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3. Straight-Line-Behavior Analyses

The analyses based on the Driving Machine focus on the longitudinal dynamics of the vehicle. ADAMS/Car uses open- and closed-loop longitudinal controllers to drive your vehicle model.

The straight-line-behavior analyses include:

Acceleration test - Ramps the throttle demand from zero at your input rate (open loop) or you can specify a desired longitudinal acceleration (closed loop). You can specify either free or locked steering. An acceleration test analysis helps you study the anti-lift and anti-squat properties of a vehicle.

Braking - Ramps the brake input from zero at your input rate or lets you specify a longitudinal deceleration (closed loop). You can also specify either free or locked steering. The braking test analysis helps you study the brake-pull anti-lift and anti-dive properties of a vehicle.

Power-off straight line - This analysis allows you to examine operating behavior and directional deviations caused by suddenly lifting off the throttle pedal during a straight-line analysis. Typical results collected from the power off straight-line analysis include variations in heading direction and longitudinal deceleration. You can control the analysis using the Driving Machine. Optionally, you can depress the clutch during the throttle lift-off. In this case, you specify the duration that it takes to depress the clutch.

4. Course Analyses

Course analyses are based on the Driving Machine and are of a course-following type, such as ISO-lane change.

In an ISO-lane change analysis, the Driving Machine drives your full vehicle through a lane change course as specified in ISO-3888: Double Lane Change. You specify the gear position and speed at which to perform the lane change. The analysis stops after the vehicle travels 250 meters; therefore, the time to complete the lane change depends on the speed you input.

5. Driver-Control-File-Driven Analysis (dcf Drive…)

The driver-control-file-driven analysis lets you run a analysis described in an existing driver control file (.dcf). For the format and content of .dcf files. Having direct access to .dcf files allows you to easily perform nonstandard analyses on your full-vehicle assembly because all you have to do is to generate a new .dcf file describing the analysis.

6. Quasi-Static Analyses

Quasi-static analyses find dynamic equilibrium solutions for your full vehicle at increasing, successive values of lateral acceleration. Quasi-static analyses, in contrast to open-loop and closed-loop analyses, do not include transient effects and solve very quickly. For example, in a quasi-static analysis, a change in lateral acceleration from 0.1g to 0.5g does not show the lateral acceleration or yaw rate overshoot that a similar openloop and closed-loop analysis might show.

Quasi-static analyses use either the .__MDI_DRIVER_TESTRIG or the .__MDI_SDI_ TESTRIG.

(1) Setting up Quasi-Static Analyses

Before you submit a quasi-static analysis, you must set up the assembly to run quasi-static analyses.

You set up a quasi-static analysis by selecting the Setup button from the constant radius cornering or constant-velocity cornering dialog boxes. ADAMS/Car then adds additional modeling elements that do not exist by default in the standard MDI full-vehicle assemblies.

The additional elements reference information provided by communicators that are defined in the standard templates distributed with ADAMS/Car. The communicators are:

  • Body template: cos_body communicator: part communicator

  • Front/rear suspension template:

  • co[lr]_suspension_upright: part communicator

  • co[lr]_suspension_mount: part communicator

  • Steering template:

  • cos_steering_wheel_joint: joint communicator

  • Powertrain template:

  • co[lr]_output_torque: force communicator

  • cos_drive_torque_left: solver variable communicator

  • cos_drive_torque_right: solver variable communicator

If you are using standard ADAMS/Car templates but have removed some of the communicators, or if you built your own templates that do not include those communicators, as part of the setup procedure, ADAMS/Car prompts you to identify various elements in your assembly. You can avoid being prompted for these elements by including the communicators in the appropriate templates.

(2) Constant-Radius Cornering Analysis

You perform a constant radius cornering analysis to evaluate your full vehicle’s understeer and oversteer characteristics. The constant radius cornering analysis holds the turn radius constant and varies the vehicle velocity to produce increasing amounts of lateral acceleration. You can use the plot configuration file mdi_fva_ssc.plt in the shared ADAMS/Car database to generate the plots that are typically of interest for this analysis. Before submitting a constant radius cornering analysis, you must select the Setup button to set up your full-vehicle assembly for a quasi-static analysis.

(3) Constant-Velocity Cornering Analysis

You perform a constant velocity cornering analysis to evaluate your full vehicle’s understeer and oversteer characteristics. The constant velocity cornering analysis holds the vehicle velocity constant and varies the turn radius to produce increasing amounts of lateral acceleration. The input parameters for this analysis are the same as the steady-state cornering analysis except that the vehicle longitudinal velocity is specified instead of the turn radius. You can use the plot configuration file mdi_fva_ssc.plt in the shared car database to generate the plots that are typically of interest for this analysis.

Before submitting a constant velocity cornering analysis, you must select the Setup button to set up your full-vehicle assembly for a quasi-static analysis.

(4) Force-Moment Analysis

You perform a force-moment analysis maneuver to evaluate the stability and handling characteristics of your vehicle model. ADAMS/Car drives the vehicle at constant longitudinal speed and performs a series of simulations at different side-slip and steer angles. The simulation represents a typical test in which the vehicle is constrained on a model flat-belt tire tester. The testing method is based on the assumption that most of the stability and control characteristics can be obtained from a study of the steady-state force and moments acting on the vehicle.

The analysis consists of a series of quasi-static steady-state cornering analyses performed at different vehicle side-slip angles and at a different steer angle. Usual results of a quasistatic force-moment analysis can be presented in tabular form, or as diagrams and plots representing the computed forces and moments from the simulated test.

Before you can submit a force-moment analysis, you must set up your vehicle for a quasistatic analysis.