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Shorting Bar ESD Sacrificial Spark Gap Disclosure Number: IPCOM000147695D
Publication Date: 2007-Mar-21
Document File: 3 page(s) / 776K

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The Prior Art Database


ESD Sacrificial spark gap by means of ignitor shorting bar 81154960

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                                                5th January 2007

Subject:  Defensive Publication – ESD Sacrifical Spark gap.


It is possible for electrostatic charges to be generated in automotive vehicle, e.g. by passengers moving in their seats, cleaning trim, vehicle driving over different road surfaces, vehicles covers being removed , etc.  In rare cases these static charges can reach a high level and be transferred to the interior trim and then migrate to the Restraints protection devices, e.g. driver, passenger, side, knee airbags, seat belt pretensioners.  If appropriate countermeasures are not designed for electrostatic discharge, ESD, there is the possibility that this charge can pass to the pyrotechnic device and travel to the vehicle ground through the device wiring, possibly resulting in rare cases in deployment of the device.

Known countermeasures include

  1. Fixing the device to the body so any charge goes directly to ground rather than jumping from say the inflator body to the ignitor pins
  2. Adding a ground wire between the device and vehicle ground, (which can also act as an antenna for picking up stray RF energy)
  3. Increasing the strength of the ignitor to reduce its susceptibility to ESD, (may require higher current to deploy increasing cost of deployment electronics)
  4. Adding a varistor or capacitor in parallel with the ignitor bridge, either directly across the bridgewire, or in the connector socket
  5. Using a sacrificial spark gap between one of the ignitor pins and the metal inflator housing.  This has been used successfully on early European inflators, however is difficult to adopt now as ignitor specifications require environmental testing at a component rather that inflator assembly

Typical inflator housing & standard ignitor         Davey Bickford Ignitor with sacrificial spark gap

                                                                                                                                    Ignitor pin to housing


Spark gap housing to pins ~ 3 to 6 kV                                            Housing to bent pin ~0.5 to 1 kV

~ 1.5mm air gap    ...