MBD Simulation on IC Engine Valve Train
AIM: To calculate the valve lift & contact forces for given cam lift.
Objective:
To do motion analysis of the IC valve mechanism, considering different conditions and assigning the proper materials to the component.
Given Data:
| Sr No. | Cam Lift | Motor Speed |
| 1 |
3.5 |
1500 RPM |
| 2 |
6 |
1500 RPM |
To Calculate:
- Valve Lift.
- The contact force between Cam and Push Rod.
- The contact force between Pushrod and Rocker Arm.
- The contact force between Rocker Arm and Valve.
Introduction:
- Internal combustion engine valves are precision engine components. The valve train system is one of the major parts of internal combustion engine, which controls the amount of air-fuel mixture to be drawn into the cylinder and exhaust gas to be discharged.
- The fresh charge (air - fuel mixture in Spark Ignition Engines and air alone in Compression Ignition Engines) is induced through inlet valves and the products of combustion get discharged to
atmosphere through exhaust valves. - This seals the working space inside the cylinder against the manifolds.
- So design of valve lift profiles and valve train components is most important for the engine performance, valve train durability, and NVH.
- Therefore valve train system should be optimally designed so as to avoid an abnormal valve movement, such as valve jumping or bounce up to the maximum engine speed.
- There are different types of valves used by the manufactures; some common types of valves being poppet valves, slide valves, rotary valves and sleeve valve.
Formula to be used:
To calculate the centre distance between the circles, we will be using the cam lift formula.
CAM LIFT= (L - R1)+ R2
where, the L is the centre distance between the larger circle & the samlller circle.
The R1 is the radius of the larger circle.
The R2 is the radius of the smaller circle.
Modelling the components:
- Initially we will model the cam.
- To model the cam we have given initial conditions that are;
- The Cam lift = 3.5 for (case-1)
- The Cam lift = 6 for (case-2)
CAM:
(CASE - 1) The Cam lift = 3.5
To model the cam we will assume the the two diameters of the circle which will be used to draw the profile of the cam.
Let the two circle of diameters are 25 mm & 10 mm respectively.
Note draw the larger circle at the centre of the front plane & draw the smaller circle at the vertical axis above the larger circle.
To calculate the centre distance between the circles, we will be using the cam lift formula.
CAM LIFT= (L1 - R1)+ R2
where, the L1 is the centre distance between the larger circle & the samlller circle.
the R1 is the radius of the larger circle=12.5
the R2 is the radius of the smaller circle= 5
Calculation: (L1 - 12.5) + 5 = 3.5
therefore, L1 = 11 mm.
(CASE - 2) The Cam lift = 6
Similarly, we have to model the cam for case-2
Initially, we will assume the the two diameters of the circle which will be used to draw the profile of the cam.
Let the two circle of diameters are 25 mm & 10 mm respectively.
Note draw the larger circle at the centre of the front plane & draw the smaller circle at the vertical axis above the larger circle.
To calculate the centre distance between the circles, we will be using the cam lift formula.
CAM LIFT= (L2 - R1)+ R2
where, the L2 is the centre distance between the larger circle & the samlller circle.
the R1 is the radius of the larger circle.
the R2 is the radius of the smaller circle.
Calculation: (L2 - 12.5) + 5 = 6
therefore, L1 = 13.5 mm.
VALVE:
To model the valve we will draw a sketch on the front plane as shown below & then revolve 360 degree.
Rocker-Arm:
The rocker arm is modelled as per below dimension on the front plane.
Push Rod:
The push rod is modelled as per below dimension on the front plane.
Valve Mount:
The vlave mount is modelled as per below dimension on the front plane.
Assembling all the components:
- Insert the rocker arm first of all & make it float so that it can move freely.
- Coincide the axis of rocker-arm with front plane & right plane one by one respectively.
- Then coincide the front plane of rocker arm & front plane of assembly.
- Now, insert the cam in the assembly.
- Now, coincide the front plane of the cam with the front plane of assembly.
- Give a distance mate of 20 mm to the axis of the cam with the front plane of assembly.
- Provide a distance mate of 125 mm to the axis of the cam with the top plane of assembly.
- Now, insert the push rod in the assembly.
- Coincide the axis of the push rod with the front plane of assembly.
- Give a distance mate of 20 mm to the axis of the push rod with the front plane of assembly.
