Addendum 1 eBTD Model Assessment

From: Transport Canada

1. Introduction

The electronic Belt-fit Test Device model ( eBTD ) is a predictive numerical model based on the fundamental physics of measuring the fit of a seat belt on a physical Belt-fit Test Device (BTD). Calculations involved in obtaining solutions to this model require computer code and would be subjected to estimation errors and accuracy limitations. Since the results of this model will be used in the evaluation of belt fit, as well as in the design and development process, a verification, validation and confirmation process (VVC) is required to quantify the level of confidence in predictions made with models developed using this tool.

The American Society of Mechanical Engineers (ASME) Verification and Validation Standards Committee has established a general procedure to be followed in the field of computational solid mechanics.

  • Verification is the process of determining that a model implementation accurately represents the developer’s conceptual description of the model and the solution to the model. Therefore, verification is concerned with identifying and removing errors in the model by comparing numerical solutions to analytical or highly accurate benchmark solutions.
     
  • Validation is the process of determining the degree to which a model is an accurate representation of the real world from the perspective of the intended uses of the model. Therefore, validation is concerned with quantifying the accuracy of the model by comparing numerical solutions to experimental data.
     
  • Confirmation is the final process of the evaluation whereby an independent agent takes on the task of comparing the final outcome of both the mathematics and physics of the model. This is done in cooperation with both the software and hardware developers with real world physical data in conjunction with its proper modeling parameters in a real time confirmation exercise.

Verification deals with the mathematics associated with the model, whereas validation deals with the physics associated with the model. Because modeling and/or mathematical errors can cancel, giving the impression of correctness (right answer for the wrong reason), verification must be performed before validation begins. The confirmation task then serves as a feed back loop to the overall modeling approach.

Verification and validation are processes that collect evidence of a model’s correctness or accuracy for a specific set of parameters; thus, VVC cannot prove that a model is correct and accurate for all possible conditions and applications, but rather provide evidence that a model is sufficiently accurate.

2. Requirement for Competing Software

The process required for any computer model to be used in eBTD simulation necessitates that the software be fully evaluated using the approach shown in Figure 1 and includes the following three phases:

Verification: by the software developer;
Validation: by the hardware developer.
Confirmation: by a third party in conjunction with both developers.

The current RAMSIS eBTD has achieved a confirmation score of the pass/fail criteria of 97% as described in article 6.5 of section 3.42. Any other software package and modeling approach has to achieve at least the same level of VVC as the currently developed RAMSIS eBTD V1.7 program.

 


Figure 1 - V&V&C process

3. Technical Requirements

The requirements described herein will be applied to vehicles as specified in the MOU.

3.1 Application

The belt fit requirement described herein applies to the front outboard seating positions in passenger carrying vehicles with GVWR less than 8 500 lbs.

3.2 Test Devices

The belt fit requirements are fulfilled if the requirements of either section 3.2.1 or 3.2.2 have been satisfied.

3.2.1 Belt Fit Software

Belt fit is measured using the eBTD software, version 1.7 or subsequent validated versions, developed by Human Solutions of North America Inc. or a comparable validated software package requirements for which have been specified in section 2. Transport Canada will evaluate the vehicle using the same software version used by the manufacturer.

3.2.2 Physical Manikin

Belt fit is measured using the Biokinetics BTD, as defined by assembly drawing 011-01-096, when used in accordance with the Operational Manual for the Belt fit Test Device (Biokinetics Document D04-03).

3.3 Belt Fit Criteria

3.3.1 Scales

Technical criteria are modified to include scale endpoints per agreements made at the February 4, 2003 JWG-AIR meeting in Toronto, Canada, and the July 22, 2004 TWG meeting in Detroit, Michigan;

Clavicle Scale: 7 cm ≤ x ≤ 14 cm
Sternum Scale: 12 cm ≤ x ≤ 22 cm
Lap Scale:  x ≥ 1.5 cm on inboard and outboard scales

3.3.2 Scale Contact

Contact between the belt and both eBTD and BTD must occur (1) at or above the clavicle scale and (2) at the outboard lap scale.

Contact between the belt and both eBTD and BTD is not required at (1) the sternum scale and (2) inboard lap scale. The offset at the inboard lap scale must be less than 7.0 mm. For BTD, the offset measured at the sternum scale must be less than 12.0 mm.

3.4 Belt Fit Requirements

3.4.1 Test Procedure

The following procedure should be followed to properly assess belt fit. Installation of the physical BTD must be conducted according to the Operational Manual for the Belt fit Test Device (Biokinetics Document D04-03). For the eBTD , the torso angle must be set to 22 degrees unless otherwise specified by the manufacturer "nominal design torso angle" and the seat position must be set to the mid position, as defined by the physical BTD requirements. The requirements are represented by the flow chart in Figure 2.

 


Figure 2 - Test Procedure for Evaluation of Belt Fit

  1. Run the eBTD model at the design H-point. As outlined in Chapter (2).
    1. If the model reports “PASS”, then perform the ECE-R17 H-point check as per step 4.
  2. If the model reports “NO PASS”, the system should either be redesigned and rechecked per number (1) or, checked by the manufacturer against the belt fit criteria using the physical Belt fit Test Device (BTD) as defined by the Biokinetics assembly drawing 011-01-096.
  3. If the belt fit falls within the BTD scale criteria, then the vehicle fulfills the requirements.
    1. If the belt fit falls outside the scale criteria of the BTD, then the situation is cause for review between Transport Canada and the manufacturer.
  4. ECE-R17 H-point criteria – The H-point of the vehicle should be measured by the standard HPM (SAE J826) device. The measured H-point should lie within the perimeter of the 50 mm square area as shown in Figure 3.
    1. If the belt fit fulfills the ECE-R17 H-point requirement, then the vehicle fulfills the requirements.
    2. If the belt fit does not fulfill the ECE-R17 H-point requirement, then the situation is reviewed between Transport Canada and the manufacturer.

 


Figure 3 - ECE-R17 H-point Requirement

4. Technical Limitations and Proposed Solutions

4.1 Consideration of Offsets

Offsets are described as the distance in the x-direction between the belt webbing and the BTD scales. It is necessary to include offsets in order to represent actual belt positioning conditions. Some of the reasons that support the need to allow offsets are listed below.

Vehicle evaluations using the physical BTD have frequently shown minor lap scale offsets caused by the buckle latchplate bridging across the lap scale. If the buckle contacts the lap form outboard of the lap scale, the latchplate may hold the webbing above the lap scale. This non-contact with the scale is an artifact of the hard, unyielding surface of the BTD. When an occupant wears a seat belt, the soft skin and clothing conform to the shape of the buckle, and the belt stays in contact with the thighs. Manufacturers requested an allowance of a small lap scale offset in 1994 to accommodate this artifact in physical BTD results. Similar results can occur with the eBTD .

There are also belt routing differences in static and dynamic vehicle environments. The addition of voluntary advanced restraint technologies can mitigate the effects of slack in shoulder belts. Pretensioners can remove slack from the belts at the beginning of a crash, eliminating or minimizing the effect of initial belt slack or offset on dummy responses. Pretensioners may be needed in some vehicles to meet the dummy response criteria proposed for MVSR 208.

Activation of pretensioners could also affect scale offsets on the physical BTD at both the lap and clavicle scales; however, the BTD evaluation is done without activating any pretensioners. The hard surface of the physical BTD could not accurately evaluate the effect of pretensioning on belt fit. The eBTD also does not consider the effect of belt tension, but it could partially evaluate the effects of buckle pretensioners if the final position of the buckle was used as input into the computer model. Adding a buckle pretensioner to a vehicle design can adversely affect BTD and eBTD results, while improving belt fit and performance during real-world crashes because the initial latchplate position may be somewhat higher and further inboard with a buckle pretensioner due to packaging requirements and added stiffness in the pretensioner buckle mounting compared to a non-pretensioner buckle mounting.

