Aspirated Airbag System Performance

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Aspirated Airbag System Performance

• P. Barry Butler

2
Acknowledgements

• TRW Vehicle Safety Systems, Inc.
• General Motors Corporation
• Professor L.D. Chen
• Peter W. Green, Ph.D.

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Presentation Overview

• Background
• System Components
• Gas Generator Requirements
• Recent Work - Aspirated Modules
• Full-scale hot firings
• Scaled (1/6) model cold firings
• Computational simulation
• Current Trends/Challenges

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Background - System Components

• Gas Generator
• Solid propellant gas generators
• Hybrid gas generators
• Stored gas
• Combustible gas
• Multi-stage
• Canister
• Bag

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Background - Gas Generator Requirements

• Stability
• Safety
• Gas temperature
• Product gas composition
• Fast delivery of gas
• Volumes up to 150 Liters
• Delivery times below 60 ms
• Compact storage
• Consistent output from -50 F to 150 F
• Long-term viability (gt 20 years)

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Aspirating Airbag
Bag
Canister
Inflator
Screen
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Aspirating Airbag Module
Canister
Airbag
Airbag
Solid wall
Perforated plate
Gas generator
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Background - Aspirated Airbags
Conventional Airbag

• Aspiration flow rate is dependant on the
  gas-generator, mass-flow properties
• Traditional evaluation methods for mass-flow rate
  into the bag will not directly apply.

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mgg
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Aspirating Airbag
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Specific Objectives

• Understanding key factors of the aspiration
  process
• Limits of entrainment
• Absolute upper limit (unconfined jet)
• Practical upper limit
• Effects of confinement
• Key design parameters of canister
• The airbag as a moving boundary
• Effects of downstream moving boundary
• Impingement and transition
• Develop a first-order aspiration flow-rate model
  which accounts for the gross features of the flow

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Methodology

• Aspiration mass-flow
• Volumetric-flow rate
• Density
• Temperature
• Airbag action
• Location of the airbag
• Velocity of the airbag
• Volume of the airbag
• Growth rate of the airbag

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Test Facilities and Simulation Tools

• Hot-Firing Test Apparatus
• Cold-Firing Test Apparatus
• Simulation Tools
• CFD-ACE
• AIM
• ISP

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Aspirating Airbag Module
Canister
Airbag
Airbag
Solid wall
Perforated plate
Gas generator
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System Flow Network
Transient Volume Bag
SPGG
Canister
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mslag
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Solid Propellant Gas Generator

• Sodium Azide based
• 1200 K flame temp.
• 40 conversion to gas
• Predetermined mass-production history
• Sonic exit condition
• underexpanded exhaust
• Screens required for cooling and slag collection

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Cold-Firing Test Apparatus
Automatic Positioners
Pressure Regulator
N2
PC
1/6 Scale Nozzle Cartridge
Anemometer
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1/6 Scale SPGG Jet Visualization

• Jet is sonic at exit
• Jet is underexpanded

Single jet
Multiple jets
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CFD Modeling

• Validation of the CFD Modeling

a. Shadowgraph image of a single jet at pressure
of 400psi
b. Mach number profile from Fluent modeling
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CFD Modeling

• CFD Modeling of the Entrainment

Velocity vectors of the flows
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Canister
Canister

• Modifications to the mass flow entering the bag
  must be made here.
• The only difference between standard units and
  aspirating units is in the canister.
• Key to the aspiration effects

Mixture T(t,etc)
N2 500 K
Mixture T(t, etc...)
Air 298 K
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Hot-Firing Test Appartus
Bag
Hood
Aspiration Tube
Hot-wire Anemometer
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Entrainment Example
Break-out
27 g Aspirated gas
16 g Outflow
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Airbag

• The moving boundary
• Packing Resistance
• Travel
• Filling characteristics
• Tethers
• Venting
• Vent holes
• Fabric
• Canister

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Deployment Sequence
Entrainment
Mass Flow
Venting
Impingement
Breakout
Time
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Methodology - Example
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Baseline Summary

• Net positive aspiration
• Reduced aggressiveness

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Results Baseline-Free Comparison

• Airbag-aspiration dependency
• Airbag causes loss of mass from system initially
• Airbag causes amplification of aspiration
• Jet entrainment doesn't capture aspiration flow
  profile

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Results Weighted Pendulum

• Pendulum
• Net loss of mass
• Doesn't increase outflow
• Reduces inflow signifanctly

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Background - Current Trends/Challenges

• Sensors
• multiple operating thresholds
• seat belt use (yes/no)
• weight
• occupant position
• roll rate
• Propellant Formulations
• non-azide
• product gas

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Background - Current Trends/Challenges

• Tailored performance
• address multiple operating conditions
• out of position (OOP)
• non-50 occupant
• belt - no belt
• Seat Belt Pretensioners
• integrated with airbag
• reduce HIC
• Roll Over Protection
• Side-Impact Protection

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Background - Current Trends/Challenges

• Leg Protection
• Hood Airbag
• pedestrian impact on hood