MBD Simulation on IC Engine Valve Train

AIM :– MBD simulation on IC Engine valve train

ABSTRACT :- In this project we will model the IC engine valve train with cam- lift of 3.5mm and 6mm and study its effect on the valve lift & the forces between different contacting surfaces.

INTRDUCTION :- The valve train of an internal combustion engine includes components required to control the flow of gases into and out of the combustion chamber. This includes valves and related components required to allow the air-fuel mixture to enter the combustion chamber, seal the combustion chamber during compression and combustion, and evacuate exhaust gases when combustion is complete.

Valve train Components –

1.) Rocker Arm - Rocker Arms are typically in between the pushrod and the intake and exhaust valves. Itisresponsible for translating the profile of the camshaft into motion for opening and closing the intake and exhaust valves.

2.) Cam - Camshaft, in internal-combustion engines, is a rotating shaft with attached disks of irregular shape (the cams), which actuate the intake and exhaust valves of the cylinders. The cams and the camshaft are usually formed as a unit, with the cams set at angles so as to open and close the valves in a prescribed sequence as the cams rotate.

3.) Push Rod - A metallic rod actuated by a cam to push the rocker arm which in turn open or close a valve of an internal combustion engine.

4.) Valve - Engine Valves are mechanical components used in internal combustion engines to allow or restrict the flow of fluid or gas to and from the combustion chambers or cylinders during engine operation. Functionally, they perform similarly to many other types of valves in that they block or pass flow, however, they are a purely mechanical device that interfaces with other engine components such as rocker arms in order to open and close in the correct sequence and with the correct timing.

5.) Valve Mount - The valve mount 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.

Valve_Train_assembly –

Working –

The valve which allows mixture into the cylinder is the inlet valve; the one through which the spent gases escape is the exhaust valve. They are designed to open and close at precise moments, to allow the engine to run efficiently at all speeds.

The operation is controlled by pear-shaped lobes, called cams, on a rotating shaft, the camshaft , driven by a chain, a belt, or a set of gears from the crankshaft .

Where the camshaft is mounted in the engine block , small metal cylinders tappets sit in channels above each cam, and from the tappets metal pushrod extend up into the cylinder head . The top of each pushrod meets a rocker arm which bears against the stem of a valve, which is held in a raised (closed) position by a strong coiled spring the valve spring .

As the pushrod rises on the cam it pivots the rocker arm, which pushes the valve down (open) against the pressure of its spring. As the cam lobe rotates further, the valve spring acts to close the valve.

INPUT PARAMETERS :-

Cam Modelling –

a.) Case I:- For cam-lift of 3.5 mm

b.) Case II:- For Cam-lift of 6 mm

Material (Cast Carbon Steel) Properties -

CAST CARBON STEEL PROPERTIES
	S.No.	Property	Values	Unit
	1	Elastic Modulus	2.00E+11	N/m^2
	2	Poisson's Ratio	0.32	N/A
	3	Shear Modulus	7.60E+10	N/m^2
	4	Mass Density	7800	kg/m^3
	5	Tensile Strength	4.83E+08	N/m^2
	6	Compressive Strength		N/m^2
	7	Yield Strength	2.48E+08	N/m^2
	8	Thermal Expansion Coefficient	1.20E-05	/K
	9	Thermal Conductivity	30	W/(m·K)
	10	Specific Heat	500	J/(kg·K)
	11	Material Damping Ratio		N/A

PROCEDURE :-

• Create all parts of valve train in solidworks part modelling.
• Create 2 Cam profiles for camlift of 3.5 mm and 6 mm.
• Assemble all components of valve train in solidworks assembly by making required mates.
• After assembly, select all componrnts and assign material as Cast Carbon Steel. It will be reflected in assembly by change in color of parts.
• Make proper contacts between the components by using move component command with physical dynamics option selected.

MBD simulation :-

• After successfully assembling the valve train enable solidworks motion from solidworks Add-Ins for motion analysis.
• Add motor to the cam axis & set RPM to 1500.
• Add contacts to all the parts & assign material as Steel (Dry).
• Add linear spring in between valve & valve mount with spring stiffness of 10 N/mm^2 and free length of 45mm.
• To get smooth motion for study set frame rate to 7200. Also check the precise contact option.
• Run the simulation for desired time-interval.
• Plot the required results.

RESULT & DISCUSSION:-

note :- i.) Cam with camlift of 3.5mm = cam1

ii.) Cam with camlift of 6mm = cam2

1.) Valve Lift -

fig:- valve-lift for cam1 fig:- valve-lift for cam2

It can be seen that for cam2 valvelift is much more than that of cam1, i.e; for cam2 valve opens more than that of cam1. But for both the cam profile valvelift is consistent i.e; it opens equally for every cam rotation.

2.) Cam - Push_rod contact force :-

fig:- for cam1 fig:- for cam2

Contact force between cam & push_rod is constant throughout the simulation for cam1 and for cam2 it increases gradually & becomes max. when valve closes i.e; push_rod drops to cam.

3.) Push_rod - Rocker_Arm contact force :-

fig:- for cam1 fig:- for cam2

4.) Rocker_Arm - valve contact force (total) :-

fig:- for cam1 fig:- for cam2

5.) Rocker_Arm - valve contact force (X-component) :-

fig:- for cam1 fig:- for cam2

The contact force between rocker_arm & valve in X direction represents frictional force. As rocker_arm slides in right & left, the frictional force varies respectively. Therefore, graph varies both up (positive) & down (negative). The motion of rocker_arm to open the valve for cam2 is quite faster, therefore there is sudden rise in the frictional force.

ANIMATION :-

1.) Animation for Cam-1 assembly - 2.) Animation for Cam-2 assembly -

CONCLUSION :-

• As camlift is increased the amount by which valve opens also increases.
• The valve motion is mainly dependent on cam design.
• Increase in camlift causes increase in frictional forces.
• For both the cams motion of valve_train assembly is consistent.
• The total contact force between rocker_arm & valve is more than that of force in x direction, which produces valve motion.