Supplemental Restraint Systems

Supplemental Restraint Systems

Safety Statement

Information and Administration: The course will start at 9.00am and finish at 5:00pm. Lunch and refreshments will be provided at the times advised by the training instructor. Workshop Safety • It will be expected that all necessary workshop health and safety procedures are followed e.g. the wearing of suitable work wear, safety footwear, eye and ear protection when in the workshops is mandatory. We recommend that barrier cream and workshop gloves are used at all times. • Ensure that you are fully aware of the emergency stop procedure for any of the rotating equipment used during the course. While working on rotary test equipment or engines, please ensure that all loose clothing is secure and can not get caught in the equipment or engine parts.

Objectives

• Technicians will be able to identify the various components of SRS systems • Technicians will be able to work safely around SRS systems • Technicians will be able to disable and enable SRS systems for repair or replacement

Introduction

Fire Escape Smoking Areas Toilets Mobile Phone, please switch off or on silent

Group introductions…..

Introduction

Airbag technology has been developed to cushion occupants from more areas of the vehicle and increase safety in a crash.

From an extrication perspective, new technology creates a new layer of challenges for the rescue services, although there are developments that reduce the likelihood of somebody being harmed in a rescue scenario. We will look at some of theses interesting developments and see why they are being introduced.

Important Information

Serious injury or death can be a result of improper removal/installation techniques.

Follow manufacturer’s instructions for disabling Supplementary Restraint Systems Prior to working on any airbag component. Airbags are dangerous and a powerful safety system which should no be taken lightly or tampered with. If you are not a qualified/certified technician, seek the help of a professional to service the airbag systems.

Always disconnect the battery and wait manufacturers specified time before working on any airbag system.

Important Information

To disable the airbag system, be aware of the following, this is typical procedure:

• Wear safety glasses when servicing the air bag system • Always disconnect the battery negative, isolate the cable end and wait the allotted time given by the vehicle manufacturer before proceeding with any necessary repair or service. Failure to observe this precaution may cause accidental air bag deployment and personal injury.

Introduction

Supplemental Restraint Systems (SRSs) are also called airbag systems. An airbag is a balloon-type passenger safety device that inflates automatically on vehicle impact. Original systems were designed to protect only the driver. In addition, the airbags inflated only if there was sufficient impact at the front of the vehicle. Modern systems also protect the passengers. They can be triggered by side as well as frontal impacts. Airbag systems are intended to be used with seat belt restraints. An unbelted driver or passenger is not likely to receive maximum protection for the airbag. Unbelted occupants have been seriously injured or killed by inflating bags.

SRS components

1. Drivers Airbag 2. Passenger Airbag 3. Side Airbag 4. Curtain Airbag 5. Knee Airbag 6. Clock Spring/Spiral Cable 7. Airbag Control Module 8. Crash/Impact Sensor 9. Pre-Tensioner 10.Occupancy Detection System

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SRS Components

Airbag Terminology Airbag system

Whole airbag system including components, wiring and airbag control module. The clock spring or spiral cable allows the relevant control unit to communicate with the steering wheel electronics.

Clock spring

ECU/ACM The airbag control module manages the airbag system; it continuously looks for faults and will illuminate the airbag MIL if it detects one. It is also responsible for the deployment of airbags in an accident situation. Crash/Impact Sensor Small sensors located on the car which detect & then

inform the airbag module of an impact to allow it to decide which components need to be deployed, if any.

Airbag Terminology

Pre-tensioner

Seatbelt pre-tensioner either fitted to the seatbelt reel or buckle.

Inner pre-tensioner

Seatbelt pre-tensioner on the buckles.

Outer pre-tensioner

Seatbelt pre-tensioner in the reels or on the inner sills. Seatbelt pre-tensioner on the inner sills, buckles or rear inner buckles.

