MBD Simulation on IC Engine Valve Train
Aim:Study of Cam and follower mechanism.
Theory:- Cam follower are higher pair mechanism.They can be use to produce any type of periodic motion of follower from rotary motion of cam.
Cam follower are type of 3 bar mechanism .
List of Link
Link1:-Fixed Link
Link2:Cam
Link3:-Follower
List of Contact
Revolute Pair between link 1 and 2
Line Contact between link 2 and 3
Sliding contact between link 3 and link 1
Cam and follower are used to IC engine to open and close valve periodically.There are several standard follower profiles ,they include
1.Simple Harmonic Motion
2.Uniform Velocity
3.Uniform Acceleration and Uniform De-acceleration
4.Cycloid
Any of the various profile could be used for follower movement however,This increases complications in Manufacturing of Cam .Thus there are several different standard countour of Cam profile which are combination of several standard shapes such as circle ,lines,etc
Some of the standard profile include
1. Tangent Cam
2. Concave Cam
In the following study tangent Cam with flat face follower is used to study it's displacement diagram and various contact force for two case study of lift.
Speed of Rotation= 1500 rpm
Material of Cam:- Cast Carbon Steel
Base Circle Radius:- 12.5mm
Nose Circle Radius:- 5mm
Simulation of the entire assembly
Case1: Lift :- 3.5mm
Graph Representating Valve Lift
Graph Representating contact Force between Cam and Push Rod
Graph Representating contact Force between Pushrod and Rocker Arm
Graph Representating contact Force between Rocker Arm and Valve(Magnitude)
Graph Representating contact Force between Rocker Arm and Valve(X-axis)
Case2: Lift :- 6mm
Graph Representating Valve Lift
Graph Representating contact Force between Cam and Push Rod
Contact force developed between cam and followers are function of Inertia,Displacement,Spring Preload.Therefore
Contact Force=m*a(Inertia)+k*x(Displacement)+P(Preload in spring)
In the above graph you can see three spikes.They are not some random spike due to vibrations or spring surge.
The First Spike represents the rise of the follower.During the rise the follower must overcome 1. Preload 2. The Spring Restoring Force 3.Due to Inertia.
Therefore it is the largest.On the other hand in the second spike.We know that the component of Inertia depends on the acceleration of follower.i.e greater the acceleration greater is the force.This is the very reason the first spike is greater then the secong because Solidworks accelerates faster when travelling on the tangent as compared to the nose.
The Last spike is greater then the second because now it again has greater interia but now the restoring force is decreasing as it is returing.
From the above graph one can clearly see the impact of Inertia on design of Cam.
Graph Representating contact Force between Pushrod and Rocker Arm
Graph Representating contact Force between Rocker Arm and Valve(Magnitude)
Graph Representating contact Force between Rocker Arm and Valve(X-axis)
Conclusion
For the study of 2 Cases 3 graphs where observed
1. Graph representating the Linear displacement
-
In a Cam follower mechanism lift is the radial distance of the follower from the centre of rotation of cam.So,lift of 6mm means the follower must have an maximum displacement of 6mm i.e at the nose of the cam.
- Here in the graph is not the corresponding lift because there is a rocker in between which acts as a lever and thus the valve lift is always greater than the follower lift and also with mechanical advantage.
2.Graph Representating contact Force between Cam and Push Rod
- It shows the variation in contact force it was explained below the 6mm graph
3.Graph Representating contact Force between Rocker An Valve
- The Graph which shows magnitude and along x axis are different
- Because the force along the X axis is friction and Along the Y is the normal contact.