MBD Simulation on IC Engine Valve Train
AIM: To design a 3D model of an IC Engine Valve Train and perform the motion analysis for different cam lift values.
THEORY:
A valvetrain or 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.
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.
1. 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.
2. 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.
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. Valve
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).
OBJECTIVES:
1. To study the motion of an IC Engine Valve Train.
2. To obtain the displacement curve of the valve lift.
3. To obtain the contact force between Cam and Pushrod, Pushrod and Rocker Arm, Rocker Arm and Valve.
STEPS:
1. Design the CAD models of every component separately in SOLIDWORKS.
2. Use the below formula to calculate the dimensions of the Cam for desired cam lift.
3. Assemble all the components for motion study.
4. In motion study window, add a motor of 1500 RPM to the cam axis, provide an fps of 9000 so that every degree of cam movement is captured.
5. Define solid contacts between components.
6. Add a spring in between valve head and valve mount and specify the spring properties.
7. Change the material of all components to Cast Carbon Steel.
8. Calculate the motion study and obtain the desired plots.
DESIGNING:
2-D sketch
1. Cam of 3.5 mm lift.
2. Cam of 6 mm lift.
3-D models
1. Cam of 3.5 mm lift.
2. Cam of 6 mm lift.
3. Pushrod
4. Rocker Arm
5. Valve
6. Valve mount
Assembly Models-
1. Cam of 3.5 mm lift.
2. Cam of 6 mm lift.
SIMULATION RESULTS:
1. Cam of 3.5 mm lift.
a) Linear Displacement of Valve lift
b) Contact Force between Cam and Pushrod
c) Contact Force between Pushrod and Rocker Arm
d) Contact Force between Rocker Arm and Valve
e) Contact Force between Rocker Arm and Valve in the x-direction
2. Cam of 6 mm lift.
a) Linear Displacement of Valve lift
b) Contact Force between Cam and Pushrod
c) Contact Force between Pushrod and Rocker Arm
d) Contact Force between Rocker Arm and Valve
e) Contact Force between Rocker Arm and Valve in the x-direction
ANIMATIONS:
1. Cam of 3.5 mm lift.
2. Cam of 6 mm lift.
CAD MODEL FILES:
https://drive.google.com/drive/folders/1AF5VpdVhjwG8LdybjAi6iwIYPByOnAr8?usp=sharing
CONCLUSION and EXPLAINATION:
From the plots of linear displacement of Valve lift, Valve lift increases as cam lift increases.
From the plots of contact forces, contact force also increases with increase in cam lift.
The contacts force between the Rocker arm and valve varies while measuring with respect to the X-direction and measuring with respect to magnitude because rocker Arm applies force in both x and y-direction and magnitude is the resultant of x and y component of forces.
REFERENCES:
1. Wikipedia - https://en.wikipedia.org/wiki/Valvetrain