Note: Descriptions are shown in the official language in which they were submitted.
1247-29 ~3~
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PASSENGER COMPARTMENT SENSOR WITH LOW BIAS
Background of the Invention
It has been found that in a 30 mph frontal barrier
crash a restraining device such as an air bag must begin
restraining the dr1ver by the time the driver has moved
forward about 5 inches if it is to prevent injury. Air bag
inflating mechanisms require a period of time, such as 30
milliseconds, to effect inflation of the air bag once a
signal initiating inflation has been received from a s~nsor.
It has also been determined that a passenger protective
~device is needed in accidents in which movement of the
vehicle occupant relative to the vehicle reaches a velocity
of about 12 ~ph or greater. Thus, a sensor is required
which will determine that ~he occupant will collide with
~; some portion o the vehicle's interior at a speed of 12 mph
or greater and ~or a 30 mph frontal barrier or equivalent
crash initiates air bag inflation a pleriod of time such as
30 milliseconds before the occupant has moved forwarded 5
inches.
It lS important that the sensor which initiates
operation of the air bag inflation means be responsive to
the acceleratlon of the passengçr compartment rather than
some other part o~ the vehicle because this location leads
to certain advantages compared with other sensor locations.
For example, if a ront fender or bumper o the vehicle
should collide with a pole or the like which breaks upon or
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shortly after impact, a sensor mounted on the front fender
or bumper could experience a ~elocity change of 12 mph or
greater before the pole breaks, whereas the passenger
compartment of the vehicle might experience a negllgible
velocity change. Under these circumstances, inflation of
the air bag is not required and if inflation occurs, it
might even contribute to a subsequent accident. It is
important, therefore, that the sensor or sensors with which
a vehicle is equipped be located in such positions and be of
such construction as to be predictive that the passenger
compartment will undergo a velocity change necessitatiny
passenger protection.
The mechanical crash sensor designs (as distinct from
electronic) that have been made in the largest quantities
are the spring mass sensors. The term "spring mass" or
"undamped spring means" as used herein means those sensors
wherein the motion of the sensing mass is controlled only by
the acceleration experienced by the sensor, its
translational or rotational inertia and a bias force such as
would result from a spring, a magnet or a rolamite-type
band. The spring mass sensor is known to function adequately
for short duration crash pulses. Such pulses are
characteristic of head on crashes or standard barrier
impacts. When the vehicle on which the sensor i5 mounted
e~periences a deceleration pulse greater than -the biasing
force on the sensing mass, such as would accompany a crash,
the sensing mass moves rapidly towards the forward end of
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the vehicle, and initiates air bag inflation.
As a point of reference, the maximum acceleration due
to application of the vehicle brakes may be considered to be
about 0.7g.
Previously proposed systems have included crash sensors
mounted outside the crush zone. Heretofore, all such
sensors, have had biases above about 7 g. All of these
prior art sensors have been, in fact, level detectors rather
than velocity change detectors. In the case of a crash in
which a vehicle travelliny 3Q mph impacts an object causing
a constant acceleration of slightly less than than 7 g's,
such as might be approximated when a vehicle impacts one of
the crash cushioning devices now placed around many rigid
roadside structures, the occupant would sustain serious or
fatal injuries. This is certainly an accldent requiring an
air bag and yet no prior àrt mechanical sensor would have
fired. mass~ Other situations where prior art mechanical
sensors can fail are impacts with snow banks, striking
flooded areas of roadways or impac~ing soft earth.
Furthermore, certain of the prior art sensors when
loca~ted wlthin the passenger compartment fail to distinguish
between an actual crash condition requiring an air bag and
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conditions not requiring an air bag such as car bottoming,
travel over a curb, railroad track or pot hole. Prior art
sensors located in the passenger compartment which have high
g biases are very sensitive to extremely short pulses
normally encountered in such conditions and would cause the
air bag to inflate unnecessarily.
