Straight Line Braking

A Straight Line Braking event simulates a vehicle decelerating at a constant rate in a straight line.

The steering wheel is normally held fixed. The Altair Driver applies torque at the wheels to slow the vehicle and appropriate output requests are included. The Straight-line Braking event follows the ISO +21994-2007 - Passenger cars - Stopping distance at straight-line braking with ABS - Open loop test method.

The Straight Line Braking 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 deceleration rate of the vehicle.
Brake start time Time at which the vehicle deceleration starts.
Transient time Time period for which the vehicle decelerates.
Initial Static and Steering Ratio
Run initial static Enables the execution of the initial static simulation.
Compute steering ratio Enables the automatic calculation of the steering ratio at the beginning of the event simulation. Turn this option off to use a different Steering ratio (default value of 16 is provided).
End Time Calculation
The parameters defined above are also used to determine the total simulation time. The total simulation time for each maneuver is specified in the Altair Drive File (.adf) as shown below:
Figure 1. Maneuvers List Block for a Straight Line Braking Event


In a Straight Line Braking event:
  • MANEUVER_1 represents the initial constant velocity part of the event.
  • MANEUVER_2 corresponds to the deceleration phase of the event.
.
The total simulation time for each maneuver is calculated using the following equations:
Maneuver Simulation Time Equation
Maneuver 1 Brake start time
Maneuver 2 Transient time

The total simulation time corresponds to the sum of the total simulation times for Maneuver 1 and Maneuver 2.

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’. When set to ‘MOTION’, the steering input is defined by the steering wheel angle. When set to ‘TORQUE’, the steering is controlled via the applied torque on the steering wheel.

    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 Event
Uses a flat smooth road for the event with no required road file.
When the Flat Event 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. The road property file used in this option overrides the road property files used in the Tire entities within the model. The road property file should be compatible with the tire property file that is used in the vehicle.
Tires
Using Tire as road selection option, the road file specified in the tire entity is used in the events simulation.

Simulation Settings

Analysis Parameters
Define the numerical and output settings for the simulation:
Parameter Name Description
Print interval The time step between successive outputs of simulation results.
Real-Time Empowered When enabled, MotionSolve builds the FMU of the vehicle and solves it in real-time.
Code generation When enabled, the C code for the MotionSolve Vehicle model excluding the driver and tire will be generated. This code can be used to compile and build an FMU, which can be used with any FMU compatible software.

For more information see the Parameters: Simulation - Attributes topic.

Dynamic Settings
Defines the simulation control parameters for a time-domain-based nonlinear dynamic analysis. For more information see the Parameters: Transient Solver - Attributes topic.
Static Settings
Defines the solution control parameters for static and quasi-static analysis. For more information see the Parameters: Static Solver - Attributes topic.

Automated Output Report

The list of outputs present in Straight Line Braking event report are as follows:
Report Name Report Signals
Steering Wheel Angle and Torque
  • Steering Wheel Angle vs. Time
  • Steering Wheel Torque vs. Time
Brake Torque
  • Left Front Brake Torque vs. Time
  • Right Front Brake Torque vs. Time
  • Left Rear Brake Torque vs. Time
  • Right Rear Brake Torque vs. Time
Vehicle Longitudinal Deceleration and Velocity
  • Longitudinal Deceleration vs. Time
  • Longitudinal Velocity 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
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
Suspension Travel
  • Left Front Suspension Travel vs. Time
  • Right Front Suspension Travel vs. Time
  • Left Rear Suspension Travel vs. Time
  • Right Rear Suspension Travel vs. Time
Pitch, Front Dive and Rear Lift
  • Pitch vs. Vehicle Deceleration
  • Front Dive vs. Vehicle Deceleration
  • Rear Lift vs. Vehicle Deceleration
Vehicle Tire Forces
  • Left Front Tire Vertical Force vs. Vehicle Deceleration
  • Right Front Tire Vertical Force vs. Vehicle Deceleration
  • Left Rear Tire Vertical Force vs. Vehicle Deceleration
  • Right Rear Tire Vertical Force vs. Vehicle Deceleration
Axle Loads
  • Front Axle Load vs. Vehicle Deceleration
  • Rear Axle Load vs. Vehicle Deceleration
Longitudinal Load Transfer
  • Left Load Transfer vs. Longitudinal Deceleration
  • Right Load Transfer vs. Longitudinal Deceleration