Motion Analysis of IC Engine Valve Train Assembly

Mohit Sachdeva
Jul 10, 2020
10 min read

Aim:- To Study Motion Analysis of IC Engine Valve Train Assembly using Solidworks

Objective:-

Model the parts and assemble them in SolidWorks.
Run the simulation at speed of 1500 RPM for 3.5 mm and 5 mm cam lift and Cast Carbon Steel material is to be used.

3. Obtain the following plots:

Valve Lift
The contact force between Cam and Push Rod
The contact force between Pushrod and Rocker Arm
The contact force between Rocker Arm and Valve

4. 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.

Introduction:-

A valve train or valve train is a mechanical system that controls the 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.

Cast Carbon Steel Properties:

Elastic Modulus = 2e+11 N/m^2

Poisson's Ratio = 0.32 N/A

Shear Modulus = 7.6e+10 N/m^2

Mass Density = 7800 kg/m^3

Tensile Strength = 482549000 N/m^2

Yield Strength = 248168000 N/m^2

Thermal Expansion Coefficient = 1.2e-05 /K

Thermal Conductivity = 30 W/(m·K)

Specific Heat = 500 J/(kg·K)

For case 1, D1=15 mm, D2=7 mm, therefore L=7.5 mm

Cam lift = (L-R1)+R2 = (7.5-7.5)+3.5 = 3.5 mm , here L is measured in 3D model

OR L can be calculated using this formula

cam lift=3.5 mm, R1=7.5 mm, R2=3.5 mm

Therefore, 3.5=(L-7.5)+3.5

L=7.5 mm

Similarly,

For case 2, D1=25 mm, D2=12 mm, therefore L=12.5 mm

Cam lift = (L-R1)+R2 = (12.5-12.5)+6 = 6 mm , here L is measured in 3D model

OR L can be calculated using this formula

cam lift=6 mm, R1=12.5 mm, R2=6 mm

Therefore, 3.5=(L-12.5)+6

L=12.5 mm

3D Models :-

Cam:

A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion. It is often a part of a rotating wheel (e.g. an eccentric wheel) or shaft (e.g. a cylinder with an irregular shape) that strikes a lever at one or more points on its circular path.

The timing and lift profile of the valve opening events are controlled by the camshaft, through the use of a carefully shaped lobe on a rotating shaft. The camshaft is driven by the crankshaft and— in the case of a four-stroke engine— rotates at half the speed of the crankshaft. Motion is transferred from the crankshaft to the camshaft most commonly by a rubber timing belt, a metallic timing chain, 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 (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.

Valve:

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.

Valve Mount:

This is used to guide the translatory motion of the valve and also to support the spring.

Assembly:-

Motion Analysis:-

Study 1- Cam lift of 3.5 mm rotating at 1500RPM clockwise and the material of all components being Cast Carbon Steel

For case 1, D1=15 mm, D2=7 mm, therefore L=7.5 mm

Cam lift = (L-R1)+R2 = (7.5-7.5)+3.5 = 3.5 mm

The material of components - Cast Carbon Steel

Linear valve spring of stiffness = 10 N/mm and length = 45 mm is used.

The motor of 1500RPM in a clockwise direction for camshaft is used.

7200 FPS with precise contacts in selected for smooth motion simulation so that precise values can be obtained for every cam angle of rotation.

Plots/Graphs:-

1. Valve Lift

As the cam starts touching the pushrod, the force is transferred to the valve by the rocker arm. The force just acts before 0.25 seconds, which gradually increases due to the cam profile. The peak represents that the valve is fully pushed down by the rocker arm because the position of the cam is such that it fully extends the pushrod as per the cam lift. As the peak gradually decreases, the force gradually reduces and the valve returns to its initial position due to the force acting by the valve spring. There are some little variations when the cam is idle(not in contact with pushrod) due to the friction in the mechanism.

The maximum value of valve lift = 53.49 mm whereas minimum value = 50.50 mm.

