MBD Simulation on IC Engine Valve Train
Aim:To create 3D models for IC engine valve train assembley.
Objective:
- Model the parts and assemble them in SolidWorks.
- Run the simulation using the below parameters
| Sl.No | CAM Lift (mm) | Speed (RPM) | Material |
| 1 | 3.5 | 1500 | Cast Carbon Steel |
| 2 | 6 | 1500 |
Cast Carbon Steel |
Obtain the
- Valve Lift.
- The contact force between
- Cam and Push Rod
- Pushrod and Rocker Arm
- Rocker Arm and Valve
Theory:
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, 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:
1. sketching and 3D modelling components:
For sketching the different cam lifts the below formulae are used:
CAM Lift Formula
CAM Lift can be derived from the sketch
● The diameter of lower circle (D1)- 35 mm
● The diameter of upper circle (D2)- 20 mm
● The distance between two centres (L)- 30 mm
CAM Lift = (L-R1)+R2
for case 1,cam lift 3.5mm,
3.5=(l1-17.5)+10
l1=11mm
for case 2,cam lift 6mm,
6=(l2-17.5)+10
l2=13.5mm
Design of cam for first case 1-
Design of cam for case 2:
Design of rocker arm:
Design of valve:
Design of Valve stem:
Design of pushrod:
2.Assembley of components:
All the components are assembled as per the required constraint.All components were brought to front plane and made coincident to this plane.The cam was also positioned by also making its axis xoincident to yhe top plane and right plane.Distance mate were provided to other component so that they donot obstruct each other during the motion and the axes of valve stem were made coincident.Top plane of the rocker arm and the assembley were provided an additional angle mate of 0 degree so that it remains parallel to the plane.After successful assembley,it was made to move using physical dynamics so that necessary clearance and contact are provided between the components.
3.Motion study:
case1(for cam lift of 3.5mm):
A torque of 1500rpm is provided to the cam axis.The material for all the parts were selected to be steel(dry).A linear spring of of spring constant k as 15N/mm is provided between the upper edge of valve stem and the lover stem of the valve.The spring was pretensioned by changing its natural length to 45mm.For solving the study more accurately 9000fps were provided with precise contact.By selecting the complete assembley the material specified was Cast Carbon Steel.
plot for linear displacement of valve:
plot for contact force between cam and pushrod:
Plot for contact force between pushrod and Rocker Arm:
Plot for contact force between pushrod and Rocker Arm:
Case 2(for cam lift of 6mm):
A torque of 1500rpm is provided to the cam axis.The material for all the parts were selected to be steel(dry).A linear spring of of spring constant k as 15N/mm is provided between the upper edge of valve stem and the lover stem of the valve.The spring was pretensioned by changing its natural length to 50mm.For solving the study more accurately 9000fps were provided with precise contact.By selecting the complete assembley the material specified was Cast Carbon Steel.
Plot for linear displacement of valve:
plot for contact force between cam and pushrod:
Plot for contact force between pushrod and Rocker Arm:
Plot for contact force between valve and Rocker Arm:
The lift during the motion was obtained from the excel spreadsheetand was 53.815mm for maximum and 50.253mm for minimum.The difference between the two positions was 3.562mm.
Q.Explain why the contact force between the Rocker arm and valve varies while measuring with respect to the X direction and measuring with respect to magnitude
A.It is because the contact force line of action is changing continuously and along the X axis the surface of valve and the rocker arm rubs over each other and produces friction between them and is both positive and negative as obtained in the plots.This frictional force tend to losses in energy and will dissipate as heat.Whereas the contact force magnitude calculates vector sum of forces in all 3 directions and will be greater than forces in either directions.
For case 1 comparisoin of contact forces
For case 1 comparisoin of contact forces
- The 3D model,assembley,simulation of case 1and case2 can be found here:https://drive.google.com/drive/folders/1hj1dcz4QOUYo276MH2AjhxVzJNvGYUin?usp=sharing
- The animation video link:
- https://youtu.be/YCWzSa43Gxs
- https://youtu.be/QBnOWK_hE5M
Conclusion:
The above are the all plots ,graphs and the required analysis which was required to deal with this project.