Power-off in a Straight Line

Figure 1. Power-off in a Straight Line Event

Figure 2. Top View of a Power-off in a Straight Line Path

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

In this event, the vehicle drives at the vehicle velocity down a straight road and follows a line on the centerline of the road using the driver controller. The drive torque controller maintains the vehicle speed. At the throttle delay time, the drive torque begins to be removed and is removed over the throttle step duration time using a function. The event ends at the end time. Data is output to the plot and graphics files every time step seconds.

The test is a common vehicle characterization test and is used to understand the vehicle response to a sudden removal of throttle torque. Vehicle dynamics engineers are typically interested in the vehicle state responses and the tire behavior during the event. All of these signals are saved to the plot file.

The typical vehicle velocity and drive torque responses are plotted below for the default event times using the Altair reference model. Many other signals are available, but these two plots illustrate the event inputs and response well.

Figure 3. Power-off in a Straight Line

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

Curves

A single curve is included in this event. The steering controller follows the path defined by the curve. The curve is on the centerline of the lane path (global Y=0) and uses the values of the odd numbered cone points to parametrically define the X and Z coordinates.

Datasets

One dataset is used in the system and it contains the data used to describe the Power-off in a Straight Line event. The event allows you to set the vehicle control, lane graphics width, throttle delay, throttle step duration, end time, and time step. The wheel rotational velocities and ground height (shown in a blue background below) are calculated values. You can change the vehicle event data in the event form.

Forms

The form is the only place that you should change the inputs for the Power-off in a Straight Line event. Vehicle velocity, lane graphics, throttle delay, throttle step duration, end time, and time step are the parameters that can be changed. The ground z coordinate is a calculated value and should not be changed.

Graphics

Eleven graphics are defined in the event. The graphics define the cones and the straight road surface and should not require any user input. A full description of the graphics elements can be found here.

The straight road graphics are included to illustrate the path being driven. The flat road surface is displayed at the calculated tire patch point and is the width defined in the event form and is approximately 400 meters long. The ten cones are defined parametrically to be every 100 meters along the lane path, at the edge of the road (using the lane width from the event form and the cone radius). Straight road graphics should never require editing unless the event is being fundamentally changed.

Figure 4. Cone Graphics

Figure 5. Power-off in a Straight Line - Road Graphics

Joints

A ball joint is included in the Power-off in a Straight Line 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

Five markers are included in the Power-off in a Straight Line event. The path origin is the origin of all lane change graphics and is parametrically defined to be the CG of the vehicle body. The four remaining markers are used to define the four corners of the road surface graphic element. The markers refer to points and the points contain the parametric logic to define the road surface.

None of the markers should require any user input.

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 wheel lock motions are deactivated after the convergence of the static analysis to allow the tires to rotate during the dynamic analysis.

Points

Fifteen points are defined in the event. All points are used to create the lane graphics and graphics for the cones used to illustrate the lanes. The points contain parametric logic to define their X, Y, and Z locations. Points are approximately every 100 meters along the road edge. You should not need to modify any points.

Solver Variables

The Power-off in a Straight Line event contains one solver variable, the Steer Path variable. The Steer Path variable defines the path for the steer controller. The event uses the lane path curve as the desired path.

Templates

A template is included in the Power-off in a Straight Line event. 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.

The template for this event contains the standard elements of events, along with a Motion_Joint command. The command assigns the motion of the steering to be the solver variable (sv_path.idstring), which enables the steering controller functionality.

<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}
<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.end_time.value}"
     num_steps		 = "{ds.end_time.value/ds.time_step.value}"
  />
<Stop/>

References

ISO +4138-2004 - Passenger cars — Steady-state circular driving behaviour — Open-loop test methods.