Therefore, valve lift = 2.99 mm, for a cam lift of 3.5 mm

2. The contact force between Cam and Push Rod

The sharp peaks in the graph represent the sudden force applied by the cam to the pushrod due to the rotation of the cam at 1500 RPM in the clockwise direction. Whereas, the small ripples denotes the friction between the cam and the pushrod. The peaks are quite sharp because the cam is rotating at a very high speed, but it can be similar to the previous graph if the rotation is slow and thus it will clearly represent the gradual rise and fall of the force acting on the pushrod as per the cam profile.

The maximum contact force between Cam and Push Rod = 13231 N whereas minimum force = 0 N

3. The contact force between Pushrod and Rocker Arm

The sharp peaks in the graph represent the sudden force applied by the pushrod to the rocker arm due to the force applied on the pushrod by the rotation of the cam at 1500 RPM in the clockwise direction. Whereas, the small ripples denotes the friction between the pushrod and the rocker arm. The peaks are quite sharp within a minute time period because the cam is rotating at a very high speed, but if the rotation is slow it will clearly represent the gradual rise and fall of the force acting on the pushrod as per the cam profile. The maximum contact force between the cam and the pushrod is 13231 N whereas the maximum contact force between the cam and the pushrod is 13094 N, there is a small decrease in the force due to the friction in the mechanism which can be improved by modifying the design.

The maximum contact force between Pushrod and Rocker Arm = 13094 N whereas minimum force = 0 N

4. The contact force between Rocker Arm and Valve

The sharp peaks in the graph represent the sudden force applied by the rocker arm to the valve by the translatory motion of the pushrod. Whereas, the small ripples denotes the friction between the parts. The peaks are quite sharp within a quick time period because the cam is rotating at very high speed (1500 RPM). Here the maximum contact force is 2461 N which is very less than the maximum contact force between the pushrod and the rocker arm (13094 N) because, at this stage, the translatory force by the pushrod is transferred to the rocker arm in a rotary motion as the rocker arm is fixed at the pivot and this force is again transferred to the valve in the form of translatory motion of the valve. Moreover, some amount of force is lost by the friction present between the mechanism.

The maximum contact force between Rocker Arm and Valve is 2461 N and the minimum force = 26.17 N

5. The contact force between Rocker Arm and Valve in X-direction

In this graph, the reaction force is negative because it is applied in the downward direction by the rocker arm on the valve. The horizontal ripples show sliding friction of rocker arm on the valve and the sudden drop in the graph shows the vertical frictional force applied by the rocker arm on the valve. There is a vast visible difference in the graphs of contact force between the rocker arm and the valve as magnitude and in X-direction. The magnitude graph simply represents the overall force acting on the valve whereas the X-direction graph represents the contact force just acting in the X-axis.

Study 2- Cam lift of 6 mm rotating at 1500RPM clockwise and the material of all components being Cast Carbon Steel

For case 2, D1=25 mm, D2=12 mm, therefore L=12.5 mm

Cam lift = (L-R1)+R2 = (12.5-12.5)+6 = 6 mm

The material of components - Cast Carbon Steel

Linear valve spring of stiffness = 10 N/mm and length = 45 mm is used.

The motor of 1500RPM in a clockwise direction for camshaft is used.

7200 FPS with precise contacts in selected for smooth motion simulation so that precise values can be obtained for every cam angle of rotation.

Plots/Graphs:-

1. Valve Lift

As the cam starts touching the pushrod, the force is transferred to the valve by the rocker arm. The force just acts around 0.225 seconds, which gradually increases due to the cam profile. The peak represents that the valve is fully pushed down(open) by the rocker arm because the position of the cam is such that it fully extends the pushrod as per the cam lift. As the peak gradually decreases, the force gradually reduces and the valve returns to its initial position due to the force acting by the valve spring and simultaneous reduction of the force by the cam. There are some little variations when the cam is idle(not in contact with pushrod) due to the friction in the mechanism. Comparing this graph with similar to the study1, it is quite clear that the valve lift is directly proportional to the cam lift for this type of assembly.

