J-turn

The event is used to characterize the stability of vehicles. Both steer directions can be run by reversing the sign of the steering inputs. The Altair Driver is used to maintain a constant speed and standard outputs for the vehicle and tires are included in the Tire system and the Output Requests system.

The J-Turn event follows the ISO +7401-2003 - Road Vehicles-Lateral transient response test methods-Open-loop test methods. It is also designed to simulate the NHTSA fishhook test as described in DOT publication DOT HS 809 705, “Phase VIII of NHTSA’s Light Vehicle Rollover Research Program-A Demonstration of the Dynamic Tests Developed for NHTSA’s NCAP Rollover Rating System”.

The J-turn 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.
Initial power run	The time at the beginning of the event used to verify the vehicle reached the steady state.
First turn direction	Defines the steer direction used in the first turn.
First steer angle*	Angle in degrees of the initial steer input. A positive number turns the vehicle right and a negative number turns the vehicle left.
First lean angle**	The demand lean angle for the initial turn in degrees.
First step duration	Time required to input the First steer angle (a step function is used to input the angle to the steering wheel).
First turn duration	Time duration for which the steering is held fixed at the First steer angle.
Second turn direction	Defines the direction used in the second turn.
Second steer angle*	Steering angle in degrees of the second steer input.
Second lean angle**	The demand lean angle for the second turn in degrees.
Second step duration	The time required to input the Second steer angle (a step function is used to input the angle to the steering wheel).
Second turn duration	Time duration for which steering is held fixed at the Second steer angle.

*Applicable only for Cars/Trucks i.e., Non-leaning events.

**Applicable only for Two-wheeler i.e., Leaning events.

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 Swept steer event report are as follows:


Report Name	Report Signals
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
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
Axle Loads	Front Axle Load vs. Lateral Acceleration Rear Axle Load vs. Lateral Acceleration
Steering, Torque and Roll	Steering Wheel Angle vs. Lateral Acceleration Steering Wheel Torque vs. Lateral Acceleration Roll Angle vs. Lateral Acceleration Yaw Rate vs. Lateral Acceleration
Sideslip	Front Axle Sideslip vs. Lateral Acceleration Rear Axle Sideslip vs. Lateral Acceleration
CG Sideslip Angle	CG Sideslip Angle vs. Lateral Acceleration Understeer vs. Lateral Acceleration
Lateral Load Transfer	Front Load Transfer vs. Lateral Acceleration Rear Load Transfer vs. Lateral Acceleration
Steering Wheel Angle vs. Time
Vehicle CG Displacement vs. Time