 3.5 – 5 + 12.5 = 11 mm

CASE 2: Given: Cam Lift (C)= 6 mm Diameter of lower circle (D1)= 25 mm Diameter of upper circle (D2)= 10 mm Distance between the two circles = C – R2 + R1 = 6 – 5 + 12.5 = 13.5 mm

• After that create 3D models of pushrod, rocker arm, valve, and valve stem and save them separately. Give all of them a material of Cat Carbon Steel.

• After creating all the parts separately, assembly is created using all the parts. After exporting all the parts in Solidworks, the first part is made floating by right clicking on the first part and then selecting float option. Then select temporary axis visible option and then use appropriate mate option to constrain a part.
• The first assembly created is with a cam lift of 3.5 mm. Now do the motion analysis of this case of assembly, by providing a motor at the axis of the cam of 1500 RPM constant speed. Now make contact appropriately by keeping the material of all the parts same, i.e., Steel (dry). After this set a spring between the valve and valve stem by keeping the spring constant as 10 N/mm. After this set the frames to 9000 FPS and also use the precise contact option. Then get plots on linear displacement of valve, contact force between valve and rocker arm, contact force between valve and rocker arm in x-direction, contact force between rocker arm and pushrod, contact force between pushrod and cam, export it to excel sheet, also create an animation.

• Now the second assembly created is with a cam lift of 6 mm. In this case edit the cam profile by keeping the distance between the two circles as 13.5 mm. Now do the motion analysis of this case as mentioned above and also get plots on linear displacement of valve, contact force between valve and rocker arm, contact force between valve and rocker arm in x-direction, contact force between rocker arm and pushrod, contact force between pushrod and cam, export it to excel sheet, also create an animation.

PLOTS AND ANIMATIONS:

• Cam Lift of 3.5 mm

ANIMATION: Valve Train with cam lift of 3.5 mm

• Cam Lift of 6mm

ANIMATION: Valve Train with cam lift of 6 mm

CONCLUSIONS:

• The graph between Pushrod and Cam shows the contact force between them. Graphs are plot for the cases, for 3.5 mm cam lift and for 6 mm cam lift. The contact force for 3.5 mm cam lift ranges from 0 N to 4700 N and for 6 mm cam lift it ranges from 0 N to 16000 N. Some forces due to friction are also generated during the motion.
• The graph between Pushrod and Rocker Arm shows the contact force between them. Graphs are plot for the cases, 3.5 mm cam lift and for 6 mm cam lift. The contact force for 3.5 mm lift ranges from 0 N to 4700 N and for 6 mm cam lift it ranges from 0 N to 16000 N. Some forces due to friction are also generated during the motion.
• The graphs between Rocker Arm and Valve show the contact force between them. There are two types of plots generated for contact forces between Rocker Arm and Valve, first one is representing the net contact force generated and the second is representing contact force only in the x-direction. Graphs are plot for the cases, 3.5 mm cam lift and 6 mm cam lift.
• The difference between the two graphs is that one shows the net contact force generated between Rocker Arm and Valve and the other shows the friction force generated between them. Second graph i.e. contact force in x-direction shows the frictional force between the bodies that arises due to the Rocker Arm sliding over the surface of Valve head. The change in direction of the force is because the Rocker Arm first slides in downwards direction giving a positive friction force and then slides in upwards direction giving a negative friction force.
• The graph of linear displacement of Valve shows the motion of the valve. It is generated for the cases, 3.5 mm cam lift and 6 mm cam lift. The linear displacement of valve for 3.5 mm cam lift is 52.90 mm and for 6 mm cam lift it is 55.90 mm.

DRIVE: Files - Valve Train Assembly