The maximum value of valve lift = 59.77 mm whereas minimum value = 50.48 mm.

Therefore, valve lift = 9.29 mm, for a cam lift of 6 mm

2. The contact force between Cam and Push Rod

If we compare this graph with the similar plot of study 1 that is for the cam lift of 3.5 mm, we observed that the maximum force is approximately double that of study 1.

The maximum contact force between Cam and Push Rod = 25369 N whereas minimum force = 0 N

3. The contact force between Pushrod and Rocker Arm

The sharp peaks in the graph represent the sudden force applied by the pushrod to the rocker arm due to the force applied on the pushrod by the rotation of the cam at 1500 RPM in the clockwise direction. Whereas, the small ripples denotes the friction between the pushrod and the rocker arm. The peaks are quite sharp within a minute time period because the cam is rotating at a very high speed, but if the rotation is slow it will clearly represent the gradual rise and fall of the force acting on the pushrod as per the cam profile. The maximum contact force between the cam and the pushrod is 25369 N whereas the maximum contact force between the cam and the pushrod is 25079 N, there is a small decrease in the force due to the friction in the mechanism which can be improved by modifying the design.

The maximum contact force between Pushrod and Rocker Arm = 25079 N whereas minimum force = 0 N

4. The contact force between Rocker Arm and Valve

The sharp peaks in the graph represent the sudden force applied by the rocker arm to the valve by the translatory motion of the pushrod. Whereas, the small ripples denotes the friction between the parts. The peaks are quite sharp within a quick time period because the cam is rotating at very high speed (1500 RPM). Here the maximum contact force is 4752 N which is very less than the maximum contact force between the pushrod and the rocker arm (25079 N) because, at this stage, the translatory force by the pushrod is transferred to the rocker arm in a rotary motion as the rocker arm is fixed at the pivot and this force is again transferred to the valve in the form of translatory motion of the valve. Moreover, some amount of force is lost by the friction present between the mechanism.

The maximum contact force between Rocker Arm and Valve is 4752 N and the minimum force = 25.98 N

5. The contact force between Rocker Arm and Valve in X-direction

Simulation:-

Google drive link -

https://drive.google.com/drive/folders/118flXBs-IJPYY7KGfg7K4DXYJOiYjaCP?usp=sharing

Conclusion:-

By comparing both the cases, we observed that valve lift increases with an increase in cam lift. Therefore, the cam geometry affects the linear distance of valve opening and closing.
The valve lift is greater than the cam lift. For a 3.5 mm cam lift, the valve lift is 2.99 mm, and for a 6 mm cam lift, the valve lift is 9.29 mm.
The contact forces increase with an increase in cam lift which can be clearly observed from comparing both the above-studied cases.
The magnitude of contact forces between the parts is decreased as compared from the origin that is the contact force between the cam and the pushrod gets reduced when it reaches the valve through the rocker arm due to the friction in the mechanism.
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 represents the amount of force applied on the valve by the rocker arm whereas force in x_direction represents sliding friction of the rocker arm on the valve.
On comparing both the studies overall, it is clear that by increasing the cam lift, the contact force increases in the assembly due to which the valve lift also increases. Higher the cam lift, the higher the displacement of the pushrod due to which higher will be the displacement of the rocker arm; finally higher will be the displacement of the valve.

Reference:-

https://en.wikipedia.org/wiki/Valvetrain#:~:text=A%20valvetrain%20or%20valve%20train,in%20an%20internal%20combustion%20engine.

https://mgispeedware.com/camshaft-calculator/

Tags- #valvetrainsimulation #valvetrain #enginecomponents #engineparts #simulation #analysis #inference #report #valvedesign #multibodydynamics #mbd #fea #ingeniousmechanics #mechanics #productdesign #productenhancement #productimprovement #productinnovation #trending #upgrade #mechanics #mechanicalengineer #mechanicalengineering #cad #cam #cae

Motion Analysis of IC Engine Valve Train Assembly

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