MBD Simulation on IC Engine Valve Train

Aim : Model the parts of IC Engine Valve Train and assemble them in SolidWorks. 

         And Run the simulation using the below parameters

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

 Obtain the

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

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 valvetrain or 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 (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 combusion chamber once combustion is completed.

Let’s Talk about different parts and their respective solidworks 3D Model.

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 or shaft that strikes a lever at one or more points on its circular path.

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 float occurs when the valve spring is unable to control the inertia of the valvetrain at high engine speeds (RPM).

Valve seat: The valve seat in an internal combustion gasoline or diesel engine is the surface against which an intake or an exhaust valve rests during the portion of the engine operating cycle when that valve is closed. The valve seat is a critical component of an engine in that if it is improperly positioned, oriented, or formed during manufacture, valve leakage will occur which will adversely affect the engine compression ratio and therefore the engine efficiency, performance (engine power and engine torque), exhaust emissions, and engine life.

Basic theory on the motion study:

motion study as the “Science of eliminating wastefulness resulting from ill-directed and inefficient motions”. The main aim of motion study is to find the scheme of least wastage of labour. Subsequently, the scope of Motion Study was enlarged and it was named as Method Study.

Ready your every parts and assemble them.

Entire Motion Analysis Setup:

Switching to SolidWorks Motion Manager Switch to SolidWorks Motion by clicking the motion analysis tab in the bottom left hand corner.

SolidWorks Assembly Mates.

Specifying the Input Motion and

Under Motor Type selet Rotary Motor. In our case i have used 1500 rpm constant motor at Cam

Select contact between parts. Between cam and pushrod,pushrod and Rocker arm,Rocker Arm and Valve.

Select material as Cast carbon steel:

Go to settings and set frames per seconds as per our requirements. I have used 9000 as per calculation.

Put a spring between the faces of Valve and valve seat as follows:

Select Simulation time.i have choosen 0.2 sec

Running the Simulation.

Looking at the Results. And select plots as per our requirements.

Let’s go through one by one,

Model Description :

Motion analysis for two different cases as follows:

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

 Cam lift formula :

Case 1: Motion Analysis for cam lift of 3.5mm:

To calculate the distance between the two centres(L)

Given:

 R1 = 12.5;

R2 = 5;

Cam lift = 3.5mm

Cam lift = (L-R1)+R2

L = (12.5+3.5) - 5

L = 11mm

Here is the cam dimensions :

Assembly for case 1:

Results : 

Valve lift:

Contact force between Cam and Pushrod :

Contact force between Pushrod and Rocker arm:

Contact force between Rocker arm and valve (magnitude):

Contact force between Rocker arm and valve (In X-direction):

Animation link for case 1: https://youtu.be/96QCacafsgE

Case 2: Motion Analysis for cam lift of 6mm:

To calculate the distance between the two centres(L)

Given:

R1 = 12.5;

R2 = 5;

Cam lift = 3.5mm

Cam lift = (L-R1)+R2

L = (12.5+6) - 5

L = 13.5mm

Here is the cam dimensions :

Assembly for case 2:

Results : 

Valve lift:

Contact force between Cam and Pushrod :

Contact force between Pushrod and Rocker arm:

Contact force between Rocker arm and valve (magnitude):

Contact force between Rocker arm and valve (In X-direction):

Animation link for case 2:  https://youtu.be/jq-qxsN3INI

Observation And Conclusion :

• The contact forces between each component and linear displacement of the valve for the cam lift of 6mm is ‘larger than’ the cam lift of 3.5mm. This shows that CAM geometry affects the amount of opening of the valve through which the mixture enters the cylinder.
• The linear displacement of the valve is greater than the lift produced by the CAM as the Rocker arm towards the valve is greater than that towards the pushrod.
• In the plot of contact forces against time for rocking arm and the valve, a minimum force is always present due to the initial compressed state of the spring.
• The contact forces are at their peaks when the CAM lobe is at its topmost position.
• The Magnitude represents net contact force between the parts, while the contact force along the X direction is the frictional force between the bodies that arise due to the rocker arm sliding over the surface of the valve head.
• The change in direction of the force is because the rocker arm first slides towards origin giving a positive friction force (opposing the motion) and then slides away from the origin giving rise to friction in the negative x-direction. Therefore the plots are opposite to each other.
• The explanation is same for the cam lift of 6 mm, only it differs in magnitude of contact forces. The movement in this case is quite smoother compared to the cam lift of 3.5 mm as observed. As the cam lift increases more air-fuel mixture can enter into the cylinder of IC engine.