Input to VDMS is through a series of ASCII and M-Files, described below. The MATLAB interface queries the user for the name of each file before a run. VDMS also supports batch files and automated operation--these are typically used for parameter studies (ie., design of experiment analysis).

The VDMS User's Manual contains detailed descriptions of each file and its contents. M-Files are also extensively commented with units and sign conventions. Sample files are provided with VDMS. These files intended to be used as templates when users create their own input data set.

Input files are as follows:

• Vehicle File: M-File describing the car/chassis and aerodynamics. Input mimics VDS and MMM vehicle data sets. View the first page of the 7 page Sample File.
• Tire File: ASCII file for the tire model. 1, 2 or 4 different tires allowed. The tire model is described in more detail on the Tire Model page of this tour.
• Control System File: M-File for driver controls, user additions (gains, etc.)
• Initial Conditions File: M-File controling integration, initialization
• Terrain File: M-File with surface friction grid and surface elevation.
• Steer, Path or Driver File: ASCII files with steering wheel angle schedule, path-following map or simple driver model commands.
• Torque, Speed or Acceleration Files: ASCII files with a schedule for individual wheel torques, vehicle speed or vehicle acceleration along the path.

The vehicle is represented as a lumped-parameter system. The model contains 15 major degrees-of-freedom: 6 for the sprung mass, 4 vertical for each wheel, 4 rotational about the wheel spin axis and 1 for the steering wheel. Other features modeled include:

• Independent front suspension
• Independent or axle rear suspension
• Full suspension kinematics, tabular or polynomial-based
• Comprehensive suspension compliances
• Ackermann steering corrections
• Nonlinear suspension bump and rebound stops
• Front and rear anti-roll bars
• Table-lookup dampers (shock absorbers)
• Aerodynamic drag and lift/downforce
• Tire rolling resistance and induced drag
• Engine Torque as a function of throttle position and engine speed
• Transmission with up to 20 gears
• Choice of locked, open or limited slip front, rear and center differentials
• Choice of front wheel drive, rear wheel drive or four wheel drive
• Four wheel brakes with front/rear proportioning and simple ABS model
• Ability to slow to a stop, start from zero velocity, lift any to all wheels off the ground and simulate rollover
• Variable road surface coefficient
• Terrain elevation changes including hills, banking and jumps

MRA regularly adds features at the request of specific customers. Additionally, VDMS has been developed to allow for easy substitution of proprietary user blocks or to develop active control systems. VDMS can be run in either USCS (English) or SI (Metric) units.

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