Straight Line Acceleration

A Straight line acceleration event simulates a vehicle accelerating at a constant rate in a straight line.

The event is designed to characterize the chassis behavior during acceleration. The Altair Driver maintains the acceleration rate in the model. Output Requests are included to measure the vehicle behavior, tire response, and other common vehicle system metrics. A plot template is available to plot the results.

The Straight-line acceleration event is supported by the Cars & Small Trucks, Heavy Trucks, and Two-Wheeler vehicle libraries. Automated output reports are available to plot the results.

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).
Velocity Initial vehicle velocity.
Desired deceleration Desired Acceleration rate of the vehicle.
Brake start time Time at which the vehicle deceleration starts.
Transient time Time period for which the vehicle decelerates.

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
For more information see the Altair Driver Mathematical Methods topic.
Leaning events (Two-wheelers)
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
  • 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
    Ki Integral gain for the lateral error controller
    Kd Derivative gain for the lateral error controller
    For more information see the Leaning Two and Three Wheeler Vehicles and Gain Tuning for Leaning Two and Three Wheeler Vehicles topics.

Signal Settings

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 Straight line acceleration event report are as follows:
Report Name Report Signals
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
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
Tire Longitudinal Slip
  • Left Front Tire Longitudinal Slip vs. Time
  • Right Front Tire Longitudinal Slip vs. Time
  • Left Rear Tire Longitudinal Slip vs. Time
  • Right Rear Tire Longitudinal Slip vs. Time
Vertical Longitudinal Deceleration and Velocity
  • Longitudinal Deceleration vs. Time
  • Longitudinal Velocity vs. Time
Suspension Travel
  • 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 Wheel Angle and Torque
  • Steering Wheel Angle vs. Time
  • Steering Wheel Torque vs. Time
  • Drive Torque vs. Time
Pitch, Front Lift and Rear Squat
  • Pitch vs. Longitudinal Deceleration
  • Front Lift vs. Longitudinal Deceleration
  • Rear Squat vs. Longitudinal Deceleration
Vehicle Tire Forces
  • Left Front Tire Vertical Force vs. Longitudinal Acceleration
  • Right Front Tire Vertical Force vs. Longitudinal Acceleration
  • Left Rear Tire Vertical Force vs. Longitudinal Acceleration
  • Right Rear Tire Vertical Force vs. Longitudinal Acceleration
Axle Loads
  • Front Axle Load vs. Longitudinal Acceleration
  • Rear Axle Load vs. Longitudinal Acceleration
Longitudinal Acceleration
  • Left Load Transfer vs. Longitudinal Acceleration
  • Right Load Transfer vs. Longitudinal Acceleration