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Vehicle Dynamics Simulation (VDS)


VDS Tour: SPECIAL FEATURES

VDS contains the same core vehicle model as MRA's MMM, LTS and VDMS simulations. In addition to the standard comprehensive modeling, VDS has unique features of its own.

"Preview-Predictor" Driver Model.

This driver model has several modes of operation, including path-following, speed maintenance, speed change and skid recovery. Commanded steering wheel angles and throttle/brake applications are filtered to reflect human dynamic capabilities, specifically neuro-muscular dynamic characteristics.

Advanced Steering System Model

The Advanced Steering System Model is a detailed model of the steering system from the steering wheel, through the power steering unit and finally to the wheels. It replaces lumped-parameter calculations of bump-steer and bump-inclination with an analysis based on linkage lengths and mounting points. It is fully asymmetric, and has proven very useful in on-center handling studies. The model has three main parts:

Steering Column

  • Modeled as a generic two-Hooke-joint column
  • Calculation of torque and rotational motion as passed from top (steering wheel) to bottom (power steering unit) of the column, and vice versa
  • Includes phasing effects of the Hooke joints

Power Steering Unit

  • Hydraulic model of standard power steering unit
  • Includes flow rates, pressures, compliances, leakage across piston
  • Special friction/stiction model--required to properly model the rack

"Rack Loads" Model

  • Calculates loads on the end of the steering rack transmitted through the linkages
  • Determines non-fixed steer axis, bump-steer, bump-inclination
  • Forces and torques considered include tire forces and moments, drive torques, inertial reaction forces, centrifugal caster and gyroscopic torques
  • Includes corrections for non-flat ground, bump-caster, driveshaft angularity, etc.

Terrain

VDS includes a detailed terrain model of the roadway surface. The model includes elevation, bank and grade as a function of location in space-fixed coordinates. Calculation of different roadway ground planes under each wheel as occurs when driving on a crowned, cambered and curved, warped or non-uniformly banked roadway is properly modeled. Special emphasis is placed on determining the "ground point" of each tire and the proper angles for use in tire force and moment calculations.


VDS TOUR

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