MBD Simulation on IC Engine Valve Train

Aim: MBD SIMULATION ON IC ENGINE VALVE TRAIN AND DO MOTION STUDY TO FIND CONTACT FORCE AT DIFFERENT CONDITION ALONG WITH VALVE LIFT.

Introduction:

What is IC Engine Valve Train?

: A valvetrain or valve train is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion 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.

Parts:

1. Cam:

The timing and lift profile of the valve opening events are controlled by the cam, which is a carefully shaped lobe on a rotating shaft. The cam is driven by the crankshaft and— in the case of a four-stroke engine— rotates at half the speed of the crankshaft.

2. 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.

3. Rocker Arm:

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.

4. Valve:

The valve is typically opened by the camshaft lobe or rocker arm, and closed by a coiled spring called a valve spring.

5. Valve Mount:

As the name says, it is used to mount the valve along with spring, otherwise, the valve will not be in tension in the close state and it may leave the opening during the closed state as well.

6. Spring:

It is a very important component to retain the position of valve as it should be lost while in closing state and it also needs to get back to its locked position after the valve opening.

Application:

As the name suggests, it is used in an IC engine or any machine where we need to control the flow of fluid by the inversion of angle.

Objective:

To run the simulation using the below parameters:-

SR. NO.	Cam Lift (mm)	Speed (RPM)	Material
1	3.5	1500	Cast Carbon Steel
2	6	1500	Cast Carbon Steel

To obtain the:-

1.Valve Lift.

The contact force between:-

1.Cam and Push Rod

2.Pushrod and Rocker Arm

3.Rocker Arm and Valve

The contact force between the Rocker arm and valve with respect to the X-direction and measuring with respect to magnitude.

Design:

Below are the screenshot attached for the 3D model design. (ref: Skill-Lync)

GIVEN:

Solidworks Part Design Procedure:

For each part, open Solidworks and select a new part and also select the unit system mm. Moreover, all extrude are midplane extrude. (This is very important to maintain consistency in part and it will be useful while doing the assembly)

Part 1: Cam

The open new part, select front plan and select line to draw, now draw the line and constrained the sketch for the defined sketch as shown below;

Note: the dimensions of the cam will change as per the lift requirement as the objective of assignments to find the lift of cam, which I will highlight in motion study.

Once you drew this, exit the sketch and use extrude as shown below; save the part.

Part 2: Push Rod

Draw lines as shown below and give the constrains to fully define the sketch as shown, then exit the sketch and select revolve cut around the long vertical line and you will get the below results. Save the part.

Part 3: End Cap

Draw a sketch and give the fillets and also fully define the sketch as shown below;

And extrude the sketch, Save the part.

Part 4: Valve

Draw the sketch using the line as shown below and give the dimension and other constraints to fully define the sketch; after this exit the sketch and choose to revolve extrude option as shown below and save the part.

Part 5: Valve Mount

Draw a sketch using lines as shown below and give the dimension and other constraints to fully define the sketch, after this exit the sketch and do revolve extrude as shown below and save the part.

Part 6: Spring

We are not going to design spring, rather we will use the imaginary spring tension( as of real) in the motion study as we function to do so.

Assembly:

Go to new and select assembly and insert all the parts and use below mates;

Apart from this, we will use MOVE COMPONENT function under assembly to align the part as per the physical contact to make sure the physical touch and the precise place of the part for motion study. Please see the below screen short to understand.

And then save the assembly but before doing so just check all the parts are well constrained that is they are no moving in an unnecessary direction.

Motion Study:

Now go to SOLIDWORKS ADD ONs and select SOLIDWORKS MOTION

Now select the MOTION ANALYSIS for the motion study.

For all the motion study the contact will stay the same as shown below;

At last, the spring needs to assign as shown below by selecting the corner of the valve head and valve mount head as shown below;

Note: Time shown may vary for each study as I had to manually stop the simulation/motion study.

Speed and material will be the same for the tasks as shown below;

For high definition values &more accurate values we took 7200 frames per second with precise contact, this feature will help us to get a well-defined plot.

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." Some camshaft manufacturers list this value.

The camshaft "lift" is the resultant net rise of the valve from its seat. The farther the valve rises from its seat the more airflow can be provided, which is generally more beneficial. The greater lift has some limitations. Firstly, the lift is limited by the increased proximity of the valve head to the piston crown and secondly, greater effort is required to move the valve springs to a higher state of compression. The increased lift can also be limited by lobe clearance in the cylinder head casting. A higher valve lift can have the same effect as an increased duration where valve overlap is less desirable.

Cams that have excessive valve lift, running at high rpm, can cause what is called "valve float", where the valve spring tension is insufficient to keep the valve following the cam at its apex. This could also be a result of a very steep rise of the lobe, where the valve is effectively shot off the end of the cam rather than following the cams’ profile. This is typically what happens when a motor over revs. This is where the engine rpm exceeds the maximum design rpm. The valve train is typically the limiting factor in determining the maximum rpm the engine can maintain either for a prolonged period or temporarily. Sometimes an over-rev can cause engine failure when the valves become bent as a result of colliding with the piston crowns.

Design the lift;

Cam; Diameter_1 = 25mm, Diameter_2 = 10mm

Valve Lift

When talking about camshafts and lift, people usually mean a valve lift. This is the distance the valve actually moves. It is also called "gross lift." All camshaft manufacturers list this value.