The eBTD calculation method presents another cause for requiring allowances for offsets. Routing of the inboard lap belt is sensitive to buckle position and the current calculation of buckle position is imprecise. This calculation is likely sensitive to the stiffness parameter in some designs and may be sensitive to the assumed initial buckle position.

As a result of the above concerns, the Technical Working Group has agreed on the following resolutions:

  1. Initial buckle position should be considered at the highest possible position in its free motion range.
     
  2. Belt contact at the clavicle scale must occur anywhere above or at the clavicle scale.
     
  3. To accommodate the sternum contours of the BTD and eBTD , an allowance for the belt offset has been included.
     
  4. To adjust for the unyielding surface of the BTD and eBTD , an allowance for the belt offset has been included, as discussed earlier in this chapter.
     
  5. The allowable score for the clavicle scale has been adjusted to meet the requirements of a vehicle equipped with a pre-tensioning device.

4.2 Limitations of the Software

4.2.1 Stiffness Parameter for class B.2

The stiffness parameter can affect the eBTD result. Therefore, the following section proposes countermeasures that may be used to define this parameter.

Option # 1:

The manufacturer may choose a stiffness parameter value as input to the eBTD . The manufacturer may use any of the following as the basis for the selection:

  • Experience from similar anchorages of the same buckle stalk in similar packages.
  • Physical tests to determine the final position of the buckle with respect to the seat.
  • Analytical test scenarios as applied to reference tables.

The manufacturer must provide the technical basis of the selection in the form of a CAD estimation, trial and error data, internal reference table or other justification.

Option # 2:

Stiffness parameter values in the software will correspond to a specific force-deflection response. These values should be developed based on systematic evaluation of typical stalk material and should correspond to a specific range of response characteristics for a given parameter value as recommended by Biokinetics protocol of August 2004.3

4.2.2 Limitations of Class B.1

Additional degrees of freedom are to be added to simulate some design variations in this anchorage class. The manufacturer may choose an additional 'degree of freedom' value as input to the eBTD . The manufacturer must report the justification for the value selection and may use any of the following as the basis for the selection:

  • Experience from similar anchorages of the same buckle stalk in similar packages.
  • Physical tests to determine the final position of the buckle with respect to the seat.
  • Analytical test scenarios as applied to reference tables and recommended by the Biokinetics protocol.4

The manufacturer must provide the technical basis of the selection in the form of CAD estimation, trial and error data, internal reference table, or other justification.

4.2.2.1 Seatbelt Interaction

The effects of seat cushion interaction or component contact may not be predictable during the design stage of the vehicle. Likewise, it may not be possible to predict the severity or effect of such interaction or contact. Therefore, two scenarios and their solutions are outlined below.

4.2.2.2 Predictable Interaction or Contact

The manufacturer can predict the effects of seat interaction or component contact during the design stage. In this case, the eBTD simulation should proceed; however, the belt should be rerouted using the "integrated seat" class definitions (A.2, B.1, and C.1).

4.2.2.3 Unpredictable Interaction or Contact

The manufacturer cannot predict the effects of seat interaction or component contact during the design stage. In this case, the manufacturer should calculate the belt routing with the assumption that there is no or minor interaction or contact.

If an actual vehicle check shows belt routing that differs significantly from the modeled routing due to seat interaction or component contact, then only the ECE-R17 requirement can be verified for that vehicle until such time as:

  • additional anchorages are added to the eBTD anchorage library; or
  • additional rerouting features are added to the eBTD to simulate seat interaction or component contact.

