IC ENGINE VALVE TRAIN

AIM

• Model the parts and assemble them in SolidWorks.

• 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 PushRod

• 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 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 of air /fuel mixture into the combustion chamber , while the exhaust valves controls the flow of spent exhaust gasses out of the combustion chamber

Theory and Explanation

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 belt , A metallic timing chain or a set of gears

Push rod

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.

Valves

Most modern engines use poppet valve 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 valve train at high engine speeds (RPM)

250 times

Valve lift

Cam lobes also plays an vital role in ic engine as we know that cam is responsible for opening and closing of valve as greater the height of lobe in cam greater the force for more valve lift which allows air in an out in an engine cylinder

As more the valve lift more we can puts air and fuel in engine

As cam lift is directly proportional to valve lift as cam lift increases is increases the valve lift

Linear displacement of valve also increases

cam lift

Valve spring

Valve springs play an important role in controlling the breathing in internal combustion engines. The valves are mechanically opened by a camshaft, via valve lifters or tappets, and closed by the valve springs.

pneumatic valve spring

This valve is mainly used in racer where the rpm is also high around 15000 rpm means the piston is 250 revolution per second that means 250 times piston are moving from top dead center to bottom dead center in an engine

Where in normal vehicles the rpm is 12000

Rpm limits can hinders due to racer car runs faster than normal vehicles

There is major reasons in this conventional spring valve have an upper operational limit 12000 rpm if engine ran any faster the spring in the valve cannot insured to valve returns to their original position along with the cam follower that lives to lot of contact between the cam follower an the cam this is called as valve float that cause a valve to wide open when piston arrives to TDC that cause collision between the valve and piston which can leads to serious mechanical damages and failure

So for high speed or rpm pneumatic valve is introduced

The construction of the pneumatic valve spring is similar to the conventional valve they have metal bellows which are filled with compressed air in the place of spring we have pneumatic bellows so when the cam pushes down on the valve the pressurised air in the bellows that compressed this pressurised air act as a spring so that valve can operate at high valueof rpm

But this valve have their limitations when air pressurised the air always find find way out especially when its pressurised 10 bar 10 bar = 10 times atmospheric pressure to prevent this the below is connected to reservoir which is as much higher pressures when itis drop in pressure inside the bellows the air from the reservoir can be used to level it .

Valve timing

In a piston engine , the valve timing is the precise timing of the opening and closing of the valves.

Objectives

To understand the basic parts of valve train and mechanism and how to model and simulate

The main objective is to avoid the over jump of the system of valve in ic engine this is purpose of the modification of the valve system to improve efficiency of ic engines

Results and plots

As the rocker arm plays vital role to force to valve to open which results in positive force as a spring exerts a backward force instantly which results in negative force due to sudden change a point of contact of valve the valve changes direction to y directions and close the valve

So along x direction contact force is shown in a plot negative and positive side

The magnitude represents net contact force between the parts or contact between rocker arm and valve as the rotation is in the x-y plane

F =`square root` fx2 +fy2

where along x component the contact force is the frictional force that arises due to sliding of rocker arm on the surface of valve

Conclusion

Cam lobe is value high more is valve lift and more we puts air and fuel in engine cylinder

The force direction changes between the rocker arm and valve along x component

Magnitude give net contact force between the parts

Pneumatic valve is give high speed or rpm