Braking In a Turn

Standard outputs for the vehicle and tires are included in the event. A steer controller drives the vehicle on the path, a drive torque controller maintains constant speed until the brakes are applied, and the brake torque controller applies a torque to maintain the constant braking deceleration.

Figure 1. Braking in a Turn event

Figure 2. Top View of a Braking in a Turn event

Figure 3. Vehicle Model with Body Graphics

The event is designed to simulate a vehicle braking while turning in a constant radius corner. Test conditions, such as the vehicle lateral acceleration, longitudinal deceleration and the test track corner radius are parametric in the event and can be easily modified to match the test conditions at the customer's track.

Figure 4. Path for the Braking in a Turn Test

Note:

• The vehicle is driven at a constant speed until the braking event begins using the drive torque controller.
• The steer controller steers the vehicle using a motion at the steering wheel or steering gear input shaft and is described here.
• The vehicle velocity is calculated using the lateral acceleration, the circle radius and the equation v=sqrt(radius*acceleration). A number of unit conversion factors are required to convert to the model units of millimeters and seconds.
• The brake torque controller maintains the desired deceleration.
• You are responsible for entering the braking and event end times that are consistent with the path and the time required for the vehicle to respond to the various inputs.

Nine types of modeling element containers are used to define the event. Four sub-systems (output requests, steer controller, drive torque controller, and brake 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 Braking in a Turn event. The event allows you to set the lateral acceleration, circle radius, turn direction (left or right), end of simulation time, time to apply brakes, desired deceleration and brake step duration. 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 lane change event. lateral acceleration, circle radius, time to apply brakes, end of simulation time, desired deceleration and brake step duration are the parameters that can be changed. The turn direction can be either left or right, and it is user-dependent. 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 Braking in a Turn event form. Skidpad graphics should never require editing unless the event is being fundamentally changed.

Joints

A ball joint is included in the Braking 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 Braking in a Turn 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 is provided by the steer controller to steer the vehicle, and it acts on a revolute joint that connects the steering wheel 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 modify any points.

Solver Variables

The Braking 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"
  />
  <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_str_path.idstring})"
/>
<Simulate
	analysis_type = "Transient"
	end_time      = "{ds.end_of_sim.value}"
	num_steps     = "{ds.end_of_sim.value*50}"
/>

<Stop/>

References

ISO 7376-2006 - Passenger cars - Braking in A Turn - Open-loop test method.