Linear Impactor Performance Characteristics for Ejection Mitigation Testing

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Linear Impactor Performance Characteristics for
Ejection Mitigation Testing

• Douglas Stein
• Autoliv, AORC

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Objective

• Determine range in variability between current
  impactors used for Ejection Mitigation Testing
• Determine the affect these variables have on test
  results
• Provide basis for establishing impactor
  performance specifications

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Ejection Mitigation Test (NHTSA)
Negative Excursion
Positive Excursion
Zero Excursion (Inside surface of side window)
18 kg Featureless Headform mass
Excursion Performance Criteria not yet published
by the NHTSA (100,150, 200mm?)
Door
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Ejection Mitigation Test (NHTSA)
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Ejection Mitigation Test (400J)
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Factors of Test Variability

• Vehicle trim variations
• Vehicle manufacturing variability
• Test variability due to
• Velocity tolerance
• Displacement measurement accuracy
• Impactor bearing friction
• Headform skin/RRAB friction
• Headform skin stiffness (not specified)
• Impactor shaft radial deflection
• Delay time between firing the impactor and
  contact

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Factors of Test Variability

• Able Now to Characterize
• Velocity tolerance
• Displacement measurement accuracy
• Impactor bearing friction
• Headform skin/RRAB friction
• Headform skin stiffness (not specified)
• Impactor shaft radial deflection
• Delay time between firing the impactor and
  contact

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Bearing Friction and Radial Deflection
Measurements
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Timing and Repeatability Measurements
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Data Compiled from 8 Impactors
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Data Compiled from 8 Impactors
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Sensitivity to Bearing Friction

• Impactor shaft friction (in linear guide) can
  absorb Kinetic energy that would otherwise be
  directed into the restraint system especially
  where high radial loading is present.
• On equipment considered in this study, the
  friction coefficient varies from 0.17 to as much
  as 2.62 (average is about 0.35)

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Sensitivity to Bearing Friction
Radial load measured from actual 400J containment
test Example 1 First Row Upper Rear
Example of Low Radial force as a percentage of
Axial Force
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Sensitivity to Bearing Friction
Example 1 First Row Upper Rear
292J
U(2.62)105J (26)
U(0.35)14J (4.5)
U(0.17)6.8J (2.3)
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Sensitivity to Bearing Friction
Example 1 First Row Upper Rear
-26 22mm less excursion -6 4mm less
excursion -2 2mm less excursion
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Sensitivity to Bearing Friction
A follow-up test series (6 tests) using
impactors having friction coefficients 2.62, and
0.17 showed an increase in excursion of 20mm with
the lower friction coefficient!
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Sensitivity to Bearing Friction
Radial load measured from actual 400J containment
test Example 2 First Row Lower Rear -
secondary
U(2.62)270J (59)
U(0.35)38J (17)
U(0.17)18J (9)
Example of High Radial force As percentage of
axial force
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Sensitivity to Bearing Friction
Example 2 First Row Lower Rear - secondary
-59 192mm less excursion -17 70mm less
excursion -9 35mm less excursion
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Sensitivity to Shaft Deflection

• Impactor shaft deflection can allow the headform
  to deflect away from radial loads. This could
  result in greater excursion.
• Only one impactor showed shaft deflection greater
  than 12mm (25mm with only 27kg added).
• Still waiting for CAE analysis to determine the
  affect on excursion but expected to be minimal
  for small deflections (lt10mm).

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Sensitivity to Timing
Effects of impactor delay time on bag pressure
Actual press/time varies with inflator
performance, airbag volume, fabric coating, etc
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Summary
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Next Steps

• Select correlated CAE model of a containment IC
• Run a virtual DOE to evaluate the effects of the
  measured variables on excursion (using the
  measured range in variability as limits)
• Validate results with containment tests
• Define performance requirements for the impactor
  based on DOE findings
• Provide data to NHTSA for use in Occupant
  Ejection Mitigation test plan
• Friction between headform skin and the airbag
  have not yet been addressed

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THE END
Questions?