- Now, insert the valve mount in the assembly.
- Coincide the axis of the valve mount with the front plane of assembly.
- Give a distance mate of 50 mm to the axis of the valve mount with the front plane of assembly.
- Select the top face of valve mount & give a distance mate of 60 mm with the top plane.
- Now, insert the valve in the assembly.
- Now, coincide the axis of the valve with the front plane of assembly.
- Select the axis of the valve & axis of the valve mount & coincide both of them.
- Ensure that all the components just touch together by using physical dynamics option in Move component tool.
Motion Analysis:
- To do motion analysis, go to the Solidworks addin and select solidworks Motion.
- Then, select at the motion study 1, present at the bottom of the software window.
- Then change the animation to the motion analysis.
- Then add a motor to the axis of the cam & give the value equal to the 1500 RPM.
- Add contact between the adjacent & contacting components.
- Also, while giving contact, assign the material to the individual compnents.
- Assign Steel (Dry) material to all the components.
- Add a linear spring in between the valve mount edge & the edge of the valve.
- Give a pretension in the spring by changing it's free length from 35mm to 45mm.
- Change the spring stifness from 1 N/mm to 10 N/mm
- Now, select all the components & edit the material, assign the material to cast carbon steel.
- Now, Change the frame per seconds from 25 to 7200 FPS.
- Select Precise contact.
Plots for Case 1:
Valve Lift: The position of the valve lift during any time can be evaluated by using the below plot.
Contact Force between Cam & Push Rod:
The cotact force between the cam & push rod can be easily evaluated during any time can be evaluated by using the below plot.
Contact Force between Push Rod & Rocker arm:
The cotact force between the push rod & rocker arm can be easily evaluated during any time can be evaluated by using the below plot.
Contact Force between Rocker arm & Valve: (magnitude)
The cotact force between the rocker arm & valve can be easily evaluated during any time can be evaluated by using the below plot.
Contact Force between Rocker arm & Valve: (with respect to X-axis only)
The cotact force between the rocker arm & valve can be easily evaluated during any time can be evaluated by using the below plot.
Results for Case-1:
The Valve lift obtained for the case-1, when the cam lift is 3.5 is calculated & found to be 9 mm.
The contact Force between Cam & Push Rod is found to be 1210 N.
The Contact Force between Push Rod & Rocker arm is found to be 1211 N.
The Contact Force between Rocker arm & Valve is found to be 277 N. (magnitude)
The Contact Force between Rocker arm & Valve is found to be 52 N. (X-component)
Plots for Case -2:
Valve Lift: The position of the valve lift during any time can be evaluated by using the below plot.
Contact Force between Cam & Push Rod:
The cotact force between the cam & push rod can be easily evaluated during any time can be evaluated by using the below plot.
Contact Force between Push Rod & Rocker arm:(case-2)
The cotact force between the push rod & rocker arm can be easily evaluated during any time can be evaluated by using the below plot.
Contact Force between Rocker arm & Valve: (magnitude)
The cotact force between the rocker arm & valve can be easily evaluated during any time can be evaluated by using the below plot.
Contact Force between Rocker arm & Valve: (with respect to X-axis only)
The cotact force between the rocker arm & valve can be easily evaluated during any time can be evaluated by using the below plot.
Results for Case-2:
The Valve lift obtained for the case-1, when the cam lift is 6 is calculated & found to be 15 mm.
The contact Force between Cam & Push Rod is found to be 14604 N.
The Contact Force between Push Rod & Rocker arm is found to be 14774 N.
The Contact Force between Rocker arm & Valve is found to be 2819 N. (magnitude)
The Contact Force between Rocker arm & Valve is found to be 72 N. (X-component)
Why there is Difference between the contact forces while considering magnitude & while considering X-axis only ?
There is a wide difference between the contact forces bwtween the rocker arm & valve while considering with maginitude & with X axis only because in magnitude we are dealing with the three forces in three different direction namely, X, Y & Z axis. While motion anakysis it is found that there is also a contact force in the Y & Z direction too.That is why we got a difference in the contact forces.
Conclusion:
I have obtained the motion analysis while considering two different cases.
The contact forces & the valve lift for case-2 is much larger than the case-1.
So, while increasing the cam lift there is increase in the valve lift & the contact forces.
Link for the Animation of the IC Valve Mechanism: