A Constant radius event simulates a vehicle driving in a circular path, typically with
increasing speed. The event predicts the vehicles roll and understeer characteristics with
increasing lateral acceleration.
The event maintains a constant turn radius and varies the vehicle velocity to produce
increasing amounts of lateral acceleration. Steering and torque controllers maintain the
path and the speed of the vehicle through the event.
The constant radius event is supported by the Cars & Small Trucks, Heavy Trucks, and
Two-Wheeler vehicle libraries. Automated output reports are available to plot the
results.
The constant radius event follows the ISO +4138-2004 - Passenger cars — Steady-state
circular driving behavior — Open-loop test methods. Figure 1. Constant Radius Event
Parameters
Parameter Name
Description
Units
Describes the Length, Velocity, and Acceleration units.
Length (Model, m, ft)
Velocity (Model, m/s, km/h, mph).
Acceleration (Model, m/s2, g’s).
Radius
Radius of the circle that the vehicle CG follows during the constant radius
portion of the event.
Initial straight
Straight distance section of the event before the constant radius
portion.
Initial velocity
Initial vehicle velocity.
Final velocity
Final vehicle velocity desired in the simulation.
Initial lateral acceleration
Estimated initial lateral acceleration. This value is not editable and is
calculated using the initial speed and the radius parameters.
Final lateral acceleration
Estimated final lateral acceleration. This value is not editable and is
calculated using the initial speed and the radius parameters.
Turn direction
Direction the vehicle turns during the event (as seen by the driver).
Transient time
Time duration for which vehicle accelerates/decelerates after achieving
steady state.
Controller Settings
Non-leaning events (Cars/Trucks)
LONGITUDINAL – TRACTION CONTROLLER SETTINGS
Use additional control: Enables the additional feedback control for the traction
control. The gains for the controller can be edited by toggling this check
box.
Kp
Proportional gain for the feedback PID controller
Ki
Integral gain for the feedback PID controller
Kd
Derivative gain for the feedback PID controller
LATERAL – STEERING CONTROLLER SETTINGS
Altair Driver uses Feedforward steering controller for non-leaning vehicles like
Cars and Trucks. The following settings can be edited by the user.
Look ahead time
Look ahead time for the feedforward model to evaluate future states
of the vehicle
Prediction step size
Maximum step size, used by the Driver feedforward steering
model
Use additional control: Enables the additional feedback control for the traction
control. The gains for the controller can be edited by toggling this check
box.
Kp
Proportional gain for the feedback PID controller
Ki
Integral gain for the feedback PID controller
Kd
Derivative gain for the feedback PID controller
LATERAL – STEERING CONTROLLER SETTINGS
The Lean PID and Lateral Error PID controllers only apply to leaning vehicles
(for example, motorcycles and scooters).
Steer control: Control mode for
steering can be switched between ‘MOTION’ and ‘TORQUE’
Lean control
The Lean PID takes as input a demand lean angle and outputs front fork
(steering) angle. For open loop events the lean angle demand is a function
of time. For closed loop path following events the demand lean angle is
computed based on the vehicle speed and the path curvature with a correction
for lateral path error.
Kp
Proportional gain for the lean controller
Ki
Integral gain for the lean controller
Kd
Derivative gain for the lean controller
Lateral error control
The Lateral Error PID takes as input the predicted lateral path error and
outputs an increment to the demanded lean angle. The lateral error is
computed by predicting the vehicle’s lateral position relative to the path
by the look ahead time in the future. The Lateral Error PID acts to lean the
vehicle toward the path.
Look ahead time
Look ahead time for the feedforward model to evaluate future
states of the vehicle
Kp
Proportional gain for the lateral error controller
Use the signal settings to set minimum, maximum, smooth frequency and initial values for
Steering, Throttle, Brake, Gear, and Clutch signals output by the driver.
The smoothing frequency is used to control how fast the Driver changes signals. Only closed
loop control signals from the Driver are smoothed. Open loop signals are not smoothed.
Road Settings
Three options are available to specify the road in the event, Flat Event, Road File, and Tires.
