MBD Simulation of IC Engine Valve Train
OBJECTIVE :
1. To Model IC Engine Valve Train using SOLIDWORKS.
2. To Simulate its motion.
3. To perform its motion analysis and obtain valve lift profiles for the given values of cam lifts.
4. To obtain plots of contact force between -
- Cam and Push Rod
- Push Rod and Rocker Arm
- Rocker Arm and Valve
INTRODUCTION :
A valvetrain or valve train is a system that controls 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 combusion chamber once combustion is completed.
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.
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.
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 in order to actuate the valves.
Valves
Most modern engines use poppet valves type. These are typically opened by the camshaft lobe or rocker arm, and closed by a coiled spring called a valve spring.
SIMULATION CASES :
| Cam Lift (mm) | Speed (rpm) | Material | |
| Case 1 | 3.5 | 1500 | Cast Carbon Steel |
| Case 2 | 6 | 1500 | Cast Carbon Steel |
PARTS :
Cam :
Cam profile is sketched according to the given cam lift. And then 'Extrude' command is used to give it depth.
Case 1:
Case 2:
Push Rod :
Push Rod is sketched accordingly and then revolved.
Rocker Arm :
Sketch is made and then extruded.
Valve :
Valve is sketched and 'Revolve' command is used to rotate it about the central axis.
Valve Mount :
Similarly, here also sketch is made followed by the use of 'Revolve Command'.
ASSEMBLY :
Now, all the parts are assembled using proper mates.
Case 1:
Case 2 :
Now, material is selected as Plain Carbon Steel. Material properties are predefined in Solidworks as shown below.
Now, motor is set to rotate at the cam axis at 1500 rpm using Motion Ananlysis.
Appropriate contacts are set.
Gravity is defined in the Y- axis downward.
A spring (of spring constant 10 N/mm) is set between the valve mount and valve head.
Now finally the simulatoin is calculated and the required plots are obtained.
RESULTS :
Here is the slow motioned video animation of the simulation -
Animation of Case 1:
Animation Of Case 2:
PLOTS :
Case 1:
Valve Lift Profile :
Contact Force Between Cam and Push Rod :
Contact Force Between Push Rod and Rocker Arm :
Contact Force Between Rocker Arm and Valve - Magnitude :
Contact Force Between Rocker Arm and Valve - X Component :
Case 2:
Valve Lift Profile :
Contact Force Between Cam and Push Rod :
Contact Force Between Push Rod and Rocker Arm :
Contact Force Between Rocker Arm and Valve - Magnitude :
Contact Force Between Rocker Arm and Valve - X Component :
CONCLUSION :
The Contact Force between Rocker Arm and Valve varies while measuring with respect to the X Direction and measuring with respect to Magnitude as the result in case of X Direction depicts Negative Values due to Frictional Contact. But while measuring and plotting the Magnitude of Contact Force, the direction is not kept in mind and the Contact Line performs a to and fro motion in vertical direction which negates the need for measuring the direction. Hence, output comes out to be Positive.
The Motion Analysis gives a satisfactory idea about the functioning of the IC Engine Valve Train wherein further scope of improvements exist to make it more smooth and efficient.
NOTE : The Part and Assembly Files can be accessed here - https://drive.google.com/drive/folders/19eGQEMqrBZCC-mzwAogX1P4tFXOKfg5H?usp=sharing
REFERENCES :
- https://en.wikipedia.org/wiki/Valvetrain#:~:text=A%20valvetrain%20or%20valve%20train,in%20an%20internal%20combustion%20engine.
- https://www.tvsmotor.com/blog/ohv-sohc-and-dohc-valve-trains/
========THANK YOU =========