MBD Simulation on IC Engine Valve Train

MBD Simulation on IC Engine Valve Train using SolidWorks

1. AIM : To analyse the motion study of IC Engine Valve Train using SolidWorks.

2. OBJECTIVE :

• To model all the parts of IC Engine Valve Train and assemble them.
• To 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

• To obtain the Valve Lift.
• To obtain the contact force between followings-
  1. Cam and Push Rod
  2. Push Rod and Rocker Arm
  3. Rocker Arm and Valve

• To 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.

3. INTRODUCTION :

3.1 Valve Train:- A valvetrain or valve train is a mechanical system that controls operation of the intake and exhaust valves in an internal combustion engine (IC Engine). The intake valves control the flow of air/fuel mixture (or air alone for direct-injected engines) into the combustion chamber, while the exhaust valves control the flow of spent exhaust gasses out of the combustion chamber once combustion is completed.

fig.1: IC Engine Valve Train

Valve Train consists of following components –

1. Cam
2. Push Rod
3. Rocker Arm
4. Valve
5. Valve Stump or, Valve Mount

Cam :- Camshaft makes contact on Cam; so that camshaft rotates.

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.

Push Rod :- 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 or, 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.

Valve :- Valve is a device used to close and open a passage. In motor vehicle engines, two engine valves are used for each cylinder-an inlet (or intake) valve and an exhaust valve.

3.2 Valve Lift : - The Valve lift is the distance by which the valve is raised from its seated position when it is fully opened.

The camshaft controls the speed of valve opening, valve lift off the valve seat, and how long the valve stays open.

The valve lift height and duration corresponds to the height and shape of the cam lobes.

3.3 Cam Lift : - This is the distance the cam lobe rises away from the base circle of the camshaft. It is the distance the lifter will move. It is also called "lobe lift".

4. PROCEDURE :

For performing motion analysis of Valve Train, we will need the 3D model of assembly of the Valve Train.

So, first we need to design 3D model of the followings –

1. Cam
2. Push Rod
3. Rocker Arm
4. Valve
5. Valve Mount

And for designing any 3D model, we have to design 2D sketch of the model first, after that we can proceed for designing 3D models.

• All the dimensions are in the unit system of MMGS (i.e. millimeter, gram, second).
• Front plane is used here for 2D sketch of all the parts.

5. CALCULATION :

FORMULA USED for Cam Lift :

Cam Lift can be derived from the sketch,

fig.2: example for cam lift formula

• 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"`

Now for,

Study- 1 (for cam lift = 3.5 mm)	Study- 2 (for cam lift = 6 mm)
Cam Lift = 3.5 mm D1 = 25 mm R1 = 12.5 mm D2 = 10 mm R2 = 5 mm Then by using Cam Lift formula, 3.5 = (L – 12.5) + 5 L = 11 mm	Cam Lift = 6 mm D1 = 25 mm R1 = 12.5 mm D2 = 10 mm R2 = 5 mm Then by using Cam Lift formula, 6 = (L – 12.5) + 5 L = 13.5 mm

6. 3D MODELS :

• Cam (3.5mm cam lift)

• Cam (6mm cam lift)

• Push Rod

• Rocker Arm

• Valve

• Valve Mount or, Valve Stump

• Assembly Design :

For performing assembly, we need to import the 3D model of parts which have to be assembled; here those model parts are as follows -

Part or, Model	Quantity
Cam	1
Push Rod	1
Rocker Arm	1
Valve	1
Valve Mount	1

fig.3: Valve Train

Material Selection –

• “Cast Carbon Steel” is selected as material for all the models or, parts of Valve train.

Motion Study :

• Motion study can be done in SolidWorks by using ‘Motion Analysis’ under ‘SolidWorks Motion’ option from ‘SolidWorks Add-Ins’ .

So, we are going to choose the ‘SolidWorks motion’ option from ‘SolidWorks Add-Ins’ and then going to ‘Motion Analysis’ option which we can find below in the SolidWorks window.

7. BODY OF CONTENT :

First make sure that none of the part or model is fixed, because every part of Valvetrain assembly will under some type of motion while working.

7.1 Study-1 (Motion Analysis for 3.5 mm Cam Lift)

Firstly, going to set up the motor at the center axis of Cam at a constant speed of 1500 rpm. And assigning the rotation of the motor as clockwise direction.

Providing a time frame for our motion study.