Lap belt pre-tensioner

Curtain airbag

Airbag in the roof lining

Knee airbag

Airbag under the steering column or glovebox

Drivers airbag

Steering wheel airbag

Passenger airbag

Dashboard airbag

Airbag Terminology

Side airbag

Seat or door airbag.

L.H or R.H airbag

This can refer to the left hand or right hand and can refer to the side airbag or frontal airbags depending on vehicle manufacturer so don’t get caught out. System used to detect where passengers are located within the vehicle.

Occupancy Detection

Squib

Heating element used to ignite the gas generating material.

Inflator Module

Inflation assembly for airbag activation.

SRS MIL

Malfunction indicator lamp (airbag light).

Clock Spring/Spiral Cable The clock spring is simply a coil that retracts and expands inside its housing as the steering wheel turns. Its function is to maintain electrical continuity for all the components on the driver's airbag. The

components include the airbag, horn, and any vehicle controls such as radio, cruise, heat and even telephone on some vehicles.

Airbag Control Module

The (ACM) Airbag Control Module is a small computer module on a vehicle that determines when and which airbags to deploy in the event of an accident. It monitors data from multiple crash sensors around the vehicle and decides

if the crash impact requires a deployment of the airbags.

Crash/Impact Sensor

There are several types of sensors.

The crash sensors can be mounted directly on the SRS control unit and mounted in the front, side and rear of the vehicle. These sensors measure accelerations or other variables, such as the pressure inside the door and pass these variables to the SRS control unit.

Pre-Tensioner

A pretensioner, is a device designed to make seatbelts even more effective by removing the slack from a seatbelt as soon as an accident is detected or if the system senses excessive seatbelt tension on the driver or passenger’s seatbelt.

Drivers Airbag

Stored in the steering wheel and designed to inflate in less than 1 second after registering a significant impact to help stop the driver hitting the steering wheel – can be single or dual stage.

Front Passenger Airbag

Stored in the passenger dashboard and designed to inflate in unison with the driver's side airbag if required; prevents passenger from impacting the dash or windcreen.

Side Airbag

Usually stored in the vehicle seat or door card, it inflates between the passenger/driver and the door to protect the persons shoulder to torso area.

Side/Rear Curtain Airbag Designed as a head protection from side impact collisions and rollovers; these airbags deploy

from the roof of the vehicle. Rear curtain is deployed from the roof of the vehicle behind the passenger seats, to protect the necks of the rear seat passengers.

Knee Airbag

As the name suggests, this airbag protects the passenger’s knees by deploying under the dash or from the rear of the front seats to absorb the impact during a head on collision.

Seatbelt Airbag

Currently just an optional airbag, the seatbelt airbag inflates the seat belt where it contacts the body to protect the chest and ribs in a head on collision

External Airbags

Side crashes currently account for around 37-40 per cent of car accidents. External airbags that pop up on the side of cars within 30 milliseconds could be available before the end of the next decade. The bags deploy from the sill beneath the doors. Engineers are now working on radar and camera systems to manage this.

How Do SRS Components Work

Frontal Impact

SRS; what happens in a frontal impact?

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Side Impact

SRS; what happens in a side impact?

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How Airbag Systems Work

The airbag control module (ACM) is the ‘brains’ of the system, to tell each airbag when to deploy. This is done by connecting an array of sensors in the front, back and sides of the vehicle to register when an impact occurs. When one or more of these sensors signal the ACM that the safety parameters have been crossed, the air bag control unit signals a one to three-amp current pulse to ignite a conductor that has been wrapped in combustible material. The ignition triggers the gas generator to deploy the airbags, this all happens in approximately 15 to 30 milliseconds.

