32 - Friday, May 27, 1994 - North

AUTOMOTION
THE INSURANCE Institute
for Highway Safety reports
that the performance of
vehicle airbags differs
depending on design. For

- example, some sirbags will.
inflate at lower vehicle

- impact speeds than others,

_ some ave larger when fully

in@ated, and some will,
inflate much more quickly.

Airbag deployment thresholds
vary from one airbag to another,
but most are designed to inflate in
frontai collisions equivalent to hit-
ting a solid barrier at 15-20 kni-h. °

Some European Airbags, such
as those used by Mercedes-Benz
and BMW, deploy at higher thresh-
olds, about 24 km-h. The reason *

" for the difference is that European
vehicle manufacturers make the

. assumption that vehicle occupants
wiil be wearing their seatbelts.

Shore News

Seatbelts provide ample protection
for occupants in collisions at
speeds up lo 24 kin-h into a solid
barrier,

For the same reason, European
airbags are generally smaller in
size when fully inflated, Airbags in
American automobiles are larger
because many U.S, drivers do aot
wear their seatbelts,

It should Se noted that a crush
into a solid barrier at 20 km-h is
equivalent to much higher crash
speeds in real life, For example, a
car going 50 kmn-h that rear-ends
another car may not set off the
airbag. Crash energy can be dissi-

ated by heavy braking just before
impact, by deformation of the front
and rear ends of both cars and by
the act of pushing the car along the
road after the impact. Deployment
of the airbag depends upon the
actual deceleration of the car as
measured by the sensors in the
front of the car.

And, of course, an airbag will
not inflate in a side or rear colli-
sion, or roll-over, no matter how
severe the crash.

The number and location of
crash sensors differs from car to
car. Most systems use between one
and four electromechanical sensors
in the vehicle’s front end. These.
are either “ball-in-tube” or “spring-
mass” types where the ball or mass
moves in proportion to the crash
severity and makes an electrical
contact which inflates the airbag.

Mercedes-Benz and BMW
already have systems which vary
the deployment threshold depend-
ing on whether occupants are wear-
ing their seatbelts. To prevent a
passenger-side airbag from inflat-
ing when there is no one in the pas-
senger seat, BMW’s new 7-series
sedans now have a sensor in the

New council formed

THE MINISTRY of Transport,

Douglas Young, and the Chairman .

of Canadian National Railways,

Brian Smith, have announced the .

formation of the Greater Vancouver
Gateway Council. ;

The Council’s main objective is
4]

the improvement of the commercial
‘viability of the Gateway, and raise
awareness of the Gateway’s impor-
lance to the economies of the Lower
Mainland, Canada and the world. It

comprises: C.P. Rail System, C.N.
Railways, The Freser Harbour
‘Commission, the Vancouver

passenger seat which detects if it is
occupied.

When the crash sensors detect a
severe frontal collision, an elec-
tronic signal is sent to an inflator, a
small tube which contains a chemi-
cal culled sodium azide. The sodi-
un azide burns instantly creating
enough nitrogen gas to fill an
airbag ina traction of a second,

The ainount of sodium azide in
the inflator determines the speed of
inflation of the bag, This varies
from car to car,

A test by the U.S. National
Highway and Traffic Adruinistra-
tion found that airbag inflation
speeds vary from 160 to 220 km-h.

As I reported in a previous col-
umn, there have been some reports
of airbags injuring occupants by
“slapping” them at high speeds
causing abrasions. Three factors
can affect the likelihood of airbag
abrasions: the speed of the airbag
inflation; how close the occupant is
to the airbag when it inflates; and
the folding pattern of the dormant
airbag, including whether the
airbag is tethered inside.

Different folding patterns are
used to pack nylon material inside
the steering wheel hub, and the pat-
tera can affect the speed at which it
inflates. In addition, some airbags
are tethezed on the inside to control
the shape and size of the bag when
it’s fully inflated. At full deploy-
ment, tethered airbags on the dri-
ver's side extend 25-33 cm towards
the driver, Untethered bags extend
38-50 cm. Tethered airbags make it

‘much less likely that occupants will

contact the bag prematurely.

{nternational Airport Authority, the - 9

Vancouver Port Corporation, the
B.C. Federation of Labour, the B.C.

Maritime Emp!oyers Association,
the B.C. Trucking Association, the <%
B.C, Wharf Operators’ Association, |

the Chamber of Shipping of B.C.,
Air Canada and Canadian Airlines
International.

A new semi-monthly feature now every other
Friday in the Auto Guide. We invite you to ask
your questions about car repair and maintenance
of North Shore auto professionals.

Send your questions to: Auto Advice,

North Shore News,

1139 Lonsdale Ave.,

North Vancouver B.C. V7M 2H4

The Next issue of Auto Advice will be
published Friday May 6th in the

Afier an airbag inflates, it
quickly deflates so that the driver
may be able to see where they're
going if the vehicle is still moving,
The bot gas in the airbag vents
through holes in the sides of the
bag, and there are cases of peeples
forearms being burned by the hot,
escaping gas.

This problem has been virtually
eliminated in modern vehicles by
moving the Jocation of the vent
holes, ;

Future airbag developments
include “smart” airbags that will
inflate at different speeds depend-
ing on the severity of the crash, on
whether the occupants are wearing
their seatbetts and how close the
occupants are sitting to the airbags.

LUSION SPECIALISTS

For now, it's nice to know there
are no “bad” airbags; they all do
the job, only some do it with a Little
more precision.

PL Tere

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