Motion_Sim_and_FEA

Motion Simulation and FEA
Benjamin Labrosse
BSc (Hons) Automotive Engineering
January 9, 2015

In the automotive world it is beneﬁcial to understand the forces experienced by valves
in an engine. If a valve experiences too little stress it is considered to be over engineered
and be too heavy, reducing the potential performance of the engine. On the other hand,
if a valve experiences too large a stress the valve could bend excessively and fracture,
potentially causing damage to the engine. This leads to the aim of this paper where a
valvetrain has been measured and modelled in a CAD package and analysed through
FEA. The valve was modiﬁed according to the results of the FEA process to potentially
increase the performance of the engine.

Contents
1. Introduction 5
2. Methodology 6
2.1. Motion simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. FEA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Analysis 10
3.1. Valve stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2. Valve displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3. Valve rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.4. Valve reaction force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4. Modiﬁcations to improve the valve design 13
4.1. Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2. Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5. Conclusion 17
A. Figures for the FEA and motion simulation processes 19
3

List of Figures
2.0.1.The links and joints in the valvetrain model . . . . . . . . . . . . . . . . 6
2.0.2.Results of the spring dyno test . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.3.Degrees of freedom of a body, [Wang and Clarke, n,d] . . . . . . . . . . . 8
3.1.1.The maximum stress experienced by the valve . . . . . . . . . . . . . . . 10
3.1.2.The maximum stress experienced by the valve from a side view . . . . . . 11
3.2.3.The displacement of the valve under stress . . . . . . . . . . . . . . . . . 12
4.1.1.Maximum stress experienced by the valve . . . . . . . . . . . . . . . . . . 13
4.1.2.Second view of the maximum stress experienced by the valve . . . . . . . 14
4.1.3.The nodal displacement of the redesigned valve . . . . . . . . . . . . . . 14
4.2.4.The stress experienced by a titanium alloy valve . . . . . . . . . . . . . . 15
4.2.5.Nodal displacement of a titanium valve . . . . . . . . . . . . . . . . . . . 16
A.0.1.Applying a material property to the valve . . . . . . . . . . . . . . . . . 19
A.0.2.Applying a mesh collector . . . . . . . . . . . . . . . . . . . . . . . . . . 20
A.0.3.The application of the 3D Tetrahedral mesh . . . . . . . . . . . . . . . . 20
A.0.4.The mesh applied to the valve . . . . . . . . . . . . . . . . . . . . . . . . 21
A.0.5.The eﬀect of the nodes on the valve . . . . . . . . . . . . . . . . . . . . . 21
4

1. Introduction
Computer Aided Design (CAD) and Finite Element Analysis (FEA) play major roles in
the design of new components or the analysis of already existing components. Through
the use of these tools, an engineer can conclude whether a component is overly engi-
neered, that is, has been made with too much material or under engineered where a
component can be seen to fail. In both instances, the engineer can make modifications
to the component without making prototypes and completing live testing. This leads to
a reduced long term cost to the company in terms of finance and time.
The aim of this assignment is to measure and weigh real components from a system,
such as a valvetrain or suspension assembly, and create a CAD model of this system.
A motion simulation of this CAD model will be created and then a singular component
from the model will be put through an FEA. This will allow the author to modify the
CAD model as they believe fit, for example, modifying the dimensions of the component
in the model if too little or too much strain can be seen. The author has come to a
decision to model a valvetrain, consisting of a camshaft, bucket, collets, valve, spring,
spring retainer and a valve seat signifying the head of the engine. The CAD package
being used is Siemens NX8.5, created and sold by Siemens.
5

2. Methodology
The initial step to completing the aims of this assignment was to measure and weigh
the system chosen. The valvetrain components were measured using a vernier caliper
and weighed using scales. As there are small components in a valvetrain, high accuracy
low weight scales were used to measure the smaller components. Once the dimensions
of the valvetrain were obtained, the CAD model was created and assembled.
Figure 2.0.1.: The links and joints in the valvetrain model
As all parts were obtained from a matching head, the correct spring was available.
The spring was placed in the spring dyno to obtain the spring rate. A graph was made
showing the results from the test, see Figure 2.0.2. The spring rate was obtained from
the gradient of the graph and came out to be 13.13898N/mm.
The use of a vernier caliper is acceptable in the measurement of the majority of the
parts although this method is not suited to the measurement of the lobes. Had the
author known at the time, the measurement of the lobe would have been done by using
DTI gauges to get accurate measurements of the slope of the lobe. Using a vernier
caliper does not provide a true representation of the lobe proﬁle. This unrealistic lobe
6