How Airbag Systems Work The first step in deploying an airbag is for the system to realise that a crash has occurred. This is accomplished by crash sensors, there are many different types of sensors. The earlier less complex sensors were simply mounted near the bottom of the radiator support, at the front of the vehicle, this area is respectfully known as the crash zone. The more complex sensors, called Micro-Machined Accelerometers are mounted inside the ACM and around the vehicle. These measure the speed and severity of the crash

How Airbag Systems Work To prevent airbag deployment in small accidents, the ACM can not deploy an airbag from one signal. The ACM must receive two or more impulses to deploy an airbag. This second impulse comes from the safety or arming sensor. This sensor is usually mounted inside the vehicle and must experience a sudden deceleration like the crash sensor. Closing of the safety or arming sensor provides power to the inflator module via the ACM. The ground is provided through the activation of a crash/impact sensor via the ACM. Hence the above statement, two sensors are required to active an airbag deployment sequence.

Mass-Type Sensor An impact sensor is normally fitted to the front of the vehicle as this is where a collision is likely to occur. The sensor is positioned inside the engine bay and a similar safety sensor is located inside the passenger zone of the vehicle. This safety sensor is required to measure the intensity of the collision to determine whether the impact is over a certain threshold to justify the release of an airbag. The sensors work on the principle of detecting a decrease in acceleration of a moving vehicle and generating an electrical impulse.

Mass-Type Sensor

During a collision, the sensing mass is forced forward into the gold-plated contacts as a result of the change in the state of motion. Following the movement of this metal ball into the contacts, this metal mass makes contact with the electrical terminals at either side of the metal ball which alerts the central unit of a collision (i.e. the electrical contact completes the circuit).

Roller-Type Sensor The roller-type sensor consists of a weight connected to a coil spring component. Like the mass-type sensor, during impact with an oncoming vehicle, the metal weight is forced forward which alters the tension on the coil spring to manipulate the electrical circuit that closes off the sensor contact. It is important to note that the impact and safety sensors must activate and close off at the same time to allow for the deployment of the airbag

Airbag Control Module (ACM) Upon signal of an accident, the controller interprets the electrical input and measures the level of collision to determine the release of an airbag. In the event of one crash/impact sensor and safety/arming sensor being closed, an electrical current is transmitted to the airbag inflator assembly. Activation of the airbag results in an ignition that produces an electrical transmission between a pair of metal pins.

Crash Sensor

Airbag Inflator Assembly

Airbag

ACM

Arming Sensor

Airbag Inflator Assembly The signal from the ACM causes an electrical arc created between both pins, this activates a propellant made up of sodium azide that starts to burn as the compound decomposes to produce nitrogen gas which is passed through filters and fills the airbag.

Solid propellant charges within inflators consist of either: sodium azide with boron potassium nitrate, or nitro cellulose with nitro glycerine Gas propellant charges are a mixture of hydrogen gas with oxygen gas. Non-ignitable inert gases such as helium are also used.

Airbags The SQUIB is the heating element used to ignite the gas-generating material; it only requires 2 amperes of current to ignite the inflator. Once the inflator is ignited, the nylon bag quickly inflates (in about 30 milliseconds or 0.030) with nitrogen gas. During an accident, the driver is being thrown forward by the drivers own momentum towards the steering wheel. The strong nylon bag inflates at the same time. Personal injury is reduced by the spreading of the stopping force over the entire upper-body region.

Airbags As the explosive burns, it generates a massive amount of harmless gas (typically either nitrogen or argon) that floods into a nylon bag packed behind a cover. As the bag expands, it blows the cover off and inflates in front of the occupant. The bag is coated with a chalky substance such as talcum powder to help it unwrap smoothly. The occupant (moving towards the bag because of the impact) pushes against the bag. This makes the bag deflate as the gas it contains escapes through small holes around its edges. By the time the car stops, the bag should have completely deflated.

Airbags – Single Stage This is a single stage drivers' frontal airbag; these were the first airbags installed in vehicles.

Though they operate the same, very few look alike, each one is shaped to fit a particular steering wheel design. The inflation zone for these is 10 inches from the centre of the steering wheel to any part of the drivers body.

