Chery A15. Manual - part 156

  Chery A15 Maintenance Manual 

 

Section Two: Working Principle of Airbag System 

 

I. Working Principle of SRS 

When the vehicle collides with other objects, the collision between vehicle and the 

other object is called primary collision, after which vehicle speed will be rapidly 

decreased, while the driver and passengers will move forward due to inertia force and 

collide with steering wheel, windshield or dashboard and other inside components, 

this is called secondary collision. Secondary collision is the major cause of the 

driver’s injuries in vehicle accidents. To relieve or avoid driver’s injuries in secondary 

collision, some passive protection units such as safety belts and airbag are equipped in 

vehicles. 

The purpose of airbag design is to quickly form an air cushion between driver and 

inside components during the short period of time (50ms) between primary and 

secondary collisions, as shown in the figure, to support driver’s head and chest with 

an air cushion and absorb the kinetic energy produced by body inertia with damping 

action of the airbag, so as to protect driver’s body. 

 

Activated airbag system

 

 

 

 

 

 

 

Airbag system is a safety unit to be used together with safety belt. 

Airbag dose not replace safety belt in its function. 

Driver must always wear safety belts with proper tightness. 

 

  Chery A15 Maintenance Manual 

II. Working Conditions 

Airbag system is activated under any one of the following circumstances: 

1). When a vehicle running at 25Km/H collides with a still object; 

2). When two vehicles running at 25Km/H in opposite direction collides with each 

other (airbags activated in both vehicles);   

3) When a vehicle running at 50Km/H collides with a still vehicle on the front 

(airbags activated in both vehicles); 

4). Collision within the range of 30º angle on both sides. 

 

 

 

 

 

 

 

 

 

SRS is designed to provide protection for driver against injuries caused by heavy 

frontal collision of vehicle. Any external force coming in an angle within 30º from 

vehicle centerline shall activate airbag. 

Important: Above mentioned vehicle speeds all refer to sensor-monitored speed, not 

actual vehicle speed. Sensor-monitored speed is related to actual speed, bumper effect, 

frame deformation, etc. 

 

 

 

 

 

 

  Chery A15 Maintenance Manual 

III. Working Procedure 

Activation procedure of airbag 

 

Accident occurring 

Sensor working 

System activated 

Airbag triggered and inflated 

 

 

Airbag fully inflated 

Driver moving forward 

 

 

   

 

Head and chest sunk in airbag 

Air coming out from rear side of airbag 

 

 

 

Airbag emptied 

 

 

 

Working process: 

Electronic accelerometer continuously measures vehicle acceleration and deceleration, 

then transmits signal to microprocessor. 

Microprocessor determines, by sophisticated collision signal processing, whether to 

trigger airbag and when to trigger. 

  Chery A15 Maintenance Manual 

In case airbag is to be triggered, microprocessor activates ignition circuit. 

If electric safety sensor is off at the same time, ignition current convects through 

trigger to inflate airbag. 

 

 

Obstacle prevails over “signal”

 

 

Accident sensor

 

 

Damage is greatly delayed

 

 

 

 

 

 

Coordinate Diagram of Airbag Activation Procedure 

 

IV. Airbag Component Parts and Working Principles 

SRS (airbag system) includes: 

Steering wheel airbag subassembly; 

Airbag control module; 

Steering post hairspring; 

Wire harness; 

SRS fault warning light. 

1. Collision Sensor (inside BCM) 

Collision sensor or accelerometer indicates vehicle acceleration or deceleration in 

frontal collision with electronic instruments, in which the electronic signals 

proportionally reflect vehicle acceleration or deceleration (acceleration of gravity). 

Computer decides the collision severity according to the strength of electronic signal. 

If electronic signal strength exceeds set value, airbag computer will immediately send 

command ignition signal to ignitor to generate air for inflation by heating inflating 

agent. 

2. Safety Sensor (inside BCM) 

Most vehicles have a spider-structured connector between airbag computer and ignitor