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    vzwickSchreibmaschinentextSIMULATION AND CALCULATION VEHICLE DYNAMICS

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    vzwickSchreibmaschinentextSafe and comfortable vehicle handling is taken for granted today. The variety of different versions is increasing, active systems have to be controlled, and complex electronics must be mastered. This is possible only with the application of vehicle dynamics simulation.Today, OEMs have access to a wide range of freely available products for vehicledynamics simulation, and more and more suppliers are entering the market.TESIS DYNAware explains the main criterias for application oriented solutions.

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    vzwickSchreibmaschinentextTHE CHALLENGE OF VEHICLE DYNAMICS SIMULATION A CRITICAL ASSESSMENT

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  • AUTHOR

    Dr. Cornlius Chucholowski General Manager of TESIS DYNAware

    GmbH

    Understanding Dynamic

    Simulation

    Dynamic simulation is the numerical

    integration of differential equations

    that describe system behavior.

    Rapid progress in computer tech-

    nology now makes it easier to apply

    this demanding and time-consuming

    computing process in small time

    steps to increasingly complex

    systems. The tools have also

    fundamentally changed. Whereas

    the differential equations used to be

    created and programmed manually,

    we now have special tools for multi-

    body systems or generic modeling

    programs that can be applied

    without the need for mathematical

    knowledge. What is more, there are

    now ready-made libraries for

    increasing numbers of sub-systems

    that users can employ.

    User-friendly complete solutions for

    vehicle-dynamics simulation support

    first-time users and quickly lead to

    results. However, this simplicity of

    use also has a disadvantage.

    Users no longer need to deal with

    the funda-mental principles and to

    critically query the results. Experts

    know that there is never one exact

    solution, but only an approach to-

    wards reality. The result can only be

    as exact as the modeling process

    and the numerical data permit.

    Furthermore, even the best program

    is useless if there are no valid data

    available for parameterization.

    Simulation is an indispensable tool

    for the validation of vehicle dy-

    namics and active control systems.

    However, users must be aware of

    the background conditions and must

    select the properly adapted tools

    and modeling depths. It also goes

    without saying that simulation will

    not achieve its full benefits unless it

    is supported by road tests .

    Demands on Vehicle Dynamics

    Simulation

    The experience of TESIS

    DYNAware goes back to a time in

    which there were no or only very

    few tools for dynamic simulation

    and every program had to be

    created individually.

    Simulation enables trustworthy

    predictions to be made, provided

    that the user is clear about its

    limitations. One danger is to have

    blind faith in numerical data.

    The integration process and the

    computing step size should be

    selected in adaptation to the

    problem. The computing step size

    is oriented towards the dynamics of

    the system and must be small

    enough to resolve high-frequency

    vibrations. A computing step size

    that is too small will result in

    "numerical noise" and will falsify the

    result. TESIS DYNAware is

    specialized in real-time-capable

    simulation, as is required for testing

    ECUs in HiL operation. In real-time

    operation, events for example for

    a control mode changeover for the

    transition from grip to skid must

    be given special treatment in order

    to achieve precise results even with

    a fixed step size. This is not covered

    by standard libraries. Very large

    libraries tempt users to make the

    models more detailed than necessa-

    ry. Detailed models require high

    computing power and are more

    complex to parameterize and

    validate. An increase in the number

    of parameters also increases the

    susceptibility to errors.

    For proof of concept tests, it is also

    advisable to make use of very

    simple models, such as a point

    mass model for driving performance

    and fuel consumption, a single-track

    model for lateral dynamics or a

    quarter-vehicle model for vertical

    dynamics. These models make it

    possible to perform an analytical

    study that is well suited for

    determining control structures and

    testing control concepts, but is less

    suitable for applying parameters.

    Conventional chassis development

    uses simulations based on generic

    multi-body programs, such as

    ADAMS/Car.

    The high-fidelity applications can

    also consider flexible structures.

    The models are derived from

    component and design data.

    Dynamic truck tipping test: Comparison of simualtion and test drive in the animation

    TESIS DYNAware Suspension Analysis Toolbox enables the determination of axle kinematic and axle compliance from virtual or real K&C test rig measurements.

  • Vehicle manufacturers go to great

    lengths to parameterize the complex

    models and to validate them to such

    an extent that they can be used as

    virtual reference vehicles. Suppliers

    seldom have access to the data

    required or cannot afford the effort

    involved.

    The high-fidelity models are focused

    on new designs. For functional

    development and the testing of

    control systems, active systems, and

    ECUs, specialized vehicle dynamics

    programs are used that are easy to

    parameterize and which can also

    run in real time on HiL systems.

    The depth of detail is reduced, but is

    still fine enough to simulate the most

    important vehicle-dynamics effects.

    Up to 30 Hz, the results hardly differ

    from those of high-fidelity programs.

    The TESIS DYNAware programs

    use Simulink as the runtime environ-

    ment. Simulink is a preferred

    platform for developing control

    systems from their initial design to

    their series production maturity. As an alternative to resolved axle

    modeling, users can specify

    kinematics maps with compliance,

    which they calculate on the real ve-

    hicle or by analyses on the complex

    full vehicle model. The concept

    developed by TESIS DYNAware has

    proven itself extremely well and is

    used by suppliers who do not have

    any design data at their disposal

    Full Vehicle Toolkit

    3D vehicle dynamics includes

    lateral, longitudinal, and vertical

    dynamics. The three areas are

    strongly interwoven.

    The distribution of driving and

    braking torque to the front and rear

    axle changes the self-steering

    behaviour. In an electric or hybrid

    vehicle with selective drive to each

    axle, this has an impact on energy

    management. Roll stabilization

    systems or active suspensions also

    have an influence not only on