Angled vehicle crash sensor

The sensor means crashes earlier and discriminates better when mounted at an angle to a horizontal plane passing through the horizontal axis of the vehicle. The sensor preferably is of the damped ball-in-tube type and the angular mounting thereof ranges from 10 to 40 degrees with respect to the horizontal axis of the vehicle, with the forward end of the sensor lower than the rear.

BACKGROUND OF THE INVENTION 
This invention relates generally to crash sensors for use in vehicles 
equipped with airbags. More specifically, the invention relates to the 
placing of the crash sensors. 
The present invention also constitutes an improvement over co-assigned U.S. 
Pat. Nos. 4,284,863, 4,329,549, 4,573,706 and 4,580,810, the disclosure 
thereof being incorporated therein by reference in accordance with 
accepted legal principles. 
U.S. Pat. Nos. 4,284,863 and 4,329,549 are damped ball-in-tube crash sensor 
designs. 
In U.S. Pat. No. 4,573,706, there is disclosed and claimed a mechanical 
sensor with a low bias for mounting within a vehicle passenger compartment 
which is operable without electric power for igniting the pyrotechnic 
elements of an airbag safety restraint system where the sensor comprises a 
sensor train which includes a sensing mass, a spring bias, a firing pin 
and a primer; and means responsive to sustained acceleration primer and 
initiate airbag inflation. 
U.S. Pat. No. 4,580,810 discloses and claims an airbag system adapted to be 
mounted on the axis of a steering wheel of a vehicle wherein the sensor is 
mounted inside an inflator for the airbag. This system includes an 
inflatable airbag; a gas generator having a housing and ignitable 
gas-generating material contained therein in fluid communication with the 
interior of the bag which is external to the housing. The system also 
includes ignition means for igniting the gas-generating material which is 
within the housing and a sensor also mounted within the housing of the gas 
generator for sensing the crash and initiating the ignition means. 
It is known that when mounting a sensor on the steering column of a 
vehicle, the sensor normally rotates with the steering column and thus in 
order for the sensor to have the same orientation regardless of the angle 
of the steering column, the sensor axis must be parallel to the axis of 
the steering column. The inventor's research has shown that the steering 
column mounted sensors frequently fired earlier than other passenger 
compartment mounted sensors having the same calibration. This would found 
to be caused in some cases by the coupling of the steering column with the 
crush zone of the vehicle. In other cases, the steering column was not 
coupled with the crush zone but still the sensor fired early; the crush 
zone being that portion of the vehicle which experiences a velocity change 
early in the crash before the entire vehicle has slowed down. The 
inventor's study concluded that placing a crash sensor at an angle to the 
horizontal makes it additionally more sensitive due to the vertical 
accelaration components present in a vehicle crash. 
INFORMATION DISCLOSURE STATEMENT 
Prior publications as exemplified by U.S. Pat. Nos. 2,649,311; 3,563,024; 
3,859,650; 4,116,132; 4,167,276; 4,172,603; 4,161,228; and 4,204,703 are 
generally illustrative of various systems of this type. 
Very pertinent to this invention are the co-assigned patents mentioned 
above. 
In the general appreciation of the prior-described device, it can be said 
that these are often acceptable for their intended purposes, but they are 
not entirely satisfactory for a number of reasons, in particular because 
of their failure to fire as rapidly as would be desired and their ability 
to distinguish between airbag-desired and airbag-not-desired crashes. 
There is continuing research in ways and means to accelerate such firing 
and improve the crash discrimination ability of the sensors. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an angled passenger 
compartment sensor which fires earlier than prior art passenger 
compartment-mounted sensors, owing to the angular mounting thereof 
relative to the of the vehicle equipped therewith. 
A second object of the present invention is to provide an angled crush zone 
sensor which fires earlier than prior art crush zone mounted sensors 
owning to the angular mounting thereof relative to the of the vehicle 
equipped therewith. 
Another object is to provide a sensor which possesses a low bias and is 
responsive to velocity changes which require the acceleration to be 
sustained for an extended period. 
Another object of the invention is to provide a mechanical or electronic 
sensor that is responsive to a portion of the vertical acceleration 
components of a vehicle crash. 
Another object of this invention is to provide a system of this character 
which combines simplicity, strength and durability in a high degree 
together with inexpensiveness of construction and facile mounting. 
Other objects of this invention will in part be obvious and in part 
hereinafter pointed out. 
This invention resides in the concept of mounting a sensor at an angle to a 
horizontal plane passing through the vehicle for which it is designed. 