Summary of the Invention
A principal object of the present invention is to
provide a passenger compartment mounted sensor that will
alleviate the problems inherent in and encountered by the
earlier proposed and prior art sensors when located outside
of the crush zone and, specifically, in the passenger
compartment.
Another object is to provide a passenger compartment
mounted sensor which possesses a low bias and is responsive
to velocity change which requires the acceleration to be
sustained above the bias level for an extended period of
time.
Brief Description of the Drawings
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~: ~ : Fig. 1 is a schematic view of a passenger compartment
of a vehicle showing air bag systems incorporating sensors
: of:the invention;
Fig. 2 is an exploded perspective view of the air bag
;:: system with certain parts broken away and removed;
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Fig. 3 is a side elevational view of the sensor with
the gas generator with certain parts broken away removed and
with a pin extending from a steering wheel nut employed for
enabling the sensor when wheel mounted;
Fig. 4 is an enlarged fragmentary view including the
end of the D-shaft and the mounting plate supporting the
D-shaft;
Fig. 5 is a top plan view of the sensor with the cover
removed and other parts broken away and removecl showing the
sensor armed and with dash lines showing the sensor when it
is safe;
Fig. 6 is an enlarged fragmentary view of the sensor
showing the mass and associated pin extending from the
D-shaft prior to movement of the mass incident to a crash;
Fig. 7 is a similar view showing the mass shifted as a
result of a crash and the movement of the associated pin and
the D-shaft;
Fig. 8 is an enlarged fragmentary view of the firing
;~ ~pin held in a retracted position by the D-shaft.
Fig. 9 is a similar view with the firing pin released
à~ter a collision is experienced.
Fig. 10 lS a view similar to Fig 6 showing an alternate
embodiment of this invention which is an undamped spring
;; mass sensor.
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DETAILED DESCRIPTION
In the drawings, air bag safety restraint systems 8 and 8'
- incorporating the sensor of the invention are shown mounted
within the passenger compartment of a vehicle both at the
driver side and the passenger side. This sensor - initiator
l0 is preferably mounted lnside of the gas generator or
inflator 12. However, the .sensor - initiator may be
otherwise mounted but nevertheless located in the passenger
compartment. The inflator 12 is symmetrically mounted on a
frame 14 to which is also mounted the housing or cover 16
for the folded air bag 18. Interposed between the inflator
and the air bag is a diffuser plate 20 also secured to the
frame 14.
The air bag safety restraint system 8 of the present
nvention is mounted on the vehicle steering wheel 22
through the frame 14. The steering wheel 22 includes an
outer rim 24, and a suitable number of radial spokes 28.
~; ~The air bag safety restraint system 8' is suitably mounted
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on the passenger side of the compartment and may contain two
gas~generators and sensor assemblies which may have the same
or diferent crash sensitivities.
The gas;generator 12 includes housing 32 containing a
gas generating material 34 which may be sodium azide.
Sodium azide is stable over a wide temperature range~ but
when iynited, rapidly decomposes releasing a large volume of
nitrogen gas.
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Reference is now made to the sensor-initiator 10 shown
in detail in Figs. 4-9. In order to increase reliability, a
pair of redundant damped sensors 38 are adapted to actuate
respective primers 36 within the housing 40. Each sensor 38
includes a damped sensing mass 41 capable of limited
movement within the cylinder 39 in the block 44 contained
within the housing 40. Before the air bag safety restraint
system 8 is mounted on the steering wheel 22 movement of the
sensing mass 41 within the respective cylinder 39 is
prevented by means hereinafter described. When the system
is mounted on the steering wheel, an extension 48 which is
part of the nut 50 which holds the steering wheel on~o the
steering colun-m enters the lock pin hole 51, in the
sensor-initiator 10. This pin extension 48 shifts the
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conical lock pin 54, permitting the sensing mass lock arms
52 to rotate out of the path of the sensing masses 41,
thereby arming the system. The locking arms 52 have a
common connection and operate under the bias of springs 55
which urge the arms towards one another. The arms are kept
apart and`consequently in engagement with the sensing masses
41 to prevent movement of the sensing masses 41, as a result
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of the conical shapé of lock pin 54. When the sensors are
rendered safe, the larger diameter part of the conical pin
54 is engaged with the arms 52 to thereby keep them apart
and consequently in engagement with the sensing masses 41.