Flat Road
Uses a flat smooth road for the event with no required road file.
When the Flat
Road is selected, the Graphics Setting option is available with the following
parameters:
View path centerline: Enables the visualization of the event path.
This check box is disabled for open loop events without a path.
View grid graphics: Enables the visualization of the road grid graphics.
When view grid graphics check box is toggled, road grid parameters can be
edited in the Grid Settings tab.
Grid length
Defines the length of the road. Enter a positive value in the
model units.
Grid Width
Defines the width of the road. Enter a positive value in the
model units.
Grid X offset
Gives a distance offset to the road graphics in the longitudinal
direction. Enter a positive value in the model units.
Grid Y offset
Gives a distance offset to the road graphics in the lateral
direction. Enter a positive value in the model units.
Road File
The road file option enables the selection of a road file to be used in the event.
Using this option, all tires in the model consider the event specified road file
instead of the file included in the tire entities.
Tires
Using Tire as road selection option, the road file specified in the tire entity is
used in the events simulation.
Automated Output Report
The list of outputs present in a Double lane change event report are as follows:
Report Name
Report Signals
Steering Input and Accelerations
Steering Wheel Angle vs. Time
Steering Wheel Torque vs. Time
Lateral Acceleration vs. Time
Longitudinal Acceleration vs. Time
Vehicle Velocities
Yaw Rate vs. Time
Longitudinal Velocity vs. Time
Lateral Velocity vs. Time
Vehicle Slip Angles
Front Sideslip Angle vs. Time
Rear Sideslip Angle vs. Time
CG Sideslip Angle vs. Time
Roll Angle
Roll Angle vs. Time
Steer/Suspension Travel
Front Steer Angle vs. Time
Rear Steer Angle vs. Time
Front Suspension Travel-left vs. Time
Front Suspension Travel-right vs. Time
Rear Suspension Travel-left vs. Time
Rear Suspension Travel-right vs. Time
Steering, roll and torque
Steering Wheel Angle vs. Lateral Acceleration
Steering Wheel Torque vs. Lateral Acceleration
Roll Angle vs. Lateral Acceleration
Vehicle Path
Vehicle Slip vs. Acceleration
Front Axle Sideslip vs. Lateral Acceleration
Rear Axle Sideslip vs. Lateral Acceleration
CG Sideslip Angle vs. Lateral Acceleration
Steering Wheel Angle vs. Vehicle Sideslip Angle
Tire Lateral Slip
Left Front Tire Lateral Slip vs. Time
Right Front Tire Lateral Slip vs. Time
Left Rear Tire Lateral Slip vs. Time
Right Rear Tire Lateral Slip vs. Time
Vertical Tire Forces
Left Front Tire Vertical Force vs. Time
Right Front Tire Vertical Force vs. Time
Left Rear Tire Vertical Force vs. Time
Right Rear Tire Vertical Force vs. Time
Lateral Tire Forces
Left Front Tire Lateral Force vs. Time
Right Front Tire Lateral Force vs. Time
Left Rear Tire Lateral Force vs. Time
Right Rear Tire Lateral Force vs. Time
Longitudinal Tire Forces
Left Front Tire Longitudinal Force vs. Time
Right Front Tire Longitudinal Force vs. Time
Left Rear Tire Longitudinal Force vs. Time
Right Rear Tire Longitudinal Force vs. Time
Wheel Aligning Torques
Left Front Tire Aligning Torque vs. Time
Right Front Tire Aligning Torque vs. Time
Left Rear Tire Aligning Torque vs. Time
Right Rear Tire Aligning Torque vs. Time
Vertical Tire Forces vs. Lateral Acceleration
Left Front Tire Vertical Force vs. Lateral Acceleration
Right Front Tire Vertical Force vs. Lateral Acceleration
Left Rear Tire Vertical Force vs. Lateral Acceleration
Right Rear Tire Vertical Force vs. Lateral Acceleration
Lateral Load Transfer
Front Lateral Load Transfer vs. Lateral Acceleration
Rear Lateral Load Transfer vs. Lateral Acceleration
