MBD Simulation on IC Engine Valve Train

Objective:

The main objective is to model and assemble IC engine valve train which consists of essential parts such as a cam, push rod, rocker arm, valve mount, and valve and run the motion analysis to find the contact force encountered between the parts and explain the results.

Introduction:

A valve train is a mechanical system that controls the operation of the valves in an internal combustion engine, whereby a sequence of components transmits motion throughout the assembly. A conventional reciprocating internal combustion engine uses valves to control the flow of the air/fuel admix into and out of the combustion chamber.

A typical valvetrain consists of valves, rocker arms, pushrods, lifters, and cam. Valvetrain opening/closing and duration, as well as the geometry of the valvetrain, controls the amount of air and fuel entering the combustion chamber at any given point in time. Valvetrains are built in several configurations, each of which varies slightly in layout but still performs the task of opening and closing the valves at the time necessary for proper operation of the engine.

Components use in ic engine valve train:

1. 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 (e.g. an eccentric wheel) or shaft (e.g. a cylinder with an irregular shape) that strikes a lever at one or more points on its circular path.

2. PUSHROD -Pushrods are long, slender metal rods that are used in overhead valve engines to transfer motion from the camshaft to the valve

3.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.

4. 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).

5.Valve mount: -It is a type of hollow cylinder which provides the constrains to the engine valve. By using it the valve only can slide into the cylinder. It has a cap which is used to fixed the spring to follow back the motion valve.

Motion analysis:

1.To run the motion analysis go to motion study and establish contact between Cam-push rod, pushrod-rocker arm, rocker arm-valve.

2.Next, give the rotation to the cam with 1500 RPM.

3.Set up a linear spring between the valve and the valve stem with the spring stiffness of 10 N/mm and free length 45mm.

4.Change the frames to 9000 frames per sec and use precise contact.

5.Select the entire assembly and assign the material as Cast Carbon Steel and click apply. Now click the calculation button. Run the analysis for 0.2 sec.

Cam lift formula:

Case 1: 3.5 mm Lift

Cam Lift = (L-R₁) + R₂

L= CAM Lift - R₂ + R₁

In our case R₁=12.5 mm and R₂= 5 mm

For 3.5 mm cam lift

L= 3.5-5+12.5 =11 mm

Plots:

1. Valve Displacement

2. Contact Force

Contact Force b/w CAM & Push Rod

Contact Force b/w Push Rod & Rocker Arm:

Contact Forc b/w Rocker Arm & Valve:

Case 2: 6mm Lift

For 6 mm cam lift

L= 6-5+12.5 =13.5 mm

Plots:

1.Valve dsiplacement

2. Contact Force

Contact Force b/w CAM & Push Rod:

Contact Force b/w Push Rod & Rocker Arm:

Contact Force b/w Rocker Arm & Valve

Conclusion:

• As we Increased CAM lift, Valve Displacement is increased.
• Valve lift is mainly depends on the Design of CAM and Rocker Arm.
• Suitable spring (free length & Spring constant) plays a vital role in Valve lift.
• The contact force between the Rocker arm and valve varies while measuring with respect to the X direction and measuring with respect to magnitude because magnitude is the result force of all the X, Y and Z direction. So, it is differing from only in x direction.

Animation: