Mechanical Simulation
Technical Memo
912 North Main, Suite 210, Ann Arbor MI, 48104, USA
Phone: 734 668-2930 • Fax: 734 668-2877 • Email: info@carsim.com
www.carsim.com
CarSim 7.1 New Features and Bug Fixes
More Examples ...............................................................................................................1
Improvements in the Browser (CarSim.exe)...................................................................2
Management of Multiple CarSim Databases ........................................................2
Multiple Levels of Undo and Redo.......................................................................2
Road Segment Builder ..........................................................................................2
More Improvements ..............................................................................................2
Improvements in the Math Models .................................................................................3
Brakes with Boost and Thermal Effects................................................................3
TNO Delft-Tyre Model .........................................................................................3
Suspension Jounce and Rebound Stops ................................................................3
Parametric Trailer Hitch........................................................................................3
Improved Steering Geometry Calculations ...........................................................4
New Import Variables ...........................................................................................4
More VS Commands and Symbolic Functions.....................................................4
More VS API Functions........................................................................................5
Improvements in the Animator .......................................................................................5
Converting Files: Importing and Exporting ....................................................................5
Help and On-line Documentation ...................................................................................6
Bug Fixes and Errata.......................................................................................................6
Browser .................................................................................................................6
Math Models .........................................................................................................6
Example Database.................................................................................................6
CarSim 7.1 is a significant update that provides improvements in the existing browser and GUI, vehicle
models, simulation numerical methods, animator, and file import/export capabilities. There are also many
minor bug fixes and miscellaneous improvements. This technical memo highlights the improvements.
More Examples
Nearly all of the major new features are demonstrated in examples in the installed database to help you
learn to use them. The sidebars for most examples also contain notes describing interesting details of each
simulation.
In the installed example database in the category “*CS7.1 Extended Models” under the Datasets menu, a
simple steering controller has been implemented five different ways, using VehicleSim (VS) commands,
Visual Basic, MATLAB, and external C code. Two examples are provided using C: with and without
Simulink. In the same category, another example illustrates a sensor detecting a moving object shown by
the animator as a truck.
The category “*CS7.1 Simple ESC Controller” implements a simple Electronic Stability Control (ESC)
system in Simulink, and illustrates several tests involving this system.
June 28, 2007
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The category “*CS7.1 Measured Test Data” contains an example using SurfAnim, the CarSim animator,
to produce animations of data from a set of physical measurements that were imported using one of two
new file converter utilities.
The category “*CS7.1 Traffic Example” has two runs that show how traffic is added using VS commands
to define moving objects for the animator that are automatically positioned to stay within visual range (as
done in driving simulators and video games).
The category “*CS7.1 Generic Tables” has a run that simulates an extreme maneuver using a hand brake
with dynamics, using a new generic table that defines a nonlinear behavior with equations added at
runtime.
Improvements in the Browser (CarSim.exe)
Most CarSim users spend more time interacting with the CarSim GUI (the database browser) than any
other part of the software. This update includes some subtle but significant improvements.
Management of Multiple CarSim Databases
Perhaps the first thing you will notice when starting CarSim 7.1 is a window that lets you choose which
CarSim database will be used for the CarSim session. If there is only one database (a folder with the
default name CarSim_Data), the startup window can be disabled to eliminate this step in the launch
process. However, if you work with several databases, this greatly simplifies choosing which one to use.
If you choose an older version (CarSim 6.0x or 7.0x), CarSim 7.1 will offer to backup the old database
and update some files to convert to 7.1.
Multiple Levels of Undo and Redo
The functions of the Save and Undo buttons have been improved, and a Redo button has been added to
the browser toolbar. You can still force the current dataset to be saved at any time by clicking the Save
button. In addition, the new Undo button provides step-by-step undo of changes until the dataset returns
to the state it was in when the screen was entered. If you undo to a point where you forced a save by
clicking the Save button, you are prompted before the action is completed. If you undo by mistake, or just
to remember what a parameter was before you changed it, you can use the Redo button to restore your
change.
Road Segment Builder
A new browser library Road: Segment Builder was added to assist in creating road geometry from
scratch. Link to a Road: Segment Builder dataset from the Roads: 3D Surface screen to gain access to
this tool. Using it, you can specify straight and curved segments by length, number of degrees, number of
data points, and so on. You can specify cross-slope banking and transitions from banked to flat, and
generate tables of Z coordinates. The Segment Builder tool generates the tables used by the math models.
Several examples can be found in the installed example database in the category “*CS7.1 Road Segment
Builder” under the Datasets menu, and the on-line help for 3D Roads has been extended.
More Improvements
A browser library Generic VS Commands has been added for editing larger blocks of VS commands. It
can be linked from many other browser screens, helping you to make test procedures more portable.
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Screens were added as needed to support new model features. For example, six new screens were added
to support the extended brake model options.
Improvements in the Math Models
Brakes with Boost and Thermal Effects
This alternative to the original CarSim brake system model includes a description of the pedal and
linkage, a power assist booster with dynamic response, a more detailed model of the properties of each
brake with pressure/volume effects, hydraulic flow resistance, and thermal properties. A controller (such
as ABS) can be located optionally either upstream or downstream of the proportioning valves.
This brake model uses pedal force as an input control signal. The booster dynamics and hydraulic flow
properties include more effects important in the development of controller logic and in brake events with
rapidly changing apply pressures. The thermal effects allow fade to be simulated.
·
Six new libraries are added to the CarSim browser for the support of this model.
·
Several examples have been included showing the operation of this model. In the installed database,
the examples can be found in the category “*CS7.1 Advanced Brakes” under the Datasets menu
item.
TNO Delft-Tyre Model
The TNO Delft-Tyre 6.1 software is integrated with CarSim 7.1. The basic MF-Tyre runs with CarSim
with no additional license. The more detailed SWIFT Tyre with multiple contact points, rigid-ring
dynamics, and turn-slip is also supported for users who have purchased licenses from TNO.
User controls have been added to the Tire library screen for selecting among the Delft-Tyre options.
Several examples can be found in the categories “*CS7.1 Advanced Tires” and “*CS7.1 Tire Tester
(Delft Tire)” in the installed example database under the Datasets menu item. A chapter was added to the
on-line help file for Tires.
Suspension Jounce and Rebound Stops
In previous versions, suspension jounce and rebound stops were modeled as increases in stiffness of the
springs at the limits of travel. This method is convenient when suspension stiffness is measured at the
wheel spindle and included all the spring components. It is less convenient for situations when the jounce
and rebound stops or the springs needed to be changed individually. As an alternative, new non-linear
forces acting on the suspension have been provided to specify each component. Links for datasets
describing each part have been added to the Suspension: Compliance screens and the on-line help was
updated.
Parametric Trailer Hitch
For users with CarSim trailer licenses, an alternative method for specifying the properties of a trailer hitch
has been added. Instead of defining tables of each component moment, linear coefficients can be entered
for stiffness, total travel, and bump stop stiffness. The model also includes damping and hysteresis for the
hitch moments. A new library was added to the browser for this feature, and the documentation for
hitches was extended.
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Improved Steering Geometry Calculations
CarSim 7.1 adds further detail to the steering geometry improvements made in version 7.0. CarSim 7.0
introduced a true multibody steering geometry model, replacing the algebraic model of previous versions.
It captured the camber change, lateral load transfer, and migration of the center of tire contact effects that
were ignored in the algebraic model. It did not, however, capture the non-linear steering gain observed
when large caster and steering axis inclination angles are specified.
All of these effects are small for typical ranges of caster and steering axis (kingpin) inclination. For larger
angles, and at large steer angles, the non-linear gains become more apparent. The addition of these
features extends the range of vehicle specifications, maneuver types, and test objectives for which CarSim
is valid.
An option is provided on the Steering System library screen to specify whether steer angles are defined
at the ground, including the non-linear gain effects, or as rotation angles about the kingpin, ignoring them.
The first option is appropriate when steering geometry is measured with a Kinematics & Compliance test
rig with turntables at each wheel. The second option is useful if steer data is measured directly on a
running vehicle as rotation at the steering axis.
The steering system on-line help file is updated to include a discussion of these effects.
New Import Variables
About 60 new import variables are now supported to assist advanced users in extending the CarSim
models. Camber (IMP_CAM_CON_L1, L2, etc.) and its time derivative (IMP_DAM_CON_L1,
L2, etc.) can be used to extend or replace the internal definition of camber change. Output of the
steering
gear
(IMP_STEER_CON,
IMP_STEER_RACK_CON,
and
time
derivatives
IMP_DTEER_CON, and IMP_DTEER_RACK_CON) are useful for steer-by-wire and may other
applications. Systems like in-wheel motors for hybrid or electric vehicles can be modeled using moments
(IMP_MYUSM_L1, L2, etc.) applied to each wheel and reacted at the unsprung mass.
More VS Commands and Symbolic Functions
There are more options available for extending the CarSim math models using VS commands and
symbolic algebraic expressions. When introduced in 2007, the symbolic expressions supported standard
math functions (SIN, COS, MAX, etc.) and recognized all parameters, import variables, and output
variables from the math model. The VS functions also provided information about the 3D road geometry,
with functions such as ROAD_X, ROAD_Y, ROAD_YAW, etc.
CarSim 7.1 adds Boolean functions (AND, OR, NOT, etc.) to simplify equations involving multiple
conditions. It also adds ten new road access functions, to simplify the tracking of externally defined
objects that are common when developing scenarios for testing advanced warning and control systems.
(The new functions support the efficient tracking of 50 separate objects on the road.)
CarSim 7.1 also supports the use of table lookup functions in the symbolic expressions. For example, the
table that has target speed as a function of location on the road can be used for equations added with VS
commands. Most tables have gains and offsets that can now be set via VS commands. This lets advanced
users extend existing tables at runtime in order to provide extra sensitivity.