Preferably, the angle of mounting of the sensor ranges from 10 to 40 
degrees with respect to the horizontal. A preferred range for the optimum 
angle of mounting is between 20 and 30 degrees. The exact angle will vary 
from car to car and for different mounting locations and must be 
determined on a case by case basis.

DETAILED DESCRIPTION 
In the drawings FIG. 1 shows a sensor (10) mounted within a housing (11). 
The housing is defined with one wall thereof constituting bracket 13. As 
shown the sensor is incline at 30 degrees from a horizontal plane of the 
vehicle. The bracket (13) is adapted to be installed on a vehicle. 
In the embodiment shown in FIG. 2, an airbag safety restraint system (8) 
incorporating a sensor (10) is mounted inside the gas generator inflator 
(12). The inflator (12) is symmetrically mounted on a frame (14) to which 
is also mounted the housing or cover (16) for the folded airbag (18). The 
airbag housing or cover (16)is made of a frangible plastic material and 
encloses and protects the folded airbag (18) to prevent damage to the bag 
when it is stored and in its uninflated condition. 
The airbag safety restraint system (8) can be mounted through its frame 
(14) anywhere in the passenger compartment but at an angle between 10 and 
40 degrees to the horizontal axis of the vehicle. This is done by either 
inclining the housing (16) downward within that angular range or by 
placing sensor (10) which then is secured by its frame (14) parallel to 
the horizontal axes of the vehicle. 
As is customary, the gas generator (12) includes a housing (32) containing 
a gas generating material which suitably is sodium azide which is suitable 
over a wide range of temperatures but which when ignited, decomposes, 
rapidly releasing a large volume of nitrogen gas. 
Reference is now made to the sensor initiator (10) shown in detail in FIG. 
3. 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) contains a damped sensing mass (41) capable of 
limited movement within the cylinder (39) in the block (44) contained 
within the housing (40). Before the airbag safety system is mounted in the 
passenger compartment, movement of the mass (41) within the respective 
cylinder (39) is prevented by means hereinafter described. An extension 
not shown which is part of a device mounted in the passenger compartment 
enters a lock pin hole in the sensor initiator (10). The pin extension 
shifts the conical lock pin permitting the sensing mass lock arms (52) to 
rotate out of the path of the sensing mass (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 of the conical pin 
(54) when it 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 the conical shape of the lock 
pin (54) is exposed to the arms which then under the influence of the 
springs (55) are moved towards one another to thereby free the sensing 
masses (41). The inward movement of the conical pin (54) is caused by an 
external arming pin which is attached to the vehicle where this airbag 
module is to be mounted. 
Each sensing mass (41) is associated with a pin (56) extending from a 
"D-shaft" (shown in FIG. 4 as 58'). The other end of the pin (56) includes 
the spherical ball (60) engagement with a spiral biasing spring (62) shown 
as spring 62' in FIG. 4 to assure the interengagement of pin (56) with its 
associated sensing mass (41) and to provide the proper bias against motion 
of the sensing mass. Each D-shaft (58) is provided with a suitable surface 
formed in a generally cylindrical shaped surface. In addition, a spring 
biased firing pin is placed in alignment with the primer (35) and is 
maintained in its retracted position by the cylindrically shaped portion 
of the D-shaft (58). It is permitted to be released when aligned with the 
face of the shaft. 
In FIG. 4, a pure spring mass sensor is shown having an essentially 
undamped sensing means (41') which normally will travel a longer distance 
than in the case of damped spring mass sensors. In all other respects, 
this sensor initiator is the same as sensor initiator (10) of FIG. 3 and 
like numerals were used with accompanying primes for the corresponding 
parts. 
It is also possible to use a damped spring mass sensor where the dampening 
is created by a sharp edge orifice in the piston such as is disclosed in 
U.S. Pat. No. 3,563,024. 
In FIG. 5 an electronic sensor is illustrated wherein the sensing mass 
(41") is shown placed on an angle in the sensor. This sensor is suitable 
for mounting on the tunnel of a vehicle in conjunction with the electronic 
diagnostic circuits. The motion of the sensing mass (41") causes the 
electrical strain gauges 100 to change in portion to the acceleration of 
the sensing mass. This resistance is part of an electronic circuit 101 
which responds to the resistance change to determine the severity of the 
accident and thus to initiate an airbag inflation when desirable. In 
another configuration the stain gauge system can be replaced by a Piezo 
electric crystal. In this case, the electronic circuit monitors the output 
from the Piezo electric crystal instead of the stran gauge resistance. The 
electronic sensor shown here differs from known electronic sensor 
primarily in the fact that the sensing mass is placed at an angle with 
respect to a horizontal plane of the vehicle. 
