2_supplemental restraint systems_air bag

8/21/2019 2_supplemental Restraint Systems_air Bag

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RESTRAINT SYSTEMS

(SRS):AIR BAG SYSTEM


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1. Supplemental Inflatable

Restraint (SIR) System _Airbag

System Theory

Electrical System Components

Diagnosis

Servicing the Air Bag System

Objectives


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Learning Outcome

Identify and describe devices thatcontribute to automotive safety.

Describe the function and operation of air

bags.

Identify the major parts of a typical air bag

system.

Safely disarm and inspect an air bag

assembly.Know how to diagnose and service an air

bag system.


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OBJECTIVE

Supplemental Inflatable Restraint

(SIR) System

When a car crashes, the force required to

stop an object is very great because the car's

momentum has changed instantly while the

passengers' has not.

The goal of any supplemental restraint system

is to help stop the passenger while doing aslittle damage to him or her as possible.


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INTRODUCTION

The supplemental inflatable restraint (SIR)is a safety device used in conjunction with the

seat belt.

The air bag does not replace the function ofthe seatbelt.

The driver and the passengers must always

fasten their seat belts and adjust them for a

proper fit. The SIR is designed to protect the driver and

the front seat passenger in the event of a

significant frontal impact to the vehicle.


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_system

A passive restraint system operatesautomatically.

No action is required of the occupant to make it

functional


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The SIR System Components

The SIR System consists of a:-1. Driver airbag module2. Driver side airbag module3. Passenger airbag module

4. Passenger side airbag module5. Drivers and front passengers seat belt

pretensioners (and load limiter for somemodel)

6. Sensing and diagnostic module(SDM)7. Clock spring.8. Wire harness and connectors.9. AIRBAG indicator on the instrument cluster.

10. Side airbag


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SRS COMPONENT

1. Driver Airbag Module 4. Passenger Airbag Module

2. Clock Spring 5. Side Airbag Module

3. Sensing and Diagnostic Module (SDM) 6. Side Airbag Sensor


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SRS COMPONENT

1. Front impact sensor- To detect crash and sendthe signal to the air bag control module.

2. Airbag Control module- To receive the signalfrom the sensors and control the deployment ofairbag.

3.Airbag module- The air bag module is the air bagand inflator assembly

packaged into a single unit or module.

4. Wiring Harness- The electrical harnesses of theSIR system typically have yellow connectors toconnect the component in the system.

5.Clock spring contact- The clockspring allows forelectrical

contact to the air bag module at all times.


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SRS FUNCTIONS

Airbag Before Deployed

The bag itself is made of a thin, nylon fabric, which is

folded into the steering wheel or dashboardThe sensor is the device that tells the bag to inflate.

Inflation happens when there is a collision force equal

to running into a brick wall at 10 to 15 miles per hour (16

to 24 km per hour).A mechanical switch is flipped when there is a mass

shift that closes an electrical contact, telling the sensors

that a crash has occurred.


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SRS FUNCTIONS

The airbag's inflation system reacts sodium azide(NaN3) with potassium nitrate (KNO3) to

produce nitrogen gas.

Hot blasts of the nitrogen inflate the airbag.

Airbag being deployed


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SRS TRIGGERING DEVICE

The inflation system is not unlike a solid rocket booster.

The airbag system ignites a solid propellant, which burns extremely

rapidly to create a large volume of gas to inflate the bag.

The bag then literally bursts from its storage site at up to 200 mph(322 kph) -- faster than the blink of an eye!

A second later, the gas quickly dissipates through tiny holes in the

bag, thus deflating the bag so you can move.

Triggering device


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Powdery substance

The powdery substance released from the airbag,by the way, is regular cornstarch or talcum

powder, which is used by the airbag

manufacturers to keep the bags pliable and

lubricated while they're in storage.


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SRS OPERATION

This system makes the following judgments:unoccupied judgment, child seat judgment, childjudgment, and adult judgment.

In addition, it performs an initial check to checkthe circuit of the AIRBAG ON/OFF indicator lightswhen the ignition switch is ON.

The Occupant Classification ECU constantly

monitors the weight on the front passenger seat,and makes a judgment in accordance with thesignals from the occupant classification sensorand the state of the seat belt buckle switch,regardless of the position of the ignition switch.


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SRS OPERATION

The Occupant Classification ECU contains criteriavalue A to judge whether the seat is being

occupied by a child or a child seat in accordance

with the signals from the four occupant

classification sensors and seat belt buckle switch,and criteria value B to judge whether the

occupant is an adult or child (with child seat).

The Occupant Classification ECU makes an

occupied or unoccupied judgment in accordance

with the signals from the seat belt buckle switch.


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Unoccupied Judgment

(Occupant Classification ECU )

The Occupant Classification ECU makes anunoccupied judgment when the judgment value islower than criteria. To determine the occupancy of thefront and side passenger air bags, the weight of theoccupant is measured. If there is no occupant, the air

bags will not deploy during a collision.

If the ignition switch is turned ON in this state, thesystem performs an initial check, and does not

illuminate the AIRBAG ON/OFF indicator lights. Then,the system prohibits the deployment of the frontpassenger airbag, front passenger side airbag, andthe front passenger seat belt pretension, and does notblink the seat belt reminder light.


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Initial Check

After the ignition switch is tuned ON, the Occupant Classification ECU lights up

the AIRBAG ON/OFF indicator lights via Airbag Sensor Assembly based on the

timing chart below in order to check the indicator light circuits.


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SRS PROBLEMS

The supplemental inflatable restraints (SIR)

system includes a self-diagnostic function. If there

is a failure of the sensing and diagnostic module

or the external circuits, the SIR warning lamp inthe instrument cluster turns ON.

As a system check, the SIR warning lamp also

turns ON when the ignition is first switched to the

ON position.


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Correct Functioning

The system is working properly if:

The SIR warning lamp turns OFF after

approximately four seconds.


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Faulty Functioning

The system is not working properly, meaning one

of the SIR components or the wiring connector is

faulty, if:

The SIR warning lamp fails to turn ON when the

ignition is first switched ON.

The SIR warning lamp remains ON.

2_supplemental restraint systems_air bag

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