MBD Simulation on IC Engine Valve Train

AIM:

To model the parts of a valve train, assemble them and run the simulation using the below parameters:

THEORY:

Valves are mechanical control elements needed to admit fresh charge and allow the burnt gases to escape out of the cylinder. Two valves, an inlet and an exhaust, are used for this purpose. Fresh mixture of fuel and air enters the inlet valve through the inlet manifold, and burnt gases pass the exhaust valve to go to the exhaust manifold.

The following types of valves are generally used on automobiles.

1. Poppet valve or Mushroom valve such as in Ambassador Diesel Nova.

2. Sleeve valve.

3. Rotary valve such as in KB125 motorcycle, Bajaj three-wheeler etc.

4. Cooled hollow valve such as a sodium cooled valve used in Alfa Romea 2000 spider veloce car.

5. Tulip Valve such as used on racing cars.

Types of Valves:

Valve Operating Mechanisms:

1. Valve Mechanism for overhead valve, under head cam shaft engine: The cam on the cam shaft lifts the tappet during its rotation. The tappet actuates the push rod which in turn operates the rocker arm about its fulcrum. The rocker arm exerts pressure on the valve stem against the spring to move the valve stem in the guide. In doing so the valve comes down from the valve seat and makes space for fuel air mixture to enter the cylinder. With more rotation of the cam shaft, the valve spring pushes back the valve on its seat when non-eccentric portion of the cam comes in contact with the tappet. Now the valve is closed.

2. Valve mechanism for overhead cam shaft engine: Some overhead valve engines are provided with an overhead cam shaft instead of underhead cam shaft. Cars like Daimler Benz, Ford Escort, Lancer, Opel Astra are provided with such valve operating mechanisms. The overhead cam shaft arrangement has high volumetric effiency and high compression ratio. But its use requires higher initial cost and complicated combustion chamber.

3. Valve mechanism for side valve engines: Such arrangements are employed on L-Head engines. The advantages and disadvantages are as follows:

Advantages:

1. Low engine height is possible as there are no parts above the cylinder head.

2. Lubrication is easier for the valve mechanism.

3. Working is quieter as there is there is no rocker arm assembly.

4. Mechanism is less complicated than that in overhead valve engine.

Disadvantages:

1. Volumetric Effiency and Compression Ratio are poor.

2. Shape of the combustion chamber is complicated.

3. Space for inlet valve is restricted.

Cam Lift:

Case 1: Cam Lift= 3.5mm

3.5 = (L- 17.5) + 10

L= 11mm

Case 2: Cam Lift= 6mm

6= (L-17.5) + 10

L= 13.5mm

GEOMETRIC SETUP:

Cam:

1) Open Solidworks. Create a new part model. Select the Front Plane and sketch.

2) Sketch as shown below, the center distance being 11mm in case 1 and 13.5mm in case 2.

Sketch for Case 1

Sketch for Case 2

3) Exit sketch. Extrude by 10mm from Midplane.

Cam in Case 1

Cam in Case 2

Push Rod:

1) Open a new part model. Select the Front Plane and sketch as shown below.

2)Exit Sketch. Use Revolved Boss/Base option using vertical line from origin as axis.

ROCKER ARM:

1) Open a new part model. Select the front plane and sketch as shown below:

2) Exit Sketch. Extrude the sketch from Mid-Plane by 20mm.

Valve:

1) Open a new part model. Select the Front Plane and draw the sketch as shown below:

2)Exit Sketch. Use Revolved Boss/Base and use vertical line from origin as axis.

Valve Mount:

1) Open a new part model. Select the Front Plane and draw the sketch as shown below. Then, draw a vertical construction line from origin.

2) Exit sketch. Use Revolved Boss/Base option using construction line as axis.

ASSEMBLY:

1) Open a new assembly model. Insert the cam first. Right click on the cam and select Float option. Click on the view temporary axis option.

2) Insert all other parts.

3) Coincide the centre axis of the rocker arm and the Right Plane of the assembly. Then coincide its centre axis with the Top Plane of the assembly. Finally coincide its Front Plane with the Front Plane of the assembly.

4) Coincide the Front Plane of the Cam with the Front Plane of the assembly.

5) Coincide the centre axis of the Push Rod with the Front Plane of the assembly.

6) Coincide the centre axis of the Valve with the Front Plane of the assembly.

7) Coincide the centre axis of the Valve Mount with the Front Plane of the assembly.

8) Drag out the Push Rod and make the perpendicular distance between it and the Right Plane of the assembly 20mm. It should be to the left of the Right Plane.

9) Drag out the Cam and make the perpendicular distance between it and the Right Plane of the assembly also 20mm. It should be to the left of the Right Plane.

10) Drag out the Valve mount and make the perpendicular distance between it and the Right Plane of the assembly 50mm. It should be to the right of the Right Plane.

11) Select the top face of the Valve Mount and make the perpendicular distance between it and the Top Plane of the assembly 60mm. Then Coincide the centre axis of the Valve and the Valve Mount. Move the valve in such a way that it fits into the valve mount.

12) Arrange the mechanism in such a way that push rod is above cam, rocker arm is above push rod, valve is below rocker arm(other side).

13) Set the Perpendicular distance between the Top Plane of Assembly and the central axis of cam as 130mm.

14) Again move the parts such that no part is meshing with another.

15) Click on the Move Contacts option. Select Physical Dynamics. Move the parts such that they just touch each other.

Assembly: Case 1

Assembly: Case 2

MOTION ANALYSIS:

1) Select Solidworks Add-Ins option. Then go to Motion Study-1. Change type of motion study to Motion Analysis.

2) Select Motor option. Under Reference axis, select central axis of Cam. Under speed, enter 1500 rpm.

3) Select Contacts option. Make contact pairs between Cam and Push Rod, Push Rod and Rocker Arm and Rocker Arm and Valve. For all the pairs, both materials will be Steel(Dry).

4) Select the spring option. Under reference edges, select the bottom edge of the tip of the valve and the top edge of the valve mount. Make Spring Constant 12N/mm and Free Length as 50mm.

5) Select all the parts, right click and select Material---->Edit Material option. In the Material Dialogue Box, search for Cast Carbon Steel and click Apply.

6) Select the Settings option. Make frame speed as 7200 fps and use precise contact.

7) Reduce end time to 0.2s and click Calculate.

8) After calculation is done Plot Results for Variation of Valve Lift, contact force between Cam and Push Rod, Push Rod and Rocker Arm and Rocker arm and Valve.

RESULTS:

Case 1: Cam Lift 3.5mm

Variation of Valve Lift:

Variation of Contact Force between Cam and Push Rod:

Variation of Contact Force between Push Rod and Rocker Arm:

Variation of X component of Contact Force between Rocker Arm and Valve:

Variation of Y component of Contact Force between Rocker Arm and Valve:

Variation of Z component of Contact Force between Rocker Arm and Valve:

Variation of Contact Force(Magnitude) between Rocker Arm and Valve:

Video Link: https://www.youtube.com/watch?v=ILsqyj4SMZI&feature=youtu.be

Case 2: Cam Lift 6mm

Variation of Valve Lift:

Variation of Contact Force between Cam and Push Rod:

Variation of Contact Force between Push Rod and Rocker Arm:

Variation of X component of Contact Force between Rocker Arm and Valve:

Variation of Y component of Contact Force between Rocker Arm and Valve:

Variation of Z component of Contact Force between Rocker Arm and Valve:

Variation of Contact Force(Magnitude) between Rocker Arm and Valve:

Video Link: https://www.youtube.com/watch?v=eYfrBjtYpY4&feature=youtu.be

INFERENCES:

Case 1:

1) Valve Lift: Peak value 52.3mm and minimum value is 50.2mm.

2) Contact Force Between Cam and Push Rod: Maximum value is 2872N.

3) Contact Force Between Push Rod and Rocker Arm: Maximum Value is 2902N.

4) Contact Force Between Rocker Arm and Valve: X-Component- Maximum Value 77N. Minimum -244N. Magnitude- Maximum Value 1006N.

Case 2:

1) Valve Lift: Peak value 54mm and minimum value is 50mm.

2) Contact Force Between Cam and Push Rod: Maximum value is 3480N.

3) Contact Force Between Push Rod and Rocker Arm: Maximum Value is 3661N.

4) Contact Force Between Rocker Arm and Valve: X-Component-Maximum Value 180N. Minimum -87N. Magnitude- Maximum Value 746N.

The Contact Force between Rocker Arm and Valve can be divided into two mutually perpendicular components- X and Y. The resultant of the two components gives the total magnitude of the contact force. Hence the plot of x component and magnitude varies.

SOURCES OF ERROR:

1) The angle between Top Plane of Assembly and Top Plane of Rocker Arm may not be 0deg.

REFERENCES:

1) Automotive Engine Parts, Automobile Engineering, MME 2204, Department of Mechanical and Manufacturing Engineering, Manipal Institute of Technology.