meo@vaxine.UUCP (Michael O'Shaughnessy) (02/11/86)
There has been a lot of discussion about airbags, seatbelts, and
"personal freedom" on the net lately - much of it misinformed. As a former
police officer, let me say that seat belts save many lives. We never saw a
fatality that had been wearing a belt; many of the corpses we scraped off the
roads and interiors of cars could have lived if they had buckled up. We never
saw an instance where being unbuckled would have helped.
AIRBAGS
To my knowledge, the only airbags currently in standard production are
those on the Mercedes-Benz series of cars. Anti-lock braking systems (ABS) and
airbags are standard on some models, and are available as options on almost all
other models. The airbag comes as part of a package called the SRS, or the
Supplemental Restraint System, and includes a knee bolster to prevent occupant
submarining. In 1984 the SRS also included a seat belt tensioner for the
passenger's side only; starting in 1985 belt tensioners for both driver and
front seat passenger were made standard equipment on all models.
A few facts, taken from the sales literature and owner's manual:
The SRS system, in conjunction with the three-point seat belt, provides
improved passenger protection. The airbag is meant to supplement the seat belt
and its tensioner - NOT provide the only source of protection. (Hence its
name!)
The SRS consists of three major components. The airbag, fitted on the
driver's side only, is located in the center of the steering wheel. The knee
bolster is on the lower edge of the instrument panel on the driver's side. It
is intended to prevent the driver's lower body from being forced down and
forward in a major frontal impact (this motion is also known as submarining).
The emergency tensioning retractors are attached to the inertia reels of the
three-point seat belts. They are designed to tighten the front belts to
minimize the driver's and passenger's forward movement.
The system goes through a 10 second automatic check each time the car is
started, as indicated by a warning lamp. If the lamp fails to operate or
flickers during the self-check, it indicates a fault in the system. Faults are
not supposed to cause false activations, but may prevent proper activation when
needed. The owner is instructed to take the car to a dealer "without delay"
to have the system checked.
The single impact sensor is located at the forward end of the transmission
tunnel. It is designed to activate only during serious front end collisions.
The impact must be greater than approx. 12 mph, and the angle of impact must
be within approx. 30 degrees of head-on.
When a crash is detected, three gas generators are activated. One fires
the airbag, which emerges from the center of the steering wheel and inflates in
a preset pattern, inserting a cushion between the driver's head and upper body
and the steering wheel. The nylon bag has a volume of 60 liters when fully
deployed. A controlled deflation through four apetures in the bag's underside
begins with the impact of the driver's body against the air bag. The bag is
deflated within one second.
The other two generators which are fired are the two emergency tensioning
retractors. They are concealed within the central pillars, and consist of a
piston within a cylinder and the gas generator. The piston is connected by a
cable to the seat belt retractor reel. When triggered, the generator produces
gas pressure and drives the piston up the cylinder. The cable connected to the
piston turns back the seat belt reel and tightens the belt loop. The system
will only tighten the belt - a person leaning forward when it deployed will not
be flung back in their seat, but held in position.
If the car's battery is destroyed or disconnected on impact, an "energy
accumulator" (large capacitor?) stores enough energy to fire the system. If
the battery voltage is low, a "D.C. converter / step-up transformer" will
ensure proper operating voltage.
To prevent stray electrical signals from accidently triggering the system,
all system wiring uses shielded cables.
The service life of the airbag is limited; an expiration date is posted on
a large sticker in the glove box, and dealer inspection and/or replacement is
required at that time. The current service life is ten years from date of
manufacture.
"The closest approximation of the noise made by the inflating air bag is
that of a paper bag being burst at fairly close range."
"In case of minor head-on collisions, roll-overs, side and rear-end
collisions, as well as any other accidents in which no considerable forces act
on the front end, the airbag and tensioners are not triggered. The passengers
will then be protected in the usual way be the fastened seat belts."
"After activation of the SRS, the gas generator will temporarily release a
small volume of smoke in the vehicle interior. Ths smoke, however, is neither
injurious to your health nor does it indicate a fire in the vehicle."
I have had my 1985 190E, equipped with ABS and SRS, for 14 months and
19,000 miles now. On several occasions the ABS has prevented a serious
accident; I have fortunately not had a chance to test the SRS, but am grateful
that it is there if I need it.
Mike O'Shaughnessy, Automatix, Inc., 1000 Tech Park Drive, Billerica, MA 01821
Phone: (617) 667-7900 x2190
uucp: ...{encore,linus,spark,wanginst,wjh12}!vaxine!meo
P.S.: Allstate Insurance discount for airbags
Remember when Allstate's advertisements were telling us how wonderful
airbags were, and that any owner of an airbag equipped car would be eligible
for a 20% discount? I had to tell my agent about that provision; he knew
nothing about it. It turns out that the discount applies only to the medical
payment portion of the policy; that part dropped from $20/year to $16/year!
A whole $4!!! I wonder how much their ad campaign cost!! Needless to say, I
am looking for another insurance company.
P.P.S.: Ford's system
Ford will begin to offer its supplemental air bag system as a regular
production option on its Ford Tempo and Mercury Topaz models beginning in March
1986. Ford has been selling airbag equipped Tempo/Topaz cars to the federal
government and insurance companies since 1985. Some 2,000 bag-equipped units
were sold to private fleets in 1985 and 1,400 orders have been booked for 1986.
The driver's side only bag is a $815 option. It uses three sensors. I'll
post more details when I find them.