Figure 2.0.2.: Results of the spring dyno test
profile does not allow the bucket to follow the lube therefore creating a phenomenon
called valve jump. This will lead to inaccuracies in the motion simulation but may not
effect the FEA results.
2.1. Motion simulation
The motion simulation was then completed by applying joints and links to the model,
seen in Figure 2.0.1. Links are used to group separate components that move together,
for example, in a valvetrain the collets, spring retainer, valve and spring all move together
when the camshaft pushes the bucket down. Joints are applied to the links to remove
the degrees of freedom (DOM) of the links therefore acting as constraints in the system.
Links are defined as a “rigid body with at least two points for attaching other links
(nodes)” and joints as a “connection between at least two links” by [Howe, 2006]. When
the motion simulation process commences, each component has six degrees of freedom.
The degrees of freedom in a model signify the parameters in which a body can move.
The body can move translationally in the planes x, y and z and rotationally in a, b and
g shown in Figure 2.1.3. In NX8.5, the degrees of freedom are denoted by the Grübler
count.
Table 2.1.1 shows the links created as well as the joints applied. Each joint has a base
link, the base link is the one about which each joint moves. In this case, the base link
of the revolute and slider joints is the valve seat as they move about the valve seat.
7

Figure 2.1.3.: Degrees of freedom of a body, [Wang and Clarke, n,d]
Link Joints Reasoning
Cam Revolute The revolute joint allows the cam to
revolve and a driver was applied to it
Bucket/spring
retainer/collets/valve
Slider The slider joint allows a link to move
in one plane
Valve seat Fixed A fixed joint fixes the selected link in
space
Table 2.1.1.: The links and joints in the model
2.2. FEA
Material properties
The initial step to creating an FEA model is to apply material properties to the com-
ponents being analysed. In this case it is simple as there is only one component being
analysed meaning that only one material is present. As it is unknown what engine this
valvetrain has originated from, it has been assumed that the valve has been made from
4340 steel. Figure A.0.1 shows the window in which the user applies a material property.
Application of a mesh
The forces generated are applied to the mesh on the valve. Meshes are made up of nodes
and elements. The elements are the triangles visualized on screen and can be seen in
Figure A.0.4.
The first step to applying a mesh is to create a mesh collector. The mesh collector
8

allows the user to apply different meshes to different materials. As there is only one
material in this FEA only one mesh collector needs to be added. The window used to
create a mesh collector is shown in Figure A.0.2.
The mesh is applied by selecting the 3D Tetrahedral mesh function. This applies a
mesh with elements taking the form of triangles. When creating a 3D mesh the user
must define in which mesh collector the mesh will be added. The element size must also
be selected. Element size varies depending on the parameters desired which is chosen by
the use of the component. Larger components typically have a larger elements, although
zones of smaller elements can be applied to more force sensitive areas. Siemens NX8.5
has a capability to automatically choose the element size which is derived from the area
of the component. The window for mesh creation is shown in Figure A.0.3 and shows
the desired mesh collector and element size which has been denoted automatically by
the software.
Once a mesh has been created, it will appear on screen as seen in Figure A.0.4. From
here, the load transfer data of the valve can be imported from the values obtained
previously in the spreadsheet.
Generation of nodes
After importing the load transfer of the valve, NX8.5 will generate two nodes in the
positions from which the forces are experienced. In this case, a node at the top of the
valve and at the bottom of the valve were generated. From the nodes, the user must
input the type of force being applied as well as the surfaces on which they are acting. The
surfaces on which the forces are applied at the top of the valve is shown in Figure A.0.5.
9

3. Analysis
CAD packages are made to visually exaggerate the eﬀects of the forces produced in FEA.
As such, results obtained appear to show a greatly deformed valve but upon examination
are not very signiﬁcant. The analysis has been completed assuming a cam speed of
4500RPM, meaning that the crank would be revolving at 9000RPM. This exceeds the
engine speed of the majority of road cars so knowing that the valve can tolerate this
speed ensures that the valve will not break under any speed.
3.1. Valve stress
The package has shown that the valve experiences a maximum force of 255.11N/mm2
. It
has been assumed that the valve is made of 4340 Alloy Steel. According to [AZO Mate-
rials, 2012], 4340 steel has a yield strength of 470MPa which is converted to 470N/mm2
.
The yield strength is the point at which the object begins to deform permanently. The
valve is therefore able to tolerate approximately twice that it is currently experiencing.
Figure 3.1.1.: The maximum stress experienced by the valve
10

The bending that is experienced is seen near the bottom of the valve on the outer
extremity of the shaft, see Figure 3.1.2. The maximum stress is seen at this point as the
valve is bending at this point.
Figure 3.1.2.: The maximum stress experienced by the valve from a side view
3.2. Valve displacement
The valve experiences maximum bending when the maximum stress is seen. The max-
imum displacement is seen to be at the top of the valve where the collets sit meaning
that the tip of the valve is being bent away from the center line. This bending has a
maximum magnitude of 0.446mm. The tolerance of valves in the engine that this valve
originates is unknown but the author assumes that a valve has a larger tolerance to ﬂoat.
This means that the valve would be able to bend more.
3.3. Valve rotation
The software provides information on the rotation of objects being FEA’d. This feature
is useful in components such as driveshafts as they are twisted under force. A valve
doesn’t rotate so the system has given a maximum angle of 0°.
11

Figure 3.2.3.: The displacement of the valve under stress
3.4. Valve reaction force
The package has given a result for the reaction force on the valve as 5 × 10−10
N which
is negligible and can be ignored when designing the valve.
12

4. Modiﬁcations to improve the valve
design
4.1. Dimensions
In order to improve the valve, the author has decided to decrease the diameter of the
valve shank. The top of the valve has remained unmodiﬁed so that the interaction
between the bucket and the valve is unaltered. This reduces the weight of the valve
which means that the engine designer can include lighter springs in the valvetrain which
further reduces the weight. Reduced weight can increase the performance of the engine
as the valve is opened more quickly. A quicker opening of the valve will mean that the
Figure 4.1.1.: Maximum stress experienced by the valve
valve will be open longer than the original valve. This would allow more air/fuel to
be added to the cylinder. Less wear will be experienced so the longevity of the engine
will be increased as well as the performance. The increased longevity will reduce the
quantity of valves needed over the life cycle of the engine so less resources are needed.
13

As predicted, the thinner shank has increased the stress experienced by the valve to
248MPa, see Figures 4.1.1 and 4.1.2. This stress remains within the tolerance of the
material, see Section 3.1, so the modiﬁcation is acceptable.
Figure 4.1.2.: Second view of the maximum stress experienced by the valve
The maximum displacement of the nodes seen is 0.5mm which appears to be acceptable
as the tolerance of ﬂoat of the valve in the head is larger than 0.5mm. This can be seen
in Figure 4.1.3.
Figure 4.1.3.: The nodal displacement of the redesigned valve
14

Figure 4.2.4.: The stress experienced by a titanium alloy valve
4.2. Material
The author decided to make another modification to the original valve. The material
was changed from 4340 steel to a titanium alloy. Titanium is a lighter material than
steel and has a tensile strength of 880MPa, [Aerospace Specification Metals, Inc., n,d],
compared to 470MPa of 4340 steel. This means that the valve could be made thinner
than a steel valve and would have similar benefits to reducing the diameter of the valve.
Titanium is more expensive than steel however so is not usually used in road vehicles.
The titanium valve experiences the same maximum stress as a steel valve but a larger
bending is seen, see Figure 4.2.5. A nodal displacement increase of 0.3mm is seen so the
change of material is not beneficial in this application.
15

Figure 4.2.5.: Nodal displacement of a titanium valve
16

5. Conclusion
The aim of this assignment was to measure, model and FEA an existing system with
moving parts. The second aim was to then modify the component that was FEA’d to
improve it. A valvetrain has been modelled and the valve FEA’d. The valve was then
modified by changing the diameter of the valve shank and by changing the material of
the valve. The change in dimensions brought about that experienced a larger stress
but was within the capabilities of the material. The greater stress would increase the
performance of the engine without sacrificing the integrity of the valve. The change in
material provided conflicting results. Titanium has a greater yield strength according
to the FEA performed less favourably than steel as a greater bending is experienced by
a valve made of titanium than one made of steel.
17

References
Aerospace Speciﬁcation Metals, Inc. Titanium ti-6al-4v (grade 5), annealed, n,d. URL
http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MTP641.
AZO Materials. Aisi 4340 alloy steel (uns g43400), September 2012. URL http://www.
azom.com/article.aspx?ArticleID=6772#3.
Robert Howe. Linkages engineering sciences 51, 2006. URL http://isites.harvard.
edu/fs/docs/icb.topic192304.files/lectures/ES51-Lecture-34-04-links-1.
pdf.
Dr. X Wang and Dr. T A Clarke. Determination of the six dof parameters of cad-based
objects. Technical report, City University London, n,d.
18

A. Figures for the FEA and motion
simulation processes
Figure A.0.1.: Applying a material property to the valve
19

Figure A.0.2.: Applying a mesh collector
Figure A.0.3.: The application of the 3D Tetrahedral mesh
20

Figure A.0.4.: The mesh applied to the valve
Figure A.0.5.: The eﬀect of the nodes on the valve
21

Motion_Sim_and_FEA

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