MBD Simulation on IC Engine Valve Train
AIM: To create a 3D CAD model of the IC Engine Valvetrain and to do motion analysis.
THEORY: A valve train is a mechanical system that controls the 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 combustion chamber once combustion is completed. [1]
Components
The valve train 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 the 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/bucket tappet
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 to actuate the valves. [2]
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 valve train at high engine speeds. [3]
DESIGN: The 3D CAD models are designed in SolidWorks and motion analysis is analyzed on Motion Analysis add-on in SolidWorks. The following steps were taken to design the mechanism:-
Step-1: First, a 2D sketch of Cam was designed and then extruded.
Step-2: Second, a 2D sketch of Pushrod was designed and then extruded.
Step-3: Third, a 2D sketch of Rocker arm was designed and then extruded.
Step-4: Forth, a 2D sketch of Valve was designed and then extruded.
Step-5: Fifth, a 2D sketch of Valve mount was designed and then extruded.
Step-6: Then all parts models were assembled, and constraints were provided.
MOTION ANALYSIS:
Motion analysis was conducted using the Motion Analysis add-on in SolidWorks. The motion features of the SolidWorks provide us a wide range of motion study, they can be divided into three categories:
Animation: If one simply wishes to create some nice visuals for presentation or marketing without consideration of mass and gravity effects, then animation is perfect for it.
Basic Motion: For an extra layer of complexity that takes into consideration the effects of mass, springs, gravity, and physical collision detection, then a Basic Motion study is more suited for the requirements.
Motion Analysis: This is the top tier of motion study and takes into account a wider range of physical interactions such as impact effects, damping, force, momentum, etc. [2]
Step-1: Motion Study 1
Cam lift = 3.5mm
The following plots were generated
i) Contact Force between Cam and Pushrod
ii) Contact Force between pushrod and Rocker arm
iii) Contact Force between Rocker arm and Valve
iv) Linear displacement of Valve
Step-2: Motion Study 2
Cam lift = 6mm
The following plots were generated.
i) Contact Force between Cam and Pushrod
ii) Contact Force between Pushrod and Rocker arm
iii) Contact Force between Rocker arm and Valve
iv) The linear displacement of Valve
v) X-component of Contact force between Rocker arm and Valve
The contact force graph between the valve and rocker arm in direction x shows the movement of rocker arm and valve on the line contact. Inline contact between the valve and the rocker arm are due to the action of force applied by spring which opposes the rocker arm movement means resist to move the valve in a downward direction. The resistance of the movement of the valve offered by the spring to the valve tends to push back the valve in the original position. The resistance to movement of the valve the graph of contact force shows the negative force on the rocker arm, As well as the force in the x-direction of between the rocker arm and valve, changes the position along the surface of the valve in the x-direction. As the graph shows the negative force are due to the movement of the point contact of the rocker arm to valve arm changes the point of contact.
That’s why the graph shows the negative direction of the force.
CONCLUSION:
Increasing the Cam lift increases the linear displacement of Valve.
Google drive link for the models:
https://drive.google.com/drive/folders/1yWtP9_rKH3mF977KtmMfyVgM36NpHsZz?usp=sharing
REFERENCES:
[1] Brain, Marshall (5 April 2000). "How Car Engines Work". HowStuffWorks. Retrieved 29 January 2014.
[2] "What is the difference between OHV, OHC, SOHC and DOHC engines?". www.samarins.com. Retrieved 23 January 2020.
[3] Cranswick, Marc (2011). The Cars of American Motors: An Illustrated History. McFarland. p. 80. ISBN 9780786446728. Retrieved 29 January 2014.