Steer Release in a Turn

A Steer Release in a Turn event simulates a vehicle cornering at a constant radius and the dynamics of the steering wheel being released while in the corner. A steer controller is used to drive the constant radius curve, a drive torque controller 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.

Figure 1. Steer Release in a Turn event

Figure 2. Top View of a Steer Release in a Turn event (Vehicle is Extremely Small)

Figure 3. Vehicle Model with Body Graphics

Description

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 sequence is described in the chart below:

Figure 4. Event Diagram - Steering Release in a Turn

The steer controller drives the vehicle on the straight and the constant radius path by applying motion to a joint at either the steering wheel or the steering rack input shaft (if no steering column is included). The controller is disabled at the steer release time.

The drive torque controller is included to maintain constant speed during the entire event. The drive torque controller applies a torque to the drivetrain and uses a P-D controller (with user-defined parameters) to control the speed of the vehicle.

The entry length straight road section is included to allow the vehicle model to settle into steady-state, straight line driving. The vehicle turns into the constant radius corner and should be allowed to reach steady-state cornering before releasing the steering wheel.

Attachments

The event uses the standard event attachment. The attachments resolve automatically if the model is built through the Model Wizard. The attachments contain the minimum data the event needs to run the analysis. The attachments are standard for most events.

Datasets

One dataset is used in the system and it contains the data used to describe the Steer Release in a Turn event. The event allows you to set the lateral acceleration, circle radius, turn direction (left or right), steer release time and the turn direction (left or right). The initial velocity, wheel rotational velocities and ground height are calculated values and should not be changed.

Forms

The form is the only place that you should change the data of the event. Lateral acceleration, circle radius, turn direction (left or right), and steer release time are the parameters that can be changed. The ground z coordinate is a calculated value and is calculated using the wheel CG Z location and the tire rolling radius from the tire data form.

Graphics

One graphic is defined in the event. The graphics define the road surface graphics and should not require any user input. A full description of the graphics can be found here.

Skidpad graphics are included to illustrate the path being driven, and are defined parametrically using the data in the event form. Skidpad graphics should never require editing unless the event is being fundamentally changed.

Figure 5.

Joints

A ball joint is included in the steer release in a 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.

Markers

One marker is included in the event. The path origin is the origin of skidpad graphics and is parametrically defined to be the CG of the vehicle body. The markers refer to points and the points contain the parametric logic.

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 initial static analysis to allow the tires to rotate during the dynamic analysis.

Points

Two points are defined in the event. All points are used to create the skidpad graphics. The points contain parametric logic to define their X, Y, and Z locations. You should not need to modify any points.

Solver Variables

The Steer Release in a Turn event consists of only one solver variable, the Steer Path variable, which calls a user subroutine to apply an input at the steering wheel in order to follow a desired path.

Templates

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"
  />
{if (tire_dataset.opt_omega.ival ==1)}
<!--Initial static analysis -->

<Simulate
	analysis_type = "Static"
	end_time      = "0.0"
/>	
{endif}
 <Deactivate
	element_type = "MOTION"
	element_id = "{mot_frnt_wheel.l.idstring}"
/>
<Deactivate
	element_type = "MOTION"
	element_id = "{mot_frnt_wheel.r.idstring}"
/>
<Deactivate
	element_type = "MOTION"
	element_id = "{mot_rear_wheel.l.idstring}"
/>
<Deactivate
	element_type = "MOTION"
	element_id = "{mot_rear_wheel.r.idstring}"
/>
{if (tire_dataset.opt_omega.ival ==2)}
<!--Initial static analysis -->

<Simulate
	analysis_type = "Static"
	end_time      = "0.0"
/>	
{endif}
<Deactivate
	element_type = "JPRIM"
	element_id = "{j_clamp_1_body.idstring}"
/>
<Deactivate
	element_type = "JPRIM"
	element_id = "{j_clamp_2_body.idstring}"
/>    
 
<Motion_Joint
     id                  = "{wh_motion.idstring}"
     expr                = "VARVAL({sv_path.idstring})"
  />    

<Simulate
     analysis_type       = "Transient"
     end_time            = "{ds.release_tim.value}"
     print_interval      = "0.02"
  />
<Deactivate
	element_type = "MOTION"
	element_id = "{wh_motion.idstring}"
/>

 <Reference_Variable
    id                  = "{sv_path.idstring}"
    type                = "EXPRESSION"
    expr                = "0.0"
 />
  
 <Simulate
      analysis_type       = "Transient"
      end_time            = "{{ds.release_tim.value}+5}"
      print_interval      = "0.02"
  />
  
<Stop/>

References

ISO +17288-1-2011 - Passenger cars - Free-steer behaviour - Part 1: Steering-release open-loop test method.