Power-off in a Straight Line
A Power-off in a Straight Line event simulates the dynamics of a vehicle due to a sudden removal of drive torque. A steer controller drives the vehicle on a straight line and the drive torque controller maintains speed until the throttle is removed. Engine motoring torque is not applied after the throttle torque is removed. A plot template is available to plot the results.
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.
- Name
- Description
- Vehicle Velocity (mph)
- The initial speed of the vehicle (miles per hour) during the steady state drive portion of the event.
- Lane Graphics Width (m)
- The width of the lane graphics in meters. The lane graphic is used for illustration only. The road surface is an infinitely wide, flat plane and is defined in the tire system by the .rdf file.
- Ground z Coordinate (mm)
- The calculated value for the ground z coordinate. Do not modify. This value is used to place the road surface and the lane graphics. It is calculated using the left front wheel center and the left front tire rolling radius entered into the tire form.
- Throttle Delay (sec)
- The absolute time, in seconds, when the throttle torque begins to be transitioned to zero.
- Throttle Step Duration (sec)
- The length of time the throttle controller takes to remove all torque from the drivetrain. The removal is done using the step function.
- End Time (sec)
- Absolute end time of the event, in seconds.
- Time Step (sec)
- The output step size. Data is written to the output plot and graphics files at this time interval.
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.
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.
- Number
- Description
- 5030
- Branching ID. 5030 is a Power-off in a straight line event.
- 70000000
- The ID of a solver array containing Driver Model Controller data. The array is in the steer controller system.
- 70000100
- The ID of a Vehicle Data array containing vehicle information. The array is in the steer controller system.
- 317001
- The value of the lane path curve.
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.