DESIGN AND MOTION ANALYSIS OF IC ENGINE VALVE TRAIN (using SOLIDWORKS)
AIM:
To design and perfotm motion analysis of an IC engine valve train of different cam-lifts using SOLIDWORKS
OBJECTIVES:
- To understand the working of an IC engine valve train
- To understand how different cam-lifts can affect the working of the valve train
- To analyze the above using SOLIDWORKS
INTRODUCTION:
A valvetrain or valve train is a mechanical 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.
Components:
- 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.
- Push-rod: 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: 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, 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).
PROCEDURE OF COMPLETION:
- The overall calculation of all the components were made.
- The length of the cam was calculated using the Cam-Lift Formula:
3. For CAM-lift = `3.5 mm`, R1 = `12.5 mm` and R2 = `5 mm`
L = `10.5 mm`
For CAM-lift = `6 mm`, R1 = `12.5 mm` and R2 = `5 mm`
L = `13.5 mm`
4. After all the calculations were made, the design was made using SOLIDWORKS.
5. Then, cast carbon steel material was used for better visualisation of the motion. The properties of the material are as follows:
| PROPERTY | VALUE | UNITS |
| Elastic modulus | 2e+11 | N/m^2 |
| Poisson's Ratio | 0.32 | N/A |
| Shear modulus | 7.6e+10 | N/m^2 |
| Mass density | 7800 | kg/m^3 |
| Tensile strength | 482549000 | N/m^2 |
| Compressive strength | - | N/m^2 |
| Yield strength | 248168000 | N/m^2 |
| Thermal Expansion cofficient | 1.2e-05 | /K |
| Thermal conductivity | 30 | W/(m-K) |
| Specific heat | 500 | J/(kg-K) |
| Mass damping ratio | - | N/A |
6. Then, RPM was set to 1500 and given to the cam and a spring with spring constant 10 N/m was installed between the valve and the valve mount.
OBSERVATIONS:
For `3.5mm` CAM-lift,
The motion of the valve train can be seen through the following link:
Linear Displacement of the Valve Lift:
Contact force between cam and push-rod:
Contact force between push-rod and rocker-arm:
Contact force between rocker-arm and valve:
Contact force between rocker-arm and valve in x-direction:
For `6mm` CAM-lift,
The motion of the valve train can be seen through the following link:
Linear Displacement of the valve lift:
Contact force between cam and push-rod:
Contact force between push-rod and rocker-arm:
Contact force between rocker-arm and valve:
Contact force between rocker-arm and valve in x-direction:
DESIGN AND ASSEMBLY OF THE VALVE TRAINS:
The design and the assembly can be seen through the following link:
https://drive.google.com/drive/folders/1vKhUex_EgXhkx666Vpa-w3Hi4PFGj8Sn
CONCLUSIONS:
- We can observe thatt more the CAM-lift, more is the linear displacement of the valve lift.
- The contact force between different components also increases with increase in CAM-lift.
- In CAM-lift = `3.5mm`, there is a difference in the total magnitude of the contact force between rocker-arm and valves and the contact force in the x-direction because in the x-direction, the frictional force acts which helps in sliding of the rocker-arm on the valves. Hence, it is both in positive and negative direction. But, the total magnitude only pushes the rocker-arm downwards. The fricitional force between the two surfaces can be shown as below:
We could see the magnitude of the friction force and the contact force between the rocker-arm and the valves in the x-direction are almost similar.
- Same is the case in the CAM-lift = `6 mm`.