Airbags – Second Generation or Smart Airbags Smart airbags, is simply the name given to dual stage airbag systems; because using sensors and controls they can regulate their own deployment. One of the sensors used with the driver's frontal airbag is the seat position sensor. There are many different types of these sensors, but they all do the same thing. They measure the distance between the seat and the airbag deployment zone, or front of the steering wheel. This allows the airbag control module to deploy the airbag according to the occupant's proximity to the inflation zone.

Airbags – Dual Stage Airbag The dual-stage airbag has two inflator modules connected to one airbag. Each inflator module has a different power rating; say for example , a 70% charge in one inflator and 30% charge in the other. Depending upon conditions such as speed, crash severity, occupant seating position and seatbelt use or non-use, the airbag may deploy by firing only one of these two charges, leaving a second “live” charge. Generally, the more severe the crash, the greater chance both inflator modules will deploy in rapid succession. Some dual-stage airbags deploy both inflator modules, one after the other in every crash situation.

Airbags – Dual Stage Airbags

Frontal Airbags

Being a frontal airbag, these will only deploy in a front- end type collision.

The vehicle must be impacted either straight on, or within a 30˚ angle either side of the centre line of the vehicle

Seatbelt Pre-Tensioner The pretensioner mechanism uses an explosive charge to drive a concealed piston when sensors detect the abrupt deceleration of an accident. The piston, in turn, rapidly drives the spool around which the fabric strap of a seatbelt is wrapped. That incredibly fast retraction of the belt fabric removes the slack from the belt instantly. This extra seatbelt "pre-" tension, moments prior to the full force of impact, pulls the bodies of the driver and passengers firmly into their seats. This positions them to receive the maximum protection benefit of the airbags. It also helps prevent submarining, that's when the momentum caused by the crash jerks a victim's body under his or her lap belt and sends it careening forwards.

Seatbelt Pre-Tensioner

Seatbelt Pre-Tensioner

Occupancy Detection System A passenger sensing system is designed to help reduce the potential for inflation induced injuries or fatalities to smaller occupants, including children, who may be seated improperly in front of an active airbag. This advanced airbag system used sensors in the seat to collect information that helps the airbag computer determine whether the front- seat passenger air should inflate in a frontal crash. The sensors gather information on the occupant's weight and the type of pressure placed on the seat to help determine the correct course of deployment.

Occupancy Detection System Inside the seat, you will find a pressure sensor, a silicone-filled "bladder", and an electronic control unit (ECU). When someone sits on the seat, the pressure sensor signals the occupant's weight to the ECU. The ECU then sends that data to the airbag, which has its own control unit.

Based on that information, the vehicle's computer turns the passenger airbag on or off.

Handling

Tooling

Obviously, there is some tooling required to safely work on SRS systems and components, these include, • Multi-meter • Removal tools • Diagnostic tooling • ESD (electrostatic discharge) wrist strap

Tooling

• DMM – Digital multi meter • DVOM – Digital volt-ohm- milliammeter Used for isolating specific faults Before operating the meter, ensure you have read the operator manual Only to be used with extreme caution, Do not use for resistance testing.

Tooling

• Used to remove the airbag from the steering wheel and other locations around the vehicle

Tooling

• Diagnostic tooling • Guides you step by step through many testing procedures • Captures stored DTC’s, freeze frame, and records failures

Tooling

ESD (electrostatic discharge) wrist strap

An antistatic wrist strap, ESD wrist strap, or ground bracelet is an antistatic device used to safely ground a person working on very sensitive electronic equipment, to prevent the build-up of static electricity on their body, which can result in electrostatic discharge (ESD).

Faults

ACM/ECU defective

If you have one fault code only which relates to a defective ACM then it would appear there is something wrong with the airbag module. Sometimes they just won't accept re-programming and are deemed beyond repair

If this is the case, then you should replace your module.

