Airbags2
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Airbags are a supplementary restraint system that inflates during a crash to prevent occupants from hitting the vehicle's interior. The three main components are the airbag module, diagnostic unit, and crash sensors. The airbag module contains the airbag and inflator unit. The diagnostic unit monitors readiness and the sensors detect crashes over 8 mph to trigger deployment. Advanced smart restraint systems adapt deployment based on crash details and occupants detected through various sensors.
Airbags2
- 1. Airbags
- 2. Supplementary Restraint System for driver and/or passenger safety in case of a crash. Basic Mechanism: A thin nylon bag in the steering wheel / above glove compartment inflates in the event of an impact and prevents the driver/passenger from hitting the steering wheel/dashboard. 3 Main Components: 1) Airbag module 2) Diagnostic Unit 3) Crash sensors What are Airbags?
- 3. Airbag Module Contains both inflator unit and light-weight fabric airbag and is located either inside: 1) Steering wheel hub 2) Above glove compartment 3) Near side compartment (as separate/combined head/side/window-curtain airbag) Airbag: Thin nylon fabric bag folded neatly into steering wheel that inflates to the size of a large beach ball on impact. Inflator unit: Contains a number of sodium azide pellets which are electrically ignited to produce N2 that then fills the airbag. This is preferred to storing compressed gas in the unit (space, durability) Both airbag and inflator unit are for single deployment only ie have to be replaced after a crash
- 4. Diagnostic Unit Enables inflator unit and sensors when vehicle is turned on, performs self check. Constantly monitors airbag readiness and indicates malfunctioning through an indicator on dashboard Usually stores electricity to activate airbag in the event that a crash damages the battery / link to battery Sensors Several crash sensors located in the front of vehicle and in the passenger compartment Each senses the sudden deceleration or impact in the event of a crash and flips a mechanical switch to indicate a crash.
- 5. Frontal crash scenario: Car crashes into an obstacle (wall) at 20+ mph Sensors detect the deceleration and inflator unit activated Deployment sensitivity: To guard against accidental inflation on hard braking, sensors detect collisions into a solid barrier at speeds greater than 8-14 mph only as impacts An electric current is used to heat a filament wire that ignites the NaN3 capsules, producing N2: 2NaN3 2Na + 3N2 10Na + 2KNO3K2O + 5Na2O+ N2 K2O + Na2O SiO2 alkaline glass (safe, unignitable) 130 g of NaN3 produces 67 ltrs of Na Airbag Deployment
- 6. Airbag Deployment The airbag then inflates fully at speeds > 320mph within 0.05s of crash. For maximum safety, occupant must have seat belt on and sit with chest 10 from steering wheel Immediately after full inflation, the airbag deflates through tiny pores on the surface within 0.3s Accelerometer
- 7. An on/off switch Combination with seat-belt pre-tensioners and other safety systems Inflation in the event of fire (high temp.) to prevent explosion of solid compound Depowering and differential powering Small rapid deployment airbags for side impact at roof-rail or door or seat back. eg: 1) Beltline Head/Torso Side Airbag 2) Inflatable Tubular Structure Additional Features
- 9. Fluid pressure based weight sensors
- 10. Smart Restraint System Is one that adapts its geometry, performance or behavior to suit varying impact types and/or occupants & occ. posns. Must be able to distinguish between: RFIS & child seat Child Adult Empty Subsets of possible seating posns. for above (< / >10) Belted / non-belted Crash severity Crash direction ie, a smart restraint system must be able to update itself on the following: Occ. characterisation Occ. location Accordingly decides: Which airbags to deploy when Full blown / supressed Seat belt pre-tensioning, retraction/collapse of parts Direction of deployment Sequencing & Timing Post deployment action
- 11. Smart Restraints Detection types: mechanical spatial other Means of detection: Weight & distribution (3) Seat belt (webbing , rotation ctr & buckle) Active Infra-red (OOP sense) Ultrasonic Radar/Microwave Capacitive tags for RFIS & smart keys Height sensors in seat / belt Advance meth. (complex, high computing power reqd.) Passive Infra-red Video systems Biometric sensing Systems must: Sequence & time appropriately Extremely reliable Work within varying auto interior atmosphere and lighting Differentiate camouflage Low cost
- 12. Smart Restraints Components Side/Variable/dual-stage airbags Seat-belt pre-tensioners Side/Central/Satellite/Safing crash sensors Occupant sensors Central ECU Pre-crash sensors Driving states: Normal Collision avoidable Collision imminent Post-crash Sensor types: Electromechanical Accelerometers Pressure Stress-wave Pre-crash Pre-crash sensing More details reqd from sensors Advantage: Enables early decision and pre-tensioning Disadv: imprecise object classification & cost Same sensors as those for ACC, CW/CA