MBD Simulation on IC Engine Valve Train
AIM: To study the motion analysis of IC engine valve train
Theoritical background:
A 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 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 valve train of an internal combustion engine includes components required to control the flow of gases into and out of the combustion chamber. This includes valves and related components required to allow the air-fuel mixture to enter the combustion chamber, seal the combustion chamber during compression and combustion, and evacuate exhaust gases when combustion is complete. The type of valve train used for a reciprocating engine depends on the engine design and whether the engine is a four-stroke cycle or two-stroke cycle unit.
Solid Modelling of the Components of Valve train
1. Rocker Arm 2. Cam 3. Valve
4. Valve Mount 5. Push rod
Assembled View
We have to perform motion study for below 2 different cases of cam lift
2D diagram of the CAM is given below
Case 1: CAM lift = 3.5 mm Case 2: CAM lift = 6 mm
Assembeled View
Motion Analysis:
Motion analysis of valve train is carried out for 2 different cases of CAM lift as mentioned above
Steps:
1. After obtaining the required assembly, go to motion study section in the solid works and set up the motor to 1500 rpm at the CAM.
2. Go to the contact selection, then select the surfaces which are in contact with each other then appy the material as "dry steel" to all the components.
3. Go to motion study properties and select the motion analysis. Run the study for the set time limit.
4. Export the results of linear displacement of the valve and Contact forces between required components.
CASE 1: CAM lift = 3.5 mm
1. Linear displacement of Valve
2. The contact force between Cam and Push Rod
3. The contact force between Push Rod and Rocker arm
4. The contact force between Rocker arm and Valve
5. The contact force(x-direction) between Rocker arm and Valve
CASE 2: CAM lift = 6 mm
1. Linear displacement of Valve
2. The contact force between Cam and Push Rod
3. The contact force between Push Rod and Rocker arm
4. The contact force between Rocker arm and Valve
5. The contact force(x-direction) between Rocker arm and Valve
TABULATION:
The results from the plots of the above 2 cases are tabulated below
Observations and Conclusions:
The valve displacement is more in case when the CAM lift is 6mm when compared to the first case. The Contact Force between the respective components are more with increase in CAM lift because the CAM pushes the push rod with more force due to increase in the distance between the centres of the circles. More CAM lift means the valve will open further. Increasing CAM lift will allow more air or exhaust to move through an engine. Increasing valve lift improves airflow up to a point. But airflow eventually peaks out because of restrictions in the cylinder head, intake or exhaust system.
The Contact Force between the rocker arm and valve varies while measuring with respect to magnitude and measuring with respect to x direction. During one complete rotation of CAM the rocker arm slides up and down, the x-component achieves negative force and friction acts in both direction. The Contact Force magnitude pushes the valve downwards but the x-component of the contact force gives the friction force acting between the rocker arm and valve.