Dynamic Simulation:
Cam Example Problem
Objective



The objective of this module is to show how to add force joints to a
model using the Dynamic Simulation environment in Autodesk
Inventor software.
The specific example problem involves determining forces in various
components of a boxer engine intake valve assembly, including
springs, dampers and various types of contacts.
The Dynamic Simulation environment implements the theory covered
in preceding modules.
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Section 4 – Dynamic Simulation
System
Module 8 – Cam Example Problem
Page 2
A cross section of the valve train
cam
components is shown in the figure.
 The valve guide, lower spring
tappet
plate, and valve guide seal are
Keepers (keys)
stationary.
valve spring
 The keepers, upper spring plate,
valve guide
cap, and tappet move as one
seal
assembly.
 There is relative motion along the
valve
axis of the valve stem as the cam
rotates and compresses the valve
spring.

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cap
upper spring
plate
lower spring
plate
valve
guide
Education Community
Section 4 – Dynamic Simulation
Cylinder Block
Module 8 – Cam Example Problem
Page 3

An artificial part
(cylinder block) is
created to simulate the
cylinder head.

This part provides a flat
surface for the lower
spring plate to rest on
and a cylindrical hole for
the valve guide.

Cylinder block
This part is grounded.
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Section 4 – Dynamic Simulation
Cam Bearing
Module 8 – Cam Example Problem
Page 4

Another artificial part is
created to provide a fixed
axis for the cam to rotate
about.

This part is called the cam
bearing.

The cam bearing is
grounded.
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cam
bearing
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Section 4 – Dynamic Simulation
Assembly Constraints
Module 8 – Cam Example Problem
Page 5

Inserts and mates are used to
create positional constraints
between the parts.

The grounded parts (cylinder
block and cam bearing) provide
fixed axes and surfaces that
serve as starting points.

For example, a centerline mate
exists between the valve and
the valve guide.
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Section 4 – Dynamic Simulation
Valve Spring
Module 8 – Cam Example Problem
Page 6

The valve spring has the following
properties.



Stiffness
Free length
Wire diameter
15 N/mm
40 mm
4 mm

The valve spring visibility is
suppressed in the Assembly
environment prior to going to the
Dynamic Simulation environment.

The spring will be added as a force
joint in Dynamic Simulation.
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Section 4 – Dynamic Simulation
Dynamic Simulation Environment
Module 8 – Cam Example Problem
Page 7
The Dynamic Simulation
environment in Autodesk Inventor
software is entered by selecting the
Dynamic Simulation icon that is seen
when the Environments tab is
selected.
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Section 4 – Dynamic Simulation
Ground Constraints
Module 8 – Cam Example Problem
Page 8
The information shown on the right is
automatically created upon entering
Dynamic Simulation.
 Note that the Cam Bearing, Cylinder
Block, suppressed valve spring, and
Welded Group 1 are grounded.
 Welded Group 1 consists of the valve
guide, valve guide seal, and lower
spring plate.

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Section 4 – Dynamic Simulation
Mobile Groups
Module 8 – Cam Example Problem
Page 9

There are two Mobile Groups:
Welded Group 2 contains the
intake valve, upper spring plate,
tappet, keepers (valve keys),
and cap.
 The second mobile group is the
Intake Cam.


The Mobile Groups can be
highlighted by right clicking on
Mobile Groups in the browser
and selecting Color Mobile
Groups.
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Highlighted
Mobile Groups
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Section 4 – Dynamic Simulation
Standard Joints
Module 8 – Cam Example Problem
Page 10
Two standard joints were
automatically generated.
 The first is a Revolution Joint
that allows rotational motion
about the cam shaft and cam
bearing common axis.
 The common axis is denoted
by the arrow with three
heads.

Each part has a joint coordinate system. The green coordinate system is associated
with the cam and the blue is associated with the bearing. The x-axis has a single
arrow head, the y-axis has two arrow heads, and the z-axis has three arrow heads.
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Section 4 – Dynamic Simulation
Standard Joints
Module 8 – Cam Example Problem
Page 11
The second standard joint is a
cylindrical joint between the
second welded group and the
first welded group.
 The second welded group
contains the valve and the parts
that move with it.
 A cylindrical joint allows
translation and rotation about a
common axis.
 Note that the z-axis for both
joint coordinate systems are
aligned in the figure.

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Section 4 – Dynamic Simulation
Gravity
Module 8 – Cam Example Problem
Page 12

The direction and magnitude of
gravity is set by double clicking on
the gravity icon in the browser and
selecting Vector Components.

In this problem gravity is acting in
the negative-y direction.

An arrow indicating the direction
will be displayed on the screen.
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Section 4 – Dynamic Simulation
Valve Spring
Module 8 – Cam Example Problem
Page 13

The valve spring is added as a
Spring/Damper/Jack joint.

This option is found by right
clicking on Standard Joints in
the browser and selecting
Spring/Damper/Jack.
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Section 4 – Dynamic Simulation
Valve Spring
Module 8 – Cam Example Problem
Page 14
A spring is created between the
lower spring plate (Point 1) and
the upper spring plate (Point 2).
 A joint coordinate system is
displayed for both parts with its
origin at the points selected.
 The z-axes for both coordinate
systems are automatically
oriented along the axis of the
valve.
 This is the only direction that
the spring retainers can move
in.

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Section 4 – Dynamic Simulation
Valve Spring
Module 8 – Cam Example Problem
Page 15

After selecting ok, the spring
shown in the figure is created.

It does not have the correct
geometry nor does it have the
correct stiffness.

Spring
Note also that a Force Joints
line is created in the browser.
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Section 4 – Dynamic Simulation
Valve Spring
Module 8 – Cam Example Problem
Page 16

The correct spring geometry
and stiffness is entered by
right clicking on the
Spring/Damper/Jack joint and
editing the properties
information.

Notice that the spring
geometry now has a realistic
appearance.
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Section 4 – Dynamic Simulation
Cam & Follower Contact
Module 8 – Cam Example Problem
Page 17

A 3D Contact joint is used to
define the contact between the
cam and cam follower.

This joint type is found by
selecting the Standard Joints
line in the browser, right
clicking and selecting Add a
Joint.
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Section 4 – Dynamic Simulation
Cam & Follower Contact
Module 8 – Cam Example Problem
Page 18
 The top surface of the tappet is
selected for Component 1.
 The cam dwell surface is selected
for Component 2.
 Autodesk Inventor’s Dynamic
Simulation knows that the
contiguous lobe surface is part of
Component 2.
 A 3D contact joint is added to the
Force Joint group in the Browser.
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Section 4 – Dynamic Simulation
Cam Shaft Rotational Motion
Module 8 – Cam Example Problem
Page 19

A performance boxer style engine is capable of crank shaft rotation
speeds of 7,000 rpm.

The intake and exhaust cams will rotate at ½ of the crank speed or
3,500 rpm.

This converts to a cam shaft speed of 21,000 deg/sec.

Deg/sec are units needed on the next slide to define the motion.
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Section 4 – Dynamic Simulation
Motion Constraint
Module 8 – Cam Example Problem
Page 20
Motion is applied by
editing the properties of
the Revolution Joint
between the cam bearing
and cam shaft.
The motion is applied to
the rotational DOF.
Click the “Enable imposed
motion box” to allow the
velocity to be set.
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Section 4 – Dynamic Simulation
Simulation Player Settings
Module 8 – Cam Example Problem
Page 21

The simulation will be set to
complete three revolutions.
Click to perform simulation

At 21,000 deg/sec it will take
0.0171 seconds to complete a
revolution or 0.051 seconds for
three revolutions.

Solution data will be captured at
each degree of rotation or 360 times
per second.

This results in 1080 capture points.
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Section 4 – Dynamic Simulation
Output Grapher
Module 8 – Cam Example Problem
Page 22
The output grapher is used to plot the computed results.
The spring
force is
selected.
Flat portion is the spring
force during dwell. The
negative value is due to
the spring pre-load that is
controlled by the spring’s
free length.
The spikes are due to
the cam lobe
depressing the spring.
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Section 4 – Dynamic Simulation
Output Grapher
Module 8 – Cam Example Problem
Page 23
Multiple traces may be displayed at the same time.
3D Contact Force
Spring Force
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Section 4 – Dynamic Simulation
Float
Module 8 – Cam Example Problem
Page 24

Float is realized when there is
insufficient spring stiffness
and/or pre-load to keep the
cam and cam follower in
contact.

Cam float can be seen in this
problem by decreasing the
spring constant to 3 N/m.

Cam float can also be affected
by decreasing the spring preload or increasing the cam
rotational speed.
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Section 4 – Dynamic Simulation
Module Summary
Module 8 – Cam Example Problem
Page 25

In Module 6 of this section, the theory by which multi-body dynamic
programs compute the forces acting between the bodies was
presented.

This module provided an example of how to set-up and run a
problem that computes forces in Autodesk Inventor’s Dynamic
Simulation environment.

Assembly constraints were automatically converted to kinematic
constraints while moving from the Assembly and Dynamic Simulation
environments.

Additional constraints were implemented within the Dynamic
Simulation environment.
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