Faults

If you have the fault code for a defective ACM and this is amongst other fault codes, then it could be a spurious code. Some modules do display this code until the other active faults have been rectified. This is particularly common with Hondas, Renault, Vauxhall, Peugeot and Citroen. You should work through the other fault to see if you can eliminate them. If you'd like to test the airbag module you could disconnect a known working component like a seatbelt pre-tensioner/crash sensor or airbag and it should introduce a new fault code to the modules memory, if it doesn’t and the other fault codes don’t seem to correspond to the damage or repairs then you may suspect the airbag module at fault.

Faults – Low Resistance A fault code for low resistance on a particular circuit would usually indicate a short circuit which could be caused by water ingress or a trapped or chaffed wire.

You should check the wiring for that component

Faults usually occur where people have been working or where heat has been produced by airbag deployment.

Faults – High Resistance

A fault code for high resistance on a particular circuit usually indicates an open circuit or bad connection. This could be caused by a faulty or deployed component, a connector not connected properly, damaged or trapped wiring, water ingress or corrosion in a connector or wire. The most common problem is connectors not full engaged or burnt out. Most airbag connectors can be dismantled and contain a ferrite suppressor. If the coil winding around the suppressor burns out, then the circuit will go open circuit and create high resistance.

Faults No signal fault codes usually relate to crash or impact sensors. It basically means the airbag module can not see it and this could be caused by damaged wiring or more often because the crash sensor is of the type that needs replacing after airbag deployment. Always refer to the vehicle manufacturers data for specific information.

Short-circuit usually means that the circuit in question has a short on it. Somewhere it is breached so this could be due to burnt wiring or trapped wires where something has been replaced or deployed, you should also check the connectors are connected properly.

Faults

Crash data stored – this means the module contains crash data and needs resetting or replacing.

Longitudinal acceleration threshold exceeded - this is crash data, the same as above.

Low capacitance – This usually means that the capacitance on a component is out of tolerance which can usually be put down to a faulty component or wiring.

Faults – No Communication

This means the diagnostic computer cannot establish communication with the airbag module. This could be due to in-compatible diagnostic tooling, or it could be because the module is not powered up which could be caused by a bad earth or no power feed to the module. You should ensure the ACM is bolted down with any earth straps attached and it is receiving an earth. Also check that the appropriate wire at the module is receiving battery voltage.

Basic Airbag Safety

• Serious injury may occur if airbags are accidentally deployed. • Never have your face or body directly in front of the airbag. • Never put arms through steering wheel spokes. • ESP wrist straps should be used to prevent electrical voltage deploying the airbag. • Wear safety glasses/goggles and latex gloves.

Basic Airbag Safety

• Never use memory savers when working on SRS systems. • If carrying out electric arc welding on a vehicle, always disconnect the airbags and seatbelt pre-tensioners. • Never use ohmmeter to measure the resistance of an airbag or pre-tensioner assembly. Ohmmeters create current flow in the circuits they measure, and this will deploy the bag. • Always check that all fault codes are clear after work has been completed.

Airbag Disarming The manufactures disarming procedures must always be complied with, typical procedures are, • Remove negative battery terminal • Remove airbag system fuse • Disconnect airbag connector • Allow energy reserve module to fully discharge

Airbag Disarming Work must not be started until at least 90 seconds has passed from the time when the ignition switch is turned to LOCK position and the negative (-) terminal cable is disconnected from the battery

Remember ELLE? Disconnect – Earth-Live Reconnect – Live-Earth

Handling A Deployed Airbag

Airbag powder can cause skin irritation.

Tape up airbag vent holes before removing the deployed airbag.

Vacuum passenger compartment to remove airbag powder

Carrying an Airbag

Care must be taken with un-deployed (live) airbags;

• Ensure eye protection is worn • Keep airbag facing away from the body • Do not drop or strike the airbag • Place airbag on bench with airbag pointing upward

Thank you for your time, Any questions?