The Effect of a Wheelchair Integrated Occupant Restraint System on Wheelchair Tie-down and Occupant Restraint Design Characteristics

Linda van Roosmalen PhD
Gina E Bertocci PhD

Slide 1
The Effect of a Wheelchair Integrated Occupant Restraint System on Wheelchair Tie-down and Occupant Restraint Design Characteristics

Linda van Roosmalen PhD
Gina E Bertocci PhD

Slide 2
Occupant Restraint Deficiencies Summary

ORS are used for:

• Varying size users
• Varying wheelchair designs and dimensions
• Varying vehicle structure

FWORS use could result in:

• Poor restraint fit for a-typical users
• Reduced user comfort - Reduced usage
• Restraint related injuries during impact
• Increased risk of occupant injury during impact

From the occupant restraint survey, observation and belt fit study and the literature, the problem can be stated as follows.

FWORS are ineffective due to: varying occupant population and wheelchair designs and dimensions.

Varying location of the wheelchair in the securement zone.

Interference with wheelchair armrests, lap trays etc. and interference of the vehicle structure with restraint anchor installation.

Also, the use of FWORS appears to result in compromised belt fit for a varying occupant population, reduced user comfort, which may also cause individuals not to use restraints.

Finally, belts touching the neck or other soft areas may result in restraint related injuries during impact. And poorly positioned belts could cause occupant injury due to excessive forward movement of the occupant, or due to increased loads onto body parts such as the abdomen, chest and head.

Slide 3
Research Objective

To improve the safety and comfort of wheelchair Occupant Restraint Systems (ORS) when used in transportation

Wheelchairs are designed to provide mobility to individuals. Since many wheelchair users use their wheelchairs as motor vehicle seats, there is a growing demand for wheelchairs that can be safely used in transportation.

This means that design criteria need to be established for wheelchairs and occupant restraint systems. Design criteria in the areas of crash protection, seat design characteristics, usability and comfort.

This all needs to be done to provide individuals using a wheelchair comparable level of safety and user comfort as individuals seated in an original equipped and manufactured (OEM) vehicle seat and restraint system when exposed to crash conditions.

Graphic Description: a diagram with four arrows pointing from a picture of a wheelchair with occupant restraint system towards crash protection, usability, seat design and comfort.

Slide 4
Seat Integrated Restraint Advantages

Restraint effectiveness
Early crash participation/protection
Decreased torso rotation
Pelvic and shoulder belt anchors on the seat:

• Eliminates incorrect adjustment
• Optimizes belt geometry and user comfort
• Increases acceptance level of belt
• Improves ease of handling of the occupant restraint
• Improves protection in all incident situation

(Haberl et al. @ BMW, Germany, 1989; Wainwright et al., 1994;

Cremer, 1986; Ruter & Hontschik @ Batelle Ins. Germany, 1979)

Slide 5
Plan of Study

Prototype wheelchair integrated occupant restraint system (FEA)

Evaluate seat to back strength of wheelchair seating system (FMVSS 207)

Evaluate strength of seat belt anchors of a concept WIRS (FMVSS 210)

Evaluate capability of seating system and WIRS to withstand occupant restraint loads (WC-19)

Evaluate occupant safety (SAE J2249)

Optimize WIRS characteristics using computer simulation

Slide 6
Concept WIRS

Graphic Description: two pictures: one picture shows a solid model with loads at the bottom and top of the wheelchair integrated restraint structure. This solid model is used to run Finite Element Analysis. The other picture shows the actual prototype of the wheelchair integrated restraint system that was used for dynamic crash testing.

Slide 7
Concept WIRS

Graphic Description: front and rear view photographs of the WIRS on the surrogate wheelchair base used for dynamic sled testing.

Slide 8
Sled Impact Test

Evaluating the seating system and occupant safety:

Dynamic Sled Impact Setup (20g/30mph)

Hybrid III 50th % male dummy (172.3lb)

Surrogate belt type wheelchair tie-down system

Wheelchair is secured with four point tiedown

WIRS versus fixed vehicle mounted ORS

Compliance with Wheelchair 19 Standard

Compliance with SAE J2249 and GM IARV’s

Slide 9
Dynamic Evaluation?
Test Setup

FWORS: Fixed Wheelchair Occupant Restraint System

Graphic Description: the FWORS picture shows the setup of the wheelchair and occupant restraint system. The occupant restraint system is attached to the exterior. A Hybrid III ATD is restrained by the FWORS

WIRS: Wheelchair Integrated Occupant Restraint System

Graphic Description: the WIRS picture shows the test setup of the wheelchair and occupant restraint system that is attached to the wheelchair itsself. A Hybrid III dummie is restrained by the WIRS.

Slide 10
Dynamic Evaluation FWORS Test Setup

Upper torso restraint location according to SAE J2249

Graphic Description: One picture is a drawing showing the side front and top view of a 50th percentile male wheelchair occupant seated in a wheelchair. This picture was taken from the SAE J2249 standard. It shows the optimal location of the shoulder belt anchor. The optimal anchor location is positioned 300 mm behind the shoulder, 173 mm above the shoulder and 300 mm from the centerline of the body.

WCSS on surrogate base

Graphic Description: the other picture is a photograph showing the surrogate base with the wheelchair seating system attached to it.