When the pin 54 is moved inwardly the smaller diameter of
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the conical shape of the lock pin 54 is exposed to the arms
which when under the influence of the springs 55 are moved
towards one another to thereby free the sensing masses 41.
As explained previsusly, the inward movement of the conical
pin 54 is caused by the pin 48 of the steering wheel nut 50.
Each sensing mass 41 is associated with a pin 56
extending from a "D-shaft" 58. The other end of each pin 56
includes the spherical ball 60 in engagement with a biasing
spring 62 to assure the interengagement of pin 56 with .its
associated sensing mass 41. Each D-shaft 58 is provided
with a face 64 formed in a generally cylindrically shaped
extericr surface. In addition a spring biased firing pin 66
is in alignment with the primer 36 and i.s maintained in a
retracted position by the cylindrically shaped portion of
the D-shaft 58 and is permitted to be released when aligned
with the face 64.
In the event that an automobile experiences a crash,
each sensing mass 41 moves to the right as shown in Figure
7. However, ~his motion is resisted by the bias spring 62
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acting through the pin 56 and by the air pressure
differential between the left and right sides of the sensing
mass 41. This pressure is gradually relieved by virtue of
the air flowing in the clearance between the sensing mass 41
and cylinder 3~. If the crash is of sufficient severity,
the mass 41 will move sufficiently to the right to cause the
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D~shaft 58 to rotate enough to clear the firing pin 66 and
permit it to move past face 64 and impact against primer 36
which then ignites to initiate the ignition of leads 68
which cooperate in initiating the burning of the gas
generate material 34, which, in turn, inflates the air bag.
In Fig. 10, an example of a pure spring mass sensor 38'
is shown having an essentially undamped sensing mass 41'.
In all other respects this sensor-initiator 10' is the same
as sensor initiator 10 of Figs. 4-9 and like numerals will
be used with an accompanying prime for corresponding parts.
With respect to all sensors incorporating the teachings
of this invention, and particularly the spring mass sensors
whether damped or undamped, relatively low biases,
preferably around 4 g and less than 7 g are contemplated,
because of the location within the passenger compartment. In
addition the sensors of this invention are velocity change
detectors in the sense that they require a substantial
velocity change to take place after the blas acceleration
has been exceeded which requires that the acceleration be
sustained above the bias for a substantial period of time.
Normally this time will range from 15 to 100 milliseconds
depending on the magnitude of the acceleration. In this
manner, unnecessary air bag deployment will be minimized,
and the air bag will be deployed when needed in cases
involving long low acceleration crash pulses such as result
from impacts with crash cushions.
When two sensor initiators are used for a passenger
side system the sensitivity of the sensors could be
different or alternately a pyrotechnic delay could be used
with one of the sensor initiators to cause a staging of the
air bag inflator. Such staging would be useful to reduce
injury to out of position occupants.
Acceleration as used herein means acceleration of the
vehicle in the reverse direction as would occur in a crash
wh~re the velocity of the vehicle is reduced or when a
stationary vehicle is struck in the ~ront causing it to
accelerate backwards.
Primers as used herein includes any pyrotechnic device
such as stab primers, stab detonators or electric squibs.
Thus the several aforenoted objects and advantages are
most effectively attained. Although several somewhat
preferred embodiments have been disclosed and described in
detail herein, it should be understood that this invention
is in no sense limited thereby and its scope is to be
determined by that of the appended claims.
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