With respect to all the types of sensors incorporating the teachings of the 
invention, it is to be noted that their operation is improved by being 
mounted angularly and downwardly in the passenger compartment. 
Referring now to the graphs of FIGS. 6 through 10, it will be clear 
therefrom that the mounting of a crash sensor on a downward angle is 
desirable. 
A ball-in-tube crash sensor has one uncontrollable degree of freedom which 
is the location of the ball in the cylinder. If the ball goes down the 
center of the cylinder without touching a side, then it will take a 
considerably larger velocity change for the ball to travel a given 
distance than if the ball is resting against the side. This is due to the 
fact that the air flow restriction is proportional to 2.5 power of the 
clearance. If the clearance has a crescent shape such as would be the case 
when the ball is against the side of the cylinder, it can be demonstrated 
mathematically that the flow resistance is approximately half of the 
resistance when the clearance has a circular or ring shape. Moreover, if 
the ball is allowed to whirl around inside the tube, energy will be 
dissipated in the form of friction which will similarly downgrade the 
performance of the sensor particularly for marginal crashes. For car 
sensors, therefore, it is desirable to mount the sensors of an angle so 
that there is a predominant acceleration vector component holding the ball 
against one side of the cylinder. 
In distinguishing between certain types of crashes which are characterized 
by long pulses, it has been found that vigorous crashes such as high speed 
car-to-car A-pillar impacts have a substantial vertical acceleration 
component, whereas non-vigorous crashes such as 9 mph frontal barrier 
impacts, for example, do not have a significant vertical component. When 
sensors are mounted horizontally, they cannot distinguish between these 
two crashes. It was found, unpredictably and unexpectedly, that when they 
are mounted on an angle pointing downward, the resultant acceleration 
which is composed of both vertical and horizontal components renders the 
two crashes distinguishable. This is readily apparent from the curves of 
FIGS. 6 through 11. 
The two crashes which are plotted in FIGS. 6 through 11 are respectively 45 
mph car-to-car 30 degree A-Pillar impact where the car studied is a target 
car; and a 9 mph frontal barrier impact. By overlaying the plots of FIGS. 
6 and 7, it will be noted that the velocity curves are essentially 
indistinguishable after allowing for Five millisecond delay in the 
A-pillar impact. This indicates that it would be extremely difficult or 
impossible to design a crash sensor which would fire on the A-pillar 
impact and not fire on the 9 mph barrier impact. FIGS. 6 and 7 show the 
horizontal acceleration components of the two crashes where the 
accelerometers are located on the vehicle transmission tunnel. In each 
curve the acceleration has been integrated to give the velocity change of 
the tunnel relative to a coordinate system moving at the pre-crash 
velocity. The velocity curves are marked VEL. The firing times of a sensor 
designed for this location is shown in FIG. 10 at about 65 milliseconds 
for the A-Pillar impact. It did not fire on the 9 mph barrier impact of 
FIG. 11. 
FIGS. 8 and 9 show the vertical accelerations for the same two crashes at 
the same location. Whereas the horizontal accelerations and velocities 
were very similar for these two cases, the vertical accelerations and 
velocities are markedly different. Thus, if the sensor was rotated so that 
it was sensitive to a portion of the vertical acceleration components as 
well as most of the horizontal acceleration components a sensor could be 
designed which would distinguish between these two crashes. This is 
illustrated in FIGS. 10 and 11, where the acceleration resolved about an 
axis which has been rotated 24 degrees relative to a horizontal plane is 
shown. If these two plots are overlayed, one will note that the velocity 
curve for the 9 mph barrier impact is virtually unchanged, whereas the 
velocity curve for the A-Pillar impact shows a marked oscillation. In 
fact, the A-Pillar impact velocity curve is much steeper in the period 
from 50 to 75 milliseconds than is the velocity curve on the 9 mph impact. 
Research by the inventor has shown that the sensor should be pointed 
downward, rather than angularly upward to gain maximum improvement in 
firing response. Thus, the sensor fired in 65 milliseconds when rotated 
downward 24 degrees, but did not fire until 89 milliseconds when rotated 
upward by 30 degrees. This was totally unexpected to one skilled in the 
art. 
When mounting a sensor on the steering wheel of the vehicle as disclosed 
and claimed in U.S. Pat. No. 4,580,810, the sensor normally rotates with 