CarSim 7.1 includes a generic table with 12 datasets that exist solely for use within equations defined at
runtime. This allows you to take advantage of the CarSim database to define nonlinear relationships that
can be used in equations defined in VS commands, to define new controls within CarSim, or to export
information to external software such as Simulink. (An example is provided showing how the generic
table is used to implement an extreme maneuver using a parking brake: see “* CS 71 Generic Tables.”)
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13 new VS commands were added to help manage complicated scenarios, where equations and events are
added dynamically during a run. The new commands delete some or all of the equations or events in
various categories.
More VS API Functions
The VehicleSim application program interface (VS API) has been updated for convenient use in more
languages, and to provide consistent usage that is easily updated as new features appear in products.
Examples are now provided for MATLAB and Visual Basic (VB), along with documentation in the VS
API manual and in a tech memo that implements a simple steering controller using VS commands,
MATLAB, VB, and C.
All of the functions that can be used in equations added at runtime with VS commands have also been
added to the API, including the new road functions that can track 50 moving objects.
Access to the internal variables in the VS solver program has been improved, to include access to the
offsets and gains associated with the tables.
More internal functions have been added to the API in support of advanced users; a CarSim 7.1 VS solver
DLL has 75 API functions. For example, new functions are provided to support the combination of model
extensions in C that also work when the DLL is used with Simulink.
Improvements in the Animator
The animator has been modified to improve performance and add features. Here are some of the major
changes.
·
The internal processes were revised to make better use of graphics card hardware and use almost no
CPU time. This supports multiple instances of the animator running simultaneously.
·
The number of “ghost” images was increased to 1000, to allow visualization of tire paths.
·
The visibility of images was made continuous, allowing variable transparency. This has been used
to visualize skid marks, where the visibility of the path is proportional to “skidding.”
·
Camera settings have been added to automatically track a target (such as a vehicle) from a fixed
camera position, and automatically zoom to hold the target in the frame. This simulates a human
camera operator at a racetrack or proving ground.
·
“Audio zoom” is supported, to automatically adjust the sound level based on distance from the
camera.
Converting Files: Importing and Exporting
The CarSim animator and plotter shows data that is contained in pairs of files with extensions ERD and
BIN, often called ERD files. A utility program in CarSim has automatically converted ERD files to other
formats for export to other software, such as spreadsheets and MATLAB. The converter has been
extended to also convert data from spreadsheets to ERD files, to simplify the process of importing data
into CarSim for viewing with the animator and plotter. In addition, a simple utility program is installed
for drag-and-drop conversion of CSV (comma-separated variable) files from spreadsheets to ERD files
for animation.
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Help and On-line Documentation
The “Help” documentation has been reorganized. It has been broken into a larger number of smaller
sections, making it easier to find the subject you are looking for.
All of the reference manuals have been updated for the CarSim 7.1 release.
New text and spreadsheet documentation files are installed for the new models in the
CarSim_Prog\Programs\Solvers\Readme folder.
Existing technical memos have been updated and in some cases extended. New technical memos have
also been added to describe how to do specialized tasks in CarSim. All of the documentation is now
directly accessible from the Help menu of the CarSim database browser.
Bug Fixes and Errata
Browser
·
On the Batch Runs screen, the function of the Miscellaneous Yellow Field and Overriding Data
Link were corrected. Previously, these settings were ignored during the batch run.
·
A bug on the Events and Procedures screen, when linking to another Events and Procedures
dataset from one of the miscellaneous data links could cause datasets to be written incorrectly. It
has been corrected.
·
All other known browser bugs have been corrected. Review the Users area on the CarSim.com
website for details.
Math Models
·
A bug was corrected in the AB-2 integration routine. The version 7.01 AB-2 produced incorrect
results, and users were advised not to use the AB-2 option. The AB-2 integrator now functions
correctly. See the Solver Programs Reference Manual for Details.
·
A bug in the math models caused the reaction to brake moments on independent suspensions to be
ignored. This has been corrected. Anti-dive geometry effects will now be completely captured.
·
The values of Mz (the total moment about the unsprung mass Z-axis) applied to suspension
compliances (steer vs Mz and inclination vs Mz) were incorrect in version 7.0 and 7.01. In general,
calculated compliance effects involving Mz were much smaller than they should have been,
because the magnitude of the internal representation of one of the component moments was always
1.0, and the sign was always positive. This error has been corrected, and the correct values of Mz
are now applied to the compliances.
Example Database
·
Datasets for the Aerodynamic Yaw Moment in earlier releases included values not generally
representative of passenger cars. As they were originally released, they implied aerodynamic
centers of pressure farther forward than would ordinarily be expected. The effect on vehicle
performance was generally small. These datasets were replaced with improved data for the release.
The individual datasets have names different from those in earlier version, but example runs and
vehicles that use them have the same names as previously released.
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·
Datasets for the Suspension: Dive Angle (Caster Change) screen in earlier releases included data
not generally representative of passenger cars. As they were originally released, they implied “prodive” suspension geometry. The effect on vehicle performance was generally small. These datasets
were replaced with improved data for the release. The individual datasets have names different
from those in earlier, but example runs and vehicles that use them have the same names as
previously released.
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