4.2.3 Software Applicability

The eBTD was developed on the basis of an initial static belt position on the BTD torso form. Restraint effects during impact and active components that offer occupant restraint (pretensioners, airbags, etc.) are beyond the scope of this evaluation methodology. Software features limit its applicability to the following conditions:

  • Anchorages must be able to be defined by one of the seven anchor classes.
  • eBTD does not consider the effects of seat characteristics such as cushion type, cushion height variations, material, seat back geometrical configuration, belt tension or friction effects.
  • Dynamic belt systems such as pretensioners are not considered in the eBTD routing simulation. There is currently insufficient information to predict the final belt geometry at the time of the impact based on the static routing observed prior to the activation of a pretensioner.
  • Correct vehicle design data with the seat in the BTD test position is essential.
  • The program user may experience some difficulty in identifying and applying the correct anchorage classification.
  • Program instructions on identifying the initial anchorage positions are followed correctly.
  • Since the program does not simulate the anchorage volume or thickness, it may produce inboard lap scale contact results that differ from the physical BTD.
  • Belt webbing contact with the seat cushion, which affects belt routing, can now be simulated by the program but seat contour CAD data is required to apply this feature.

5. Confirmatory Data

5.1 eBTD

On an annual basis, the Manufacturer will identify to Transport Canada (in a non-confidential fashion) each new model vehicle equipped with front outboard seat belt systems that have been evaluated in accordance with the front seat belt fit criteria.

5.2 BTD

On a case-by-case basis, and upon request by Transport Canada, the Manufacturer will identify which method was used to evaluate front seat belt fit for an Applicable Vehicle, (i.e. the eBTD , an alternative software to the eBTD or the physical BTD).

5.3 Reports

The manufacturer will supply the appropriate supporting data for the evaluation, as specified in the sample reports attached (Appendix A: Sample eBTD Report, Appendix B: Sample BTD Report).

 

 

Addendum 2 Belt-fit Test Device Training

 

 

1. Introduction

This section describes the minimum requirements for electronic Belt-fit Test Device ( eBTD ) and physical Belt-fit Test Device (BTD) training to ensure a high level of skill in developing a belt fit model.

2. eBTD Training

eBTD training shall consist of:

  • Hands-on project type modeling projects.
  • Tips and techniques to handle different simulation scenarios.
  • Troubleshooting of potential error sources.
  • Specific OEM supplied projects.

Training shall be held such that, after successfully completing the course, the participants can operate the eBTD software independently, i.e. obtain all information necessary to define the model, understand the simulation methodology and correctly assess the simulation results.

2.1 eBTD Course Contents

The eBTD training course shall address the following topics:

  • Background information on the simulation methodology
    1. Simulation approach
    2. Range of application and limitations
  • Working with the Graphical User Interface (GUI), the eBTD software in typical hands-on examples that cover:
    1. Starting and closing the program
    2. File handling capabilities
    3. Manipulating views
    4. Menu bars, shortcut buttons, pull-down menus, etc.
    5. View menu, handling the 3D workspace: zooming in and out, clipping areas, layers, etc.
  • Creating and positioning an eBTD manikin
    1. Obtaining necessary input information
    2. Creating an eBTD manikin
    3. Animating the eBTD manikin in the correct position in different configurations.
  • Defining anchor kinematics
    1. Choose correct anchor class
    2. Obtaining necessary input information
    3. Defining anchor kinematics geometry
    4. Defining anchor movement limitations
    5. Measuring stiffness parameters
    6. Defining stiffness parameters
  • Defining seat belt parameters:
    1. Obtaining necessary input information
    2. Define belt width
    3. Define retractor force
  • Dealing with collision control
    1. Obtaining necessary input information
    2. Define collision objects
  • Calculating the seat belt routing
    1. Check feasibility of defined simulation scenario
    2. Runtime calculations
  • Interpreting the results
    1. Check feasibility of results on:
      • Belt routing
      • Anchor kinematics
      • Collision
    2. Interpret pass/fail criteria:
      • Scale values
      • Offsets

During the course, examples shall be used to demonstrate the above features. Participants shall repeat the examples independently and finally shall be able to create their own simulation scenarios.

