MBD Simulation on IC Engine Valve Train

AIM:

Simulation on IC Engine Valve Train

OBJECTIVES OF THE PROJECT:

Run the simulation using the below parameters

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

INTRODUCTION:

Valvetrain

A 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 into the combustion chamber, while the exhaust valves control the flow of spent exhaust gasses out of the combustion chamber once combustion is completed.

Components:

The valvetrain consists of all the components responsible for transferring the rotational movement of the camshaft into the opening and closing of the intake and exhaust valves. Typical components are listed below in order from the crankshaft to the valves.

CamShaft: -

The timing and lift profile of the valve opening events are controlled by the camshaft, through 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: -

Works as an intermediate between camshaft and the valves. Camshaft pushes up the rocker arm (via push rod) which in turns pushes down on the vales.

Valves: -

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).

The overall assmebly of these components is shown below:

BODY OF THE CONTENT:

All the parts which are being constructed are shown below,

Cam

Pushrod

Rocker Arm

Valve

Valve Mount

Important part being the CAM which will decide the lift, for constructing the desired lift let us look at the given formula: -

`C=(L-R_1 )+R_2`....(1)

Where C is the cam lift,

L be the centre distance between two circles.

R₁ and R₂ are the radius of lower and upper circles respectively.

For the convenience Let us take the Lower circle Diameter be 25cm in both the cases and whatever will be the upper radius must be coincide with the radius of the lower circle.

In such a condition the lower radius R₁ and the centre distance between both the circle will become equal.

Such that

`R_1=L`...(2)

From 1^st and 2^nd equation,

`C=R_2`....(3)

From equation 3^rd it can be seen that cam lift will only depend upon the radius of the upper circle.

So, for the sketches would be something like shown below:

For 6mm lift for 3.5 mm lift

Now just assmebling all the components with fundamental mates.

Now simulating the Two cases let us take the case of

1) 6mm cam lift:

Material: Plain Carbon Steel

RPM: 1500

Spring Stiffness(N/mm): 10

the Plots which are required are shown below:-

from the Above graph it is clearly seen that the displacement is more than 6mm which is due to the less spring stiffness which results in pushing the Push_rod more than desired.

Conatact Froces:

Both above Figures are contact force between rocker arm and pushrod 2nd one is in the x-dircetion.

From the above contact forces diagram it could be seen that at certain point the forces gets a maginfied due to the fact that as the spring stiffness is quite low which results in rasing the push_rod a bit higher dueto which when it moves down thier is an sudden impact on to the cam.

To avoid these two factors of sudden impact let us increase the spring stfiness a bit higher

2) 3.5mm cam lift:

Material: Plain Carbon Steel

RPM: 1500

Spring Stiffness(N/mm): 15

the Plots which are required are shown below:-

Due to the increase in the spring stiffness it could be seen that the lift is more asccurate as required

Conatact Froces:

Both above Figures are contact force between rocker arm and pushrod 2nd one is in the x-dircetion.

from all the above diagrams of contact forces it could be seen that with the increase in the spring stiffness the range of the forces are narrowed as well as thier is not much impact force on to the cam.

CONCLUSION:

• The linear displacement of the valve is greater than the lift produced by the CAM as the moment arm towards the valve is greater than that towards the pushrod.
• 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.
• Contact force between the Rocker arm and valve varies while measuring with respect to the X-direction and measuring with respect to magnitude because if we look at the plot of the X – component of the contact against time, it achieves negative force because the rocker arm slides both forwards and backward during one complete rotation of the CAM and hence the friction force acts in both direction. The magnitude of the contact force between the rocker arm and the valve pushes the valve downwards, but its X- component gives us only the friction force of the rocker arm sliding over the face of the valve head.
• The files to run the simulation is in the given below link

https://drive.google.com/drive/folders/14pyQytJpEZdSR84_QNzsx1x6LIk6d7Om?usp=sharing

• (NOTE: For running the simultaion for both cases(one after another), just replace the Cam component and apply the constraints, calculate the motion analysis again)

The simulation of above two cases is shown below: