J-turn

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.

Figure 1. J-turn Event

This event is designed to work with a full vehicle model that has been built through the MotionView Assembly Wizard. The event should attach to the model automatically when added through the Task Wizard. It can be used with models built manually, as long as the attachment scheme in the event is strictly followed.

The event is better described as the Fishhook test. The J-turn can be run by setting the second steer angle to zero. The event setup and sequence is described below. The default values in the event form represent a very mild input to the vehicle. Steer angles of 360 degrees and steering input rates over 300 deg/sec are typically seen in published literature regarding the J-turn. To match the input parameters to the NHTSA test specification, you must measure the parameters from the other vehicle characterization tests.

The event form is shown below. The first turn direction and second turn direction inputs are not used. Reverse the turn direction by entering negative signs in front of both the first steer angle and second steer angle inputs. The inputs are shown in the chart below and the steering inputs are shown in the diagram below.

Figure 2. J-turn Data Dialog

Figure 3.

The event sequence is as follows:

Six types of modeling element containers are used to define the event. Two sub-systems (output requests and a drive torque controller) are also included in the event.

Datasets

One dataset is used in the system and it contains the data used to describe the J-turn event. The event allows you to set turn directions and timing for the two steering inputs that define the J-turn. The wheel WZ (initial rotational velocities) are calculated values and should not be changed.

Forms

The form is the only place that you should change the data of the event. The timing and magnitude of the steer inputs can be changed on the form. The wheel WZ values are calculated using the initial speed entered on the event form and the tire rolling radius from the tire system form.

Joints

A ball joint is included in the J-turn event. The joint attaches a dummy body to the steering rack. The joint is included to make certain events work in ADAMS. Attach the dummy body to the steering rack if building a model manually.

Motions

Three motions are included in the event. The steering motion to the vehicle is provided by the steering controller and acts on a revolute joint that connects the steering column to the vehicle body. If a steering column is not included in the model, the joint acts between the steering rack input shaft and the vehicle body.

The front and rear wheel motions act on the wheel spindle revolute joints that connect the wheel hub to the knuckle. The motion is initially zero (fixing the wheels to the knuckle) so the model converges statically. The motions are deactivated after the static equilibrium analysis to allow the tires to rotate.

Solver Variables

The J-turn event consists of only one solver variable, the J-turn Steer Motion Solver variable. The solver variable is the steering wheel input motion function. The function is created using the inputs from the event form and is assigned as the steering motion input in the event template.

Templates

A template is included in the J-turn event task. The template is solver specific and only the MotionSolve template is documented. The template is inserted in the solver deck after the </Model> command and controls the execution of the event.

<ResOutput
     angle_type          = "YPR"
  />
  <ResOutput
     mrf_file            = "TRUE"
  />
  <ResOutput
     plt_file            = "TRUE"
  />
  <H3DOutput
     switch_on           = "TRUE"
     increment           = "1"
  />
  <ResOutput
     abf_file            = "TRUE"
  />
{if (tire_dataset.opt_omega.ival ==1)}
<!--Initial static analysis -->

<Simulate
	analysis_type = "Static"
	end_time      = "0.0"
/>	
{endif}

References

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