How do Airbags get tested? - VTI SL Comunicación

23/02/2021 12:05h Aeronautical, Automotive, Railway, Singular Projects

How do Airbags get tested?

The airbag is one of the most popular passive safety elements. The airbag function is to prevent people hitting the rigid parts of the vehicle directly. When a part of the body collides with the airbag, kinetic energy is absorbed, dampening the impact and reducing the severity of possible damage.

Originally, the airbag was located in the steering wheel minimizing driver’s head and body truck impact with itself. Currently, additionally to the front airbag, there are side, rear, curtain airbags models... located in seats, doors, dashboards ... minimizing damage to the rest of vehicle occupants and including other parts of body like legs, especially knees.

In fact, airbags have expanded their range of action from the vehicle interior to exterior, fit some car models with airbags on the hood and bumpers for the protection of pedestrians and even in vests and other clothing for motorcyclists and cyclists.

 But… how does an airbag work? 
An airbag consists of a bag module and a control unit with its corresponding sensors. The bag, mostly made of nylon, with adequate dimensions and venting, contains one or more gas generators and ignitors.
The ignitor transforms the electrical signal into heat, triggering a small detonation inside gas generator producing the gas necessary for bag inflated.

Once the impact takes place, the vent valves will regulate the pressure in the bag avoiding a sudden deceleration throughout the operating range.
How are they tested?
To make sure that the airbag works as expected, there are many tests that it must undergo. Without trying to cover all the tests, in a first classification, and if we limit ourselves to the conformity of production tests (CoP), we can distinguish:

  • At a first level the tests on bag module components. Bag and its folding, ignitor and gas generator are tested independently by their manufacturer. As in any CoP test, only a representative sample are tested. Especially in the case of ignitors and gas generators, their correct activation in the presence of the established signal is as important as the lack of response when it is not produced.
  • At a second level, the airbag bag manufacturers test the bag with all its integrated components verifying that the deployment occurs according to the expected parameters. Volume and time deployment are generally measured.
  • At a third level, the bag already integrated in the corresponding car component is tested.On this occasion, the aim is to verify the correct deployment of the bag in real conditions where the folding and the force necessary to break the component play a fundamental role.
  • We could reach a fourth level, already within the homologation tests, in which the airbag integrated in the component is tested together with the launch of the corresponding anthropomorphic form, allowing the impact analysis.
  • Control units usually have their own laboratory tests, which we will not delve into, in order to ultimately carry out tests of the complete vehicle on track and full crash.

Vehicle Component Integrated Airbag Deployment Tests
The component-integrated airbag deployment tests are ruled by general international regulations (in Europe, the Crash Standard - UNECE, and in the USA, the FMVVS-208) and the requirements of the component and complete vehicle manufacturer.

The tests take place in conditioned rooms within the different laboratories where the Airbag Deployment System (ADS) generates an electrical signal that simulates the control unit deployment trigger.

The signal consists of a set of individualized electrical pulses with configurable amplitude and period. Although the values are highly dependent on the model, in general, these are square pulses of approximately 1,75A and 2ms.

The ADS is as in charge of the generation of the trigger pulse as of the acquisition at high frequency of voltage and intensity measured in the ignitor squib terminals.

To verify start and end conditions of the airbag under test, the ADS measures the resistance at ignitor squib terminals before and after the test, aborting the test if the conditions are not appropriate.

Regarding the room conditioning, we must not forget that the ignition of an airbag is a small detonation in which small particles are also generated, which although they are not harmful if inhaled occasionally (as expected in an accident), can cause health problems under continuous contact such as that which could occur in the testing laboratory.For this reason, it is essential that the rooms have appropriate acoustic insulation, extraction system and access control.

Different regulations usually require that tests -in addition to room temperature- be carried out at high and low temperatures (the ranges depend on the manufacturer, but 80ºC, 20ºC and -10ºC can be taken as reference values).Therefore, it is necessary for the room to be air-conditioned and to have a specific element for air-conditioning the airbags, such as climatic chambers.

Finally, we must consider that to verify both temporally and dimensionally the deployment of the bag, it is necessary to film the sequence at high speed. The deployment of an airbag occurs in less than 30ms.Therefore, the deployment room must have an appropriate recording and lighting system.

Our ADS is a highly customizable modular and versatile system that allows from, in its simplest version, the performance of individual CoP tests of the igniter, gas generator or bag as a whole, to the tests described here with room management, reaching more complex development tests with the possibility of acquisition and signal treatment of other specific parameters, analysis and presentation of results on demand.

Checking an airbag may seem like a comprehensive set of tests but every single detail is important to be safer behind the wheel

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