1. Task: CAM Lift: 3.5 (mm); Speed: 1500 (RPM) Material: Cast Carbon Steel

For Cam Lift of 3.5mm;

Cam lift = ( L − R1 ) + R2

3.5 = ( L − 12.5 ) + 5

L = 11

Cam design for lift;

Save the changes in part and assembly. Now check the position of rocker and push rod along with cam as the dimension changes. If the physical contact is not happened then use the move component to do so.

Now run the simulation and generates the plot for the required condition as follows;

Plot:

• Valve Lift:

The plot is plotted with Linear Displacement (mm) against time as shown below.

As we can see in the plot, the linear displacement in mm and it goes from 5.05 till 5.275 at max and the displacement has increased over time, however, it will not cross the maximum limit as it will not be feasible then. The motion is indeed linear and steady.

Contact Forces:

• Cam and Push Rod;

The motion is smooth with some sudden rise in force for fraction of second, which I think may have happened because of increased in rotation and due to the non-symmetric edges of push rod contacting cam. Otherwise, if we see the motion of the valve it is very refined and it doesn’t show much impact of a sudden rise in forces as it is for a very small fraction of the second.

• Push Rob and Rocker Arm;

The motion is almost identical with cam & push rod contact force study with very minor changes, motion is smooth with some sudden rise in force for fraction of second, again which I think may have happened because of increased in rotation and due to the non-symmetric edges of push rod contacting cam. Otherwise, if we see the motion of the valve it is very refined and it doesn’t show much impact of a sudden rise in forces as it is for a very small fraction of the second.

• Rocker Arm and Valve (Magnitude);

For this motion study, we can see some major changes compared to above, the force is larger, and as I can understand it might be because of the change in mass and the surface in contact.

• Rocker Arm and Valve (Magnitude + X-direction);

Orange shows the study for X-direction and Blue shows the study for Magnitude, as we can see there is a huge difference in contact force and that is mainly because X-direction will show the forces in Horizontal direction which will sliding force and slippage (friction), whereas the magnitude will have accompanied the sum of forces acting due to the motion in contact with the 2 faces.

2. Task: CAM Lift: 6 (mm); Speed: 1500 (RPM) Material: Cast Carbon Steel

For Cam Lift of 3.5mm;

Cam lift = ( L − R1 ) + R2

6 = ( L − 12.5 ) + 5

L = 13.5

Cam design for lift;

Save the changes in part and assembly. Now check the position of rocker and push rod along with cam as the dimension changes. If the physical contact is not happened then use the move component to do so.

Now run the simulation and generates the plot for the required condition as follows;

Plot:

• Valve Lift:

The plot is plotted with Linear Displacement (mm) against time as shown below.

As we can see in the plot, the linear displacement in mm and it goes from 5.05 till 5.675 at max and the displacement has increased over time, however, it will not cross the maximum limit as it will not be feasible then. The motion is indeed linear and steady.

Contact Forces;

• Cam and Push Rod;

The motion is smooth with some sudden rise in force for fraction of second, which I think may have happened because of increased in rotation and due to the non-symmetric edges of push rod contacting cam. Otherwise, if we see the motion of the valve it is very refined and it doesn’t show much impact of a sudden rise in forces as it is for a very small fraction of the second. But if we observe the difference of lift in contact force, as the force is noticeably higher than task 1 and I think it might because of more time in contact.

• Push Rod and Rocker Arm

The motion is almost identical with cam & push rod contact force study with very minor changes (lower as compare to task 2-1^st study), motion is smooth with some sudden rise in force for fraction of second, again which I think may have happened because of increased in rotation and due to the non-symmetric edges of push rod contacting cam. Otherwise, if we see the motion of the valve it is very refined and it doesn’t show much impact of a sudden rise in forces as it is for a very small fraction of the second.

• Rocker Arm and Valve(Magnitude)

For this motion study, we can see some major changes compared to above, the force is larger, and as I can understand it might be because of the change in mass and the surface in contact. This time motion is very controlled yes the fraction rise in force is more times but overall it is better.

• Rocker Arm And Valve ( Magnitude v/s X-Direction)

Orange shows the study for X-direction and Blue shows the study for Magnitude, as we can see there is a difference but the not a huge difference as task 1 study and that is mainly because X-direction will show the forces in Horizontal direction which will sliding force and slippage (friction), whereas the magnitude will have accompanied the sum of forces acting due to the motion in contact with the 2 faces.

Result and Explanation:

As we can see the difference in the plot for the given 2 tasks, the cam lift of 6mm is somewhat better than the cam lift of 3.5mm. However, in some cases, a cam lift of 3.5 might be more useful than a 6mm lift. Again the lift of cam will proportionally affect the valve lift which the gross lift for the engine valve. The valve lift mainly examines for the intake ratio of fluid and if we want more fluid then can lift has to be more and vice versa.

Now for the contact forces, I think the lift will have a somewhat different effect on the contact force and also the pushrod (all parts) geometry will also affect on the contact force, if the sharp edge is in contact with any surface then it will have more contact force with sudden rise as we have seen in plots.

https://youtu.be/wn36NHaclLE

Errors or issues I faced:

Fortunately, none for the assignment.

Reference:

1. https://help.summitracing.com/app/answers/detail/a_id/4699/~/camshaft-lift#:~:text=When%20talking%20about%20camshafts%20and,base%20circle%20of%20the%20camshaft.
2. https://en.wikipedia.org/wiki/Camshaft