MBD Simulation on IC Engine Valve Train
AIM: To model the parts and assemble of IC Engine Valve Train in SolidWorks.
OBJECTIVES:
- To make 3d model of the all the components of valve train.
- To make the assembly using all the parts
- To perform motion analysis by rotating crank at 1500 rpm for 3 different conditions.
- To obtain the valve lift
- To obtain the contact force between Cam and Push Rod, Pushrod and Rocker Arm, Rocker Arm and Valve.
INTRODUCTION:
- Valves are used to allow the flow of fuel-air mixture to the combustion chamber(inlet valves) and to deliver the burnt gas from the combustion chamber (exhaust valve)
- These valves are mounted on the cylinder's head
- These are initially closed with the help of springs
- With the help of cam in the camshaft, these valves are open to perform their respective work
- Rocker arm mechanism is also used to open and close the inlet and exhaust valves
- One end of the rocker arm is connected to the follower which has a direct contact with cam
- Usually the middle point of the rocker arm is rigid due to which it can oscillates like see-saw
- When the follower moves upward, rocker arm's one end moves upward whereas the other end moves downward by this valve is opened.
INPUTS and CALULATION:
Cam lift can be calculated as:
- The diameter of lower circle (D1) – 35 mm
- The diameter of Upper circle (D1) – 20 mm
- The distance between two Centers (L) – 30 mm
CAM LIFT = (L-R1) +R2
- For 3.5 mm cam lift
D1=25mm R1=12.5
D2=10mm R2=5
L=3.5-5+12.5 =11
- For 6 mm cam lift
D1=25mm R1=12.5
D2=10mm R2=5
L=6-5+12.5 =13.5
3D MODELS:
- Cam
An oval or egg shaped wheel which when rotating, coverts circular motion into reciprocating motion. This cam is a part of the rotating shaft that helps open and close valves in piston engine
- 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
A rocker arm is a pivoting lever that pushes on the valve stem. Rocker arms will sometimes be called rocker levers, or just rockers. Depending on the type of valve train, the rotating camshaft lobes will either push directly on the rocker arm, or on the pushrods, which will conduct the motion up to the rocker arm. In an overhead cam engine, the cam follower is built into the rocker arm in the form of a roller.
- Valve
A valve is composed of two major sections, the valve head, and the valve stem. The head of the valve is what allows air into and out of the cylinder. The stem is what gets pressed on by the rest of the valve train. At the end of the stem are grooves that keepers will fit into to hold the valve in place. Some engines have only two valves per cylinder, and some have four. The more common number in the heavy-duty diesel market is four. These are split evenly between the intake and exhaust valves.
- Valve mount
This acts as the stoppage for the valve and limits the movement of the valve.
- Assembly of valve train
SETUP EXPLANATION:
- Here the first thing we start with is designing of the components of valve train.
- The first component we design is Cam, here we draw a profile of cam on front plane and then extrude it. There are two cases for the cam I.e. 3.5mm cam lift and 6 mm cam lift
- Then we make the push rod, here we draw a profile of push rod such that it can be revolved and we are able to get a pushrod.
- Further we make the rocker arm, Here also we draw the profile of the rocker arm in front plane and then extrude it.
- Further for the valve and valve train also by making a proper profile and then using revolve command we are able to get the component ready.
- Then in the front plane we make the assembly of the valve train using the above components. In addition to this we change the material of assembly to cast carbon steel.
- Further after making the assembly we go for the motion analysis where we set the motor at speed of 1500 rpm on the cam for rotation of cam.
- Then we select the components for solid body contact.
- Further we set the frames per second to 7200 and also select the precision contact option.
- Then we add the spring on the valve where we keep the spring constant as 10 N/mm and then calculate and do the analysis.
- After the calculation is done we plot the different required graphs.
- This analysis is carried out for two different cases i.e. 3.5mm and 6mm cam lift. So based on these cases the design of cam is varied and then the analysis is done.
OUTPUT PLOTS:
CASE 1: To perform motion analysis for 3.5 mm Cam-lift
- 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 rocker arm and valve x direction(3.5 mm lift)
CASE 2: To perform motion analysis for 6 mm Cam-lift
- 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 rocker arm and valve x direction(6 mm lift)
Animation:
Conclusion:
- The contact forces are at their peaks when the cam lobe is at its topmost position.
- The contact force between each component and linear displacement of the valve for the cam lift of 6 mm is larger than the cam lift of 3.5mm,this shows that the cam geometry affects the amount of opening of valve .
- Contact force between rocker arm and the valve with respect to magnitude and X direction varies, for the x component of contact force we get negative force because the rocker arm slides both forward and backward during one complete rotation of the cam and hence the friction force acts in both direction.
Drive Link:
https://drive.google.com/drive/folders/1Ry1PbukNmCTFxJuLCJkwHnFYD7TD2CHv