Slide 11
FWORS Test Setup

Graphic Description: two photographs showing the test setup of the fixed vehicle mounted occupant restraint system and the wheelchair that is secured with a 4-point tiedown system to the sled platform. An instrumented hybrid III dummy of a 50th percentile male is seated in the wheelchair and is restrained by a upper torso and pelvic belt which are attached to the sled platform and vertical post.

Slide 12
Dynamic Evaluation FWORS

Graphic Description: a picture showing an actual video of sled impact test during frontal impact (30mph/20g).

Slide 13
Dynamic Evaluation WIRS Test Setup

Upper torso restraint anchor according to SAE J2249 and WCSS on surrogate base

Graphic Description: a picture showing the optimal upper torso restraint angle for a 50th percentile male as is used to determine the anchor location of the wheelchair mounted occupant restraint system which is shown in another picture on this slide. This wheelchair mounted occupant restraint system existing of a shoulder and pelvic belt is attached to a wheelchair seating system, which is again attached to the surrogate

Slide 14
WIRS Test Setup

Graphic Description: two photographs showing the test setup of the wheelchair mounted occupant restraint system and the wheelchair that is secured with a 4-point tiedown system to the sled platform. An instrumented hybrid III dummy of a 50th percentile male is seated in the wheelchair and is restrained by an upper torso and pelvic belt which are attached to the wheelchair seat frame.

Slide 15
Dynamic Evaluation WIRS

Graphic Description: picture showing an actual video of sled impact test during frontal impact (30mph/20g).

Slide 16
Dynamic Comparison

Vehicle Mounted Restraint System and Wheelchair Mounted Restraint System

Graphic Description: a comparison of the two videos of the two different systems.

Slide 17

Graphic Description: This picture shows three screenshots of the moving dummy during frontal impact at 40, 80 and 120 milliseconds for the two different restraint scenarios.

Slide 18
Dynamic Evaluation Motion Comparison

Head (forward) excursion [SAE limit = 25.6 cm]

Knee (forward) excursion [SAE limit= 14.8 cm]

Graphic Description: Two graphs of the motion comparison of the two restraint scenarios: forward head excursion and forward knee excursion. Slide 20 will give a numerical overview of the differences between the two restraint scenarios.

Slide 19
Dynamic Evaluation Motion Comparison

Wheelchair (forward) excursion [SAE limit = 7.9 cm)

Graphic Description: graph of the forward wheelchair excursion. Slide 20 will give a numerical overview of the differences between the two restraint scenarios.

Slide 20
Dynamic Evaluation

Graphic Description: a table consisting of five columns:
1. description of value
2. % difference between FWORS and WIRS values
3. FWORS scenario values
4. WIRS scenario values
5. General Motors and SAE limits

There are 13 rows consisting of the following descriptions:
1. total mass (wheelchair weight plus test dummy weight plus seating system weight)
[%diff =0.4 FWORS=180 lb WIRS=210 lb]

2. head injury criteria value
[%diff=0.2 FWORS=446.7 WIRS=257.3 max GM-SAE value=1000]

3. sternum compression
[%diff=0.2 FWORS=1.94 inch WIRS= 1.61 inch max GM-SAE value=3inch]

4. maximum upper torso restraint load
[%diff=0.1 FWORS=2361 lb WIRS=2024 lb

5. maximum pelvic restraint load
[%diff=0.2 FWORS=3142 lb WIRS=2449 lb

6. wheelchair tiedown load

Slide 21
Comparison

Chest acceleration

Graphic Description:

Mid sternum compression

Graphic Description: a graph of the Chest acceleration and a graph of mid sternum compression. The previous slide, Slide 20, gives a numerical overview of the differences between the two restraint scenarios.

Slide 22
Comparison

Pelvic restraint load

Upper torso restraint load

Wheelchair Tiedown Loads

Graphic Description: graphs of the pelvic restraint load, upper torso restraint load and wheelchair tiedown loads for the two different restraint scenarios. Slide 20 gives a numerical overview of the differences between the two restraint scenarios.

Slide 23
Comparison

Neck Flexion (C1 level)[GM/SAE limit = 1681 in-lb]

Neck axial load (tensile)[GM/SAE limit = 652 lb.<35ms]

Neck shear force (fore/aft)[GM/SAE limit = 337 lb.<25ms]

Graphic Description: graphs of the neck flexion, neck axial load and neck shear force of both restrain scenarios during frontal impact over 120 milliseconds. Slide 20 gives a numerical overview of the differences between the two restraint scenarios.

Slide 24
Dynamic Evaluation Conclusions

WIRS and FWORS compliance

• GM-IARV occupant injury criteria
• SAE J2249 excursion criteria
• WIRS feasibility
  

Additional testing

• Study seat and restraint characteristics to improve head accelerations and neck loads/moments for WIRS scenario
• Validity of test results
• Compare WIRS with ‘real-world’ FWORS scenarios with less than optimal belt fit
  

Slide 25
Future Steps

• Build and evaluate a computer simulation model using sled impact test data
• Usability of WIRS
• Effect of WIRS on seat structure
• Study restraint characteristics
• Optimize wheelchair seat design criteria
  

Slide 26
Acknowledgements

This study is supported through:

• NIH-STTR Grant
• NIDRR: RERC on Wheeled Mobility
  

Slide 27
Thank You For Your Attention

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Updated: March 14, 2002