MBD Simulation on IC Engine Valve Train

Aim:

• To create all the parts required for IC Engine Valve Train assembly with the 2 following cases:
  

  S.No.	CAM lift (mm)	Speed (RPM)	Material
  1.	3.5	1500	Cast Carbon Steel
  2.	5	1500	Cast Carbon Steel

• To plot the following graphs in both the cases:
  i. Valve Lift.
  ii. The contact force between :

• Cam and Push Rod
• Pushrod and Rocker Arm
• Rocker Arm and Valve
  
• Also, 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:

Valve Trains:
A valve train is a mechanical system that controls operation of the intake and exhaust valves in an internal combustion engine.

Components of IC Engne Valve Train Assembly:

1. Cam
2. Push Rod
3. Rocker Arm
4. Valve Mount/Valve Guide
5. Valve

For better understanding an schematic figure is given below:

* Cam:
A rotating or sliding piece (such as an eccentric wheel or a cylinder with an irregular shape) in a mechanical linkage used especially in transforming rotary motion into linear motion or vice versa.

* Push Rod:
A metal rod transmitting the reciprocating motion that operates the valves of an internal-combustion engine having the camshaft in the crankcase.

* Rocker Arm:
A rocker arm is an oscillating lever that conveys radial movement from the cam lobe into linear movement at the poppet valve to open it.

* Valve Mount/Valve Guide:
A valve guide is a cylindrical piece of metal, pressed or integrally cast into the cylinder head, with the valve reciprocating inside it.

* Valve:
A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways.

Formula:

Cam Lift:
It is the distance which the lifter moves to.

Procedure:

1. Model Design:
Includes making the cad model of the system that is to be analyzed.

2. Assembly:
With the help of mates parts are combined to form an Assembly.

3. Applying Set-Up:
Includes setting up the motor, contacts and material.

4. Motion Analysis:
The solver is run giving out the results for plots including forces,velocities,accelerations and identifying the minimum and maximum values of those to determine the critical regions.

Case Study:
1. Model Design:
First,we start with the modelling of cam.

* Cam:
Since there are two conditions given we have to model 2 Cams.

Calculation of distance between the centre of circles:

i. Case 1:
We have, Cam lift = 3.5 mm ; Major Circle Radius (R1) = 12.5 mm ; Minor Circle Radius(R2) = 5 mm

Using the formula,

Cam lift = (L − R1) + R2

3.5 = (L − 12.5) + 5

L = 11

The complete model is shown below:

Fig 1: 3D Model of Cam-Case 1

ii. Case 2:

We have, Cam lift = 3.5 mm ; Major Circle Radius (R1) = 12.5 mm ; Minor Circle Radius(R2) = 5 mm

Using the formula,

Cam lift = (L − R1) + R2

6 = (L − 12.5) + 5

L = 13.5

The complete model is shown below:

Fig 2: 3D Model of Cam-Case 2

* Push Rod:

Next we model the push rod. Given below is the push rod model:

Fig 3: 3D Model of Push Rod

*

Rocker Arm:

Now we start with the modelling of Rocker arm. Given below is the Rocker Arm model:

Fig 4: 3D Model of Rocker Arm

* Valve Mount:

Now we start with the modelling of Valve Mount. Given below is the Valve Mount model:

Fig 5: 3D Model of Valve Mount

* Valve:

Lastly, we start with the modelling of Valve. Given below is the Valve model:

Fig 6: 3D Model of Valve

2. Assembly:

Since there are two cases given,there are two assemblies to be made. We will start off with inserting all the part models in Assembly section and then apply essential mates to them for making an complete IC Engine Valve Train Assembly.

i. Case 1: Cam Lift = 3.5 mm

Given below is the completed assembly of the first case:

Fig 7: IC Engine Valve Train Assembly for Cam Lift of 3.5 mm

ii. Case 2: Cam Lift = 6 mm

Given below is the completed assembly of the second case:

Fig 8: IC Engine Valve Train Assembly for Cam Lift of 6 mm

3. Applying Set-Up:

• In Motor, select Constant Speed and enter 1500 RPM.
  
  
  
• In Motion Study Properties, enter 9000 FPS(to see each stroke precisely) and enable Precise Contact.
  
  
• Establish contacts between Cam & Push Rod; Push Rod & Rocker Arm; Rocker Arm & Valve.
  
  
• In Spring options, select Linear Spring with Spring Stiffness as 10 N/mm and free length of 45 mm.

