J-turn

A J-turn event simulates a vehicle response to a large steer in one direction, a dwell time to allow the vehicle to react, and a large steer in the opposite direction, with an additional reaction time.

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. A plot template is available to plot the results.

A better name for the event is Fishhook maneuver. The event is designed to be able 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 typically needs to be rerun at a variety of steer inputs and event timing to obtain the worst possible vehicle reaction.

The parameters available in the J Turn event are detailed in the following table:

Parameter	Description
Units	Velocity unit selection (Model, m/s, km/h, mph).
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.
First step duration	Time required to input the First steer angle (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.
Second step duration	The time required to input the Second steer angle (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.
Print interval	Time interval of data output to the plot file (.plt) and graphics file (.h3d).

*Applicable only for Two-wheeler events.

References

ISO +7401-2003 – Road Vehicles-Lateral transient response test methods-Open-loop test methods.