2.2 eBTD Training Material

Training material shall consist of the following:

  • Training manual
  • Sample data sets
  • Software manual

The training manual shall address the software features listed above in such a way that it is possible for a trainee to work through the manual independently and apply the documented samples and descriptions to the accompanying sample data sets. For more detailed information and as reference material, the software manual shall be included.

3. Physical BTD Training

This section describes the minimum requirements for BTD training to ensure that the BTD can be installed into a vehicle in a repeatable and consistent manner and that the seatbelt can be properly deployed. The measured belt fit scores resulting from an installation shall satisfy the requirements contained herein.

Training shall consist of:

  • Hands-on experience with the physical BTD,
  • Troubleshooting BTD/vehicle interference issues,
  • Belt-routing guidelines,
  • Tips and techniques to handle belt fouling,
  • Instructions for score and offset measurements.

Upon successful completion of the training, participants will be able to complete the BTD installation independently, including belt routing, score measurement and trial repetitions.

3.1 BTD Course Contents

The BTD training course shall address the following topics:

  • Background information on BTD methodology
    1. Positioning approach
    2. Range of application and limitations
  • Introduction to the physical mannequin
    1. Review of SAE J826 – BTD conversion kit
    2. Assembly of BTD manikin
  • Vehicle Preparation
    1. Stabilizing the vehicle
    2. Marking and measuring vehicle components
    3. Initial position of seat and other items
  • Manikin Installation (first seat)
    1. Placing manikin in vehicle
    2. Positioning legs and feet
    3. Installing weights
    4. Attaching lap and torso forms
    5. Positioning manikin
    6. Comments on rear seat installation
  • Belt Deployment
    1. Draping the belt for initial position
    2. Using a belt tensioning device
    3. Re-deployment techniques
    4. Actions for belt fouling
  • Belt Score Measurements
    1. Recording seat back and pan angles
    2. Reading scale scores
    3. Measuring belt offset
    4. Method for repeated trials
  • Anchorage Measurements (Time Permitting)
    1. Typical measurement techniques for defining anchorages
    2. Implementation of measurements for eBTD use

3.2 BTD Training Material

The following material will be provided:

  • SAE J826 - BTD Conversion Manual
  • BTD Installation Procedure
  • Data Record Sheets

Curriculum will focus on using the BTD in accordance with the installation procedure.

4. Training Certificate

Upon successful completion of either the eBTD or BTD training course, participants shall receive a Certificate of Accreditation.

 

 

ADDENDUM 3

 

 

PARTICIPATING VEHICLE MANUFACTURERS

BMW CANADA INC.

DAIMLERCHRYSLER CANADA INC.

FORD MOTOR COMPANY OF CANADA, LIMITED INCLUDING JAGUAR CANADA AND LAND ROVER CANADA, DIVISIONS OF FORD MOTOR COMPANY OF CANADA, LIMITED

GENERAL MOTORS OF CANADA LIMITED

HONDA CANADA INC.

HYUNDAI AUTO CANADA

KIA MOTORS CANADA INC.

MAZDA CANADA INC.

MERCEDES-BENZ CANADA INC.

MITSUBISHI MOTOR SALES OF CANADA INC.

NISSAN CANADA INC.

PORSCHE CARS CANADA LTD.

SUBARU CANADA INC.

SUZUKI CANADA INC.

TOYOTA CANADA INC.

VOLKSWAGEN CANADA INC.

VOLVO CARS OF CANADA LTD.

 

 

1 SAE 2003-01-1353
The Role of Nondeterminism in Verification and Validation of Computational Solid Mechanics Models

 

 

2 Section 3.4.6.5 of the Technical Framework Agreement Biokinetics report # R04-05, 2004-03-11

3 Force-Deflection Measurement Procedure for eBTD Stiffness - B2 Anchorage -Report No.:D04-02-2004-08-12

4 ibid

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