Given below is an representation of the Assembly with Spring:

Fig 9: Spring Applied

Below shown are the set-ups applied to this study:


Fig 10: Applied Set-Up

4. Motion Analysis:

Once the analysis is done the below given results are obtained for the Linear Displacement & Contact Forces plots.

i. Case 1:

* Linear Displacement Plot of Valve :

Fig 11: Linear Displacement Plot of Valve

Fig 12: Linear Displacement Plot of Valve in Excel

* Contact Forces Plot Between Cam & Push Rod:


Fig 13: Contact Forces Plot Between Cam & Push Rod

Fig 14: Contact Forces Plot Between Cam & Push Rod in Excel

* Contact Forces Plot Between Rocker Arm & Push Rod:

Fig 15: Contact Forces Plot Between Rocker Arm & Push Rod

Fig 16: Contact Forces Plot Between Rocker Arm & Push Rod in Excel

* Contact Forces Plot Between Rocker Arm & Valve:

Fig 17: Contact Forces Plot Between Rocker Arm & Valve(Magnitude)

Fig 18: Contact Forces Plot Between Rocker Arm & Valve(Magnitude) in Excel

ii. Case 2:

* Linear Displacement Plot of Valve:

Fig 19: Linear Displacement Plot of Valve

Fig 20: Linear Displacement Plot of Valve in Excel

* Contact Forces Plot Between Cam & Push Rod:

Fig 21: Contact Forces Plot Between Cam & Push Rod

Fig 22: Contact Forces Plot Between Cam & Push Rod in Excel

* Contact Forces Plot Between Rocker Arm & Push Rod:

Fig 23: Contact Forces Plot Between Rocker Arm & Push Rod

Fig 24: Contact Forces Plot Between Rocker Arm & Push Rod in Excel

* Contact Forces Plot Between Rocker Arm & Valve:

Fig 25: Contact Forces Plot Between Rocker Arm & Valve(Magnitude)

Fig 26: Contact Forces Plot Between Rocker Arm & Valve(Magnitude) in Excel

Observation:

• Case 1:
  i. Contact Forces Plot Between Rocker Arm & Valve(Magnitude):
  

Fig 27: Contact Forces Plot Between Rocker Arm & Valve(Magnitude)

Fig 28: Contact Forces Plot Between Rocker Arm & Valve(Magnitude) in Excel

ii. Contact Forces Plot Between Rocker Arm & Valve(X-Direction):

Fig 29: Contact Forces Plot Between Rocker Arm & Valve(X-Direction)

Fig 30: Contact Forces Plot Between Rocker Arm & Valve(X-Direction) in Excel

• Case 2:
  i. Contact Forces Plot Between Rocker Arm & Valve(Magnitude):

Fig 31: Contact Forces Plot Between Rocker Arm & Valve(Magnitude)

Fig 32: Contact Forces Plot Between Rocker Arm & Valve(Magnitude) in Excel

ii. Contact Forces Plot Between Rocker Arm & Valve(X-Direction):

Fig 33: Contact Forces Plot Between Rocker Arm & Valve(X-Direction)

Fig 34: Contact Forces Plot Between Rocker Arm & Valve(X-Direction) in Excel

Parts and Plots:

To get all the parts, assembly and graphs access the below given link:
https://drive.google.com/file/d/1otgBhHyRcJ_-vDUJzswdR38h5-seGOfA/view?usp=sharing

Conclusion:

• The maximum valve lift during motion obtained from plot is 55.48 mm while minimum one is observed to be 50.343 mm. Hence, valve lift can be calculated as the difference between these two positions which comes out to be 5.137 mm.
• From the plot of contact force between cam and pushrod, initially the force was too high, it was due to sudden contact of the parts and jerk of the system. After this the force varies with gradual ups and downs with a maximum value around 17306 N.
• Similarly from the plots of contact force between rocker arm and pushrod, and contact force between rocker arm and valve, initially the force was too high and was due to sudden contact and jerk of the system. After this the force varies with gradual ups and downs with a maximum value around 17413 N and 3269.9 N respectively.
• 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 line of action of the contact forces keeps changing continuously and along X direction the surfaces of valve and rocker arm rubs over each other and produces friction between them and is both positive and negative as obtained from the plots. This frictional force tends to increase losses in energy and will dissipate as heat. On the other hand, the contact force magnitude calculates vector sum of forces in all three directions and will be greater than forces in either directions.
• Free length of spring should be carefully selected to maintain precompression in the spring.As is it fails to maintain the precompression it would not be able to allow tha motoin in the Assembly,thus making the mechanism useless without any output.