CarSim Math Models

Here are some features of the CarSim mathematical models.

Control Inputs

The three main control inputs involve steering, braking, and speed. CarSim has options for open-loop and closed-loop inputs for steering, braking, throttle, and gear shifting. There are also options for building complex control sequences as a series of "events," where a new control can be triggered by any output variable reaching a specified value.

Environmental Inputs

CarSim includes an advanced description of 3D road surfaces. You can quickly build descriptions of roads with arbitrary horizontal, vertical, and cross-elevation geometry. Friction between the tire and the ground is specified as a function of distance along the road and lateral position relative to the centerline.

CarSim includes aerodynamic effects and wind inputs.

3D Vehicle Dynamics

The equations of motion in the CarSim math models are valid for full nonlinear 3D motions of rigid bodies. The major kinematics and compliance effects of the suspensions and steering systems are specified with properties that can be measured directly. Details of the linkages and gears in the suspensions and steering systems are not needed, reducing the amount of information needed to obtain accurate predictions.

Many of the components that have the greatest effect on handling, braking, and acceleration are represented with nonlinear tables of measurable data. For example, CarSim uses detailed nonlinear tire models, nonlinear spring models, and other nonlinear component models.

Events

Complicated sequences of inputs can be specified as events. For example, accelerate until a speed is reached, then shift to neutral and coast down, then apply the brakes until a low speed is reached, then accelerate, etc. Conditions can also be in place for changing vehicle properties. For example, change the tire data for one wheel if the friction under that wheel drops below some limit.

Outputs

You can view simulation results with a virtual camera (animation) and with plots of output variables with a single button click. The number and order of the output variables can be specified at run-time from a list of hundreds of available variables.

Extending a CarSim Model

The CarSim math models include more than 160 inputs that you can specify in Simulink or with your own C code. These inputs include all control and environmental inputs, and all forces and moments generated by the powertrain, brakes, steering system, tires, and some suspension components. These inputs are used to extend the CarSim math models by defining them with MATLAB/Simulink, available from The MathWorks, Inc, or with custom C code.

CarSim Information