After that going to assign solid body contact by selecting contact option for all the parts by selecting two parts at a time which are going to be in contact with each other while simulation (or, motion) of assembly. There, we can also assign material to the models. So, here selecting ‘Steel (Dry)’ material for all the parts.

Now, setting up the number of frames per second equal to 7500 frames per second and also selecting precise contact for better visualization of simulation of assembly.

We will also provide gravity in Y direction (i.e. towards downward).

Now, adding the spring to the assembly as -

Now we will calculate the motion study.

• Simulation is runned for 0.3 second (it is going to follow same repetitive motion further).

Then, we will get the plots by clicking on result and plot section as –

fig.4: Linear Displacement Vs Time plot of Valve

fig.5: Contact Force Vs Time plot between Cam and Push Rod

fig.6: Contact Force Vs Time plot between Push rod and Rocker arm

fig.7: Contact Force Vs Time plot between Rocker Arm and Valve (measuring w.r.t. magnitude)

fig.8: Contact Force between Rocker Arm and Valve (measuring w.r.t. X-direction)

7.2 Study-2 (Motion Analysis for 6 mm Cam Lift)

Firstly, going to set up the motor at the center axis of Cam at a constant speed of 1500 rpm. And assigning the rotation of the motor as clockwise direction.

Providing a time frame for our motion study.

After that going to assign solid body contact by selecting contact option for all the parts by selecting two parts at a time which are going to be in contact with each other while simulation (or, motion) of assembly. There, we can also assign material to the models. So, here selecting ‘Steel (Dry)’ material for all the parts.

Now, setting up the number of frames per second equal to 7500 frames per second and also selecting precise contact for better visualization of simulation of assembly.

We will also provide gravity in Y direction (i.e. towards downward).

Now, adding the spring to the assembly as -

Now we will calculate the motion study.

• Simulation is runned for 0.3 second (it is going to follow same repetitive motion further).

Then, we will get the plots by clicking on result and plot section as –

fig.9: Linear Displacement Vs Time plot of Valve

fig.10: Contact Force Vs Time plot between Cam and Push Rod

fig.11: Contact Force Vs Time plot between Push rod and Rocker arm

fig.12: Contact Force Vs Time plot between Rocker Arm and Valve (measuring w.r.t. magnitude)

fig.13: Contact Force between Rocker Arm and Valve (measuring w.r.t. X-direction)

8. RESULTS :

8.1 Study-1 (Motion Analysis for 3.5 mm Cam Lift)

>>Valve Lift (Linear displacement of Valve)

>>Contact force between Cam and Push Rod

>>Contact force between Push Rod and Rocker Arm

>>Contact force between Rocker Arm and Valve (measuring w.r.t. magnitude)

>>Contact force between Rocker Arm and Valve (measuring w.r.t. X-direction)

8.2 Study-2 (Motion Analysis for 6 mm Cam Lift)

>>Valve Lift (Linear displacement of Valve)

>>Contact force between Cam and Push Rod

>>Contact force between Push Rod and Rocker Arm

>>Contact force between Rocker Arm and Valve (measuring w.r.t. magnitude)

>>Contact force between Rocker Arm and Valve (measuring w.r.t. X-direction)

• Animation Video

https://www.youtube.com/watch?v=V0YE3XTAhYE

• Drive link for 3D models, Results in Excel sheet : -

https://drive.google.com/file/d/1XWFhtIqCInmGt7SIWMUbEM0eMPPZZrgX/view?usp=sharing

9. ERROR :

• While selecting Spring of value, K = 10 N/mm & Free length = 40 mm –

The Valve left the contact with Rocker Arm while simulation of valve train. This happens due to the selection of the free length of spring with lesser value.

10. CONCLUSIONS :

1. Reasons due to which the Contact force between Rocker arm and Valve varies while measuring with respect to the X direction and measuring with respect to magnitude –
   1. Measuring the contact force with respect to magnitude, represents the net contact force between the two bodies. While contact force along X direction is frictional force between the two bodies which arises due to sliding of rocker arm surface over the valve head.
   2. The change in direction of frictional force occurs because while simulation of valvetrain; the rocker arm first slides towards back (i.e. origin or, negative of X-axis) and gives a positive friction force against the motion and after that rocker arm slides away from the origin gives rise to friction force in the negative X direction.
2. Free length of spring should be selected as such that the spring must be compressed in its initial state. And also, the pre-compression created in spring must be enough to always maintain the contact between Push rod and Valve.
3. If the value of contact force between the parts varies (or, fluctuates), then vibration generates in the assembly and will also cause failure of the valve train assembly.