MBD Simulation on IC Engine Valve Train

MBD SIMULATION ON IC ENGINE VALVE TRAIN

AIM – Create 3D models of cam, push rod, rocker arm, valve, and valve mount and perform motion analysis using Solidworks.

OBJECTIVES-

1. Create 3D models of cam, push rod, rocker arm, valve, and valve mount.
2. Perform motion analysis by rotating cam at according to following two cases-

Sr. No.	CAM Lift (mm)	Crank speed ( rpm)	Material
1	3.5	1500	Cast Carbon Steel
2	6	1500	Cast Carbon Steel

3. Obtain the following plots
4. Valve Lift
5. Contact force between
   1. Cam and push rod
   2. Push rod and Rocker arm
   3. Rocker arm and valve

INTRODUCTION-

A valve train is a mechanical system that controls operations of valves in an internal combustion engine through movement of its components. Conventional reciprocating internal combustion engine uses valves to control flow of air/fuel mixture in and out of the engine.

Valve train opening and closing duration, its geometry is what decides the amount of air and fuel entering in engine at any time. This time factor is controlled by camshaft which is synchronized to crankshaft with chains. The camshaft is located in engine block and operates direct control of valves or indirectly via push rods and rocker arm. It is why they are sometimes called pushrod engines.

Cam Lift is the distance the cam lobe rises away from the base circle of the camshaft. It is the distance the lifter moves.

CALCULATIONS-

We know the cam lift can be calculated using formula

Cam Lift = L – R1+ R2

R1 is radius of base circle

R2 is radius of upper circle

L is distance between centres of two circles,

Now, in our simulation we have R1=12.5mm & R2=5mm.

Case 1 Cam lift = 3.5mm

So, we have 3.5 = L – 12.5 + 5

L=11 mm

Case 2 Cam list = 6mm

So, we have 6 = L – 12.5 + 5

L = 13.5 mm

So, we design our cams accordingly.

PROCEDURE-

1. Create following parts in Solidworks, using following drawings.

• Cam ( both with cam lift 3.5mm and 6mm)
• Push Rod
• Rocker arm
• Valve
• Valve mount

2. Now click on NEW> ASSEMBLY. For case 1 with let us start with cam of cam lift 3.5 mm.
3. Provide proper mates with assembly’s Front, Top and Right planes and also between temporary axes of components.
4. Now click on Move component > Physical Dynamics and move valve till collision takes place and no further motion is possible.

5. Enable Solidworks Motion from Tools > Add in. Click on Motion Study palette. Select Motion Analysis from Drop Down Menu.
6. Now select all the components of assembly, right click on Material > Edit material > Cast Carbon Steel.
7. Click on motor icon. By default, selection is Rotary Motor. Select axis of cam in component. In Motion select Constant Speed with 1500 RPM in clockwise direction.
8. Click on Contact and make following contacts: - between cam and push rod, between push rod and rocker arm and finally between rocker arm and valve.
9. Now click on spring and place it above valve mount and valve head face. Use k= 10N/m and free length as 45mm which makes spring initially compressed.
10. Click on Motion property manager and set Frame per seconds to 9000. Select use precise contact option. Now click on Calculate.
11. Plot the required displacement and contact forces.
12. For case 2 replace the cam with cam of 6mm cam lift. Repeat all the above steps.

RESULTS –

Case1 Cam Lift = 3.5 mm

Case2 Cam Lift = 6 mm

Contact force between rocker arm and valve along X direction-

EXPLANATIONS & CONCLUSIONS:

1. The magnitude represents net contact force between the parts, while contact force along the X direction is frictional force between the bodies that arise due to sliding of rocker arm surface over valve head.
2. The change in direction of frictional force is because rocker arm first slides towards origin giving a positive friction force against the motion and then slides away from the origin giving rise to friction in negative X direction.
3. When comparing the plots of case 1 and case 2, we can see that they are similar. Only the value of magnitude changes. Also, in case 2 graphs are smoother.
4. We can clearly see that valve lift is much higher in case 2 when we compare with case 1. Hence, a larger amount of air/fuel ratio can enter the engine.
5. Valve lift is less than respective cam lift in both the cases.
6. Fluctuating value of contact forces, results in vibrations in the assembly.
7. Free length of spring must be selected as such that it is compressed in initial state. The pre-compression created in spring must be enough to always maintain the contact between push rod and rocker arm.