Porsche Airbag Systems

Also from Issue 179

  • Porsche at the Monterey Historics
  • Keep the Faith: Cool Beige 356 Outlaw
  • Interview: Brian Redman
  • First Drive: 2010 911 Turbo
  • Dig Deep: One-Owner 356 Speedster
  • 1,953-pound 911 SC
  • GT3 Cup-powered 1976 911
  • Market Update: 928
  • Icon: 908/02
  • 2010 911 Sport Classic
  • Project 914 3.6: Paint!
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Porsche Airbag Systems 1
Porsche Airbag Systems 2
The 1987 U.S. 944 Turbo was the first Porsche and the first vehicle to feature dual airbags as standard equipment.
Porsche Airbag Systems 3
A 964-based 911 undergoes crash testing.
By 1990, Porsche made dual airbags standard equipment in all models. Top to bottom: 944, 964-based 911, and 928.

The canister approach offers distinct advantages. First, its gas is released cold, so there are no hot spots. Because the gas is stored under high pressure, the 140-liter passenger-side airbag de­ploys faster, at about 30 milliseconds — similar to a driver-side airbag and about twice as fast as previous versions. When the unit receives an ignition signal, an internal steel cap is blown off, allowing pressurized gas to fill the airbag through holes and duct plates in the canister.

Porsche’s technical documentation for 1997 shows the factory had intended to include a passenger-seat occupancy sensor pad integrated into the seat surface material. If the seat was not occupied, the passenger-side air­bag would not deploy. However, we’ve never seen a 1997–2004 Boxster equipped with a passenger occupancy sensor. Interest­ingly, Porsche PST-2 and PIWIS diagnostic/pro­gramming equipment have areas for coding this sensor even though it appears that Por­sche did not install it.

The Boxster also got a new airbag control unit like the 993’s, with its internal MEMS accelerometer crash detection. The control unit will store up to ten faults, with a start-and-stop log kept for each fault. Data can be accessed and downloaded with the PST-2 or PIWIS testers. As in the 993, the Boxster control unit does not need to be replaced until the airbag has been triggered three times or if its fault memory cannot be deleted.

In 1998, Porsche introduced the 996 to the U.S. as a 1999 model with all air­bag up­grades seen in the 1997 Boxster plus more new technology that would be added to the Boxster. First and most important was the Porsche Side Impact Protection system (POSIP). The system deploys a 30-liter flat-cushion airbag between the occupant and door panel and side window to better protect the head and chest cavity (generally referred to as the thorax). The extra-large airbag was effective in any fore/aft seat position.

The new side airbags utilized argon/ helium-filled canisters pressurized to approximately 270 bar (3,969 psi). Side-impact sensors located in the doorsills triggered deployment depending on the angle of impact and measured acceleration. Unlike other airbags, these do not deflate after deployment. The door and door panel were redesigned to better help protect the pelvis, while a new control unit was used and referred to as the Multiple Restraint Systems unit, as it controlled front and side air­bags. MRS also has a crash output, which signals the central-locking system to unlock the doors while shutting off the fuel supply.

Porsche, never content with what is, added seatbelt tensioners and belt-force limiters in all 2002 models. The new seat­belt design used a pyrotechnic belt tensioner working in conjunction with the airbag system. When activation takes place, the three-point seatbelt tightens against the occupant’s chest, pulling the occupant firmly into the seatback so that less forward body movement takes place during abrupt deceleration.

Operation is achieved when the seatbelt tensioner receives a firing signal that ignites a pyrotechnic charge. The explosion creates gas pressure that pushes a piston that moves a line of ball bearings past a pinion at the reel, which winds the belt back in. The event takes place in approximately 20 milliseconds. The system also incorporates a belt-force limiter to stop the belt from tensioning beyond a specific point.

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