© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community 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.
Dynamic Simulation : Cam Example Problem
Feb 23, 2016
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. - PowerPoint PPT Presentation
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© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity
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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.
© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity
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System
A cross section of the valve train components is shown in the figure.
The valve guide, lower spring plate, and valve guide seal are stationary.
The keepers, upper spring plate, cap, and tappet move as one assembly.
There is relative motion along the axis of the valve stem as the cam rotates and compresses the valve spring.
cam
tappetcap
upper spring plate
valve spring
valve guide
valve
valve guide seal
Keepers (keys)
lower spring plate
Section 4 – Dynamic Simulation
Module 8 – Cam Example Problem
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Cylinder Block
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.
This part is grounded.
Cylinder block
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Module 8 – Cam Example Problem
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Cam Bearing
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.
cambearing
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Module 8 – Cam Example Problem
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Assembly Constraints
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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Module 8 – Cam Example Problem
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Valve Spring
The valve spring has the following properties. Stiffness 15 N/mm Free length 40 mm Wire diameter 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.
Section 4 – Dynamic Simulation
Module 8 – Cam Example Problem
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Dynamic Simulation Environment
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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Module 8 – Cam Example Problem
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Ground Constraints
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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Mobile Groups
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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Module 8 – Cam Example Problem
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HighlightedMobile Groups
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Standard Joints
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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Standard Joints
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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Module 8 – Cam Example Problem
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Gravity
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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Module 8 – Cam Example Problem
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Valve Spring
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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Valve Spring
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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Module 8 – Cam Example Problem
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Valve Spring
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.
Note also that a Force Joints line is created in the browser.
Spring
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Module 8 – Cam Example Problem
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Valve Spring
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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Module 8 – Cam Example Problem
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Cam & Follower Contact
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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Module 8 – Cam Example Problem
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Cam & Follower ContactSection 4 – Dynamic Simulation
Module 8 – Cam Example Problem
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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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Cam Shaft Rotational Motion
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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Module 8 – Cam Example Problem
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Motion Constraint
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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Module 8 – Cam Example Problem
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Simulation Player Settings
The simulation will be set to complete three revolutions.
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.
Click to perform simulation
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Module 8 – Cam Example Problem
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Output Grapher
The output grapher is used to plot the computed results.
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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The spring force is selected.
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Output Grapher
Multiple traces may be displayed at the same time.
3D Contact Force
Spring Force
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Module 8 – Cam Example Problem
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Float
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 pre-load or increasing the cam rotational speed.
Section 4 – Dynamic Simulation
Module 8 – Cam Example Problem
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Module Summary
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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Module 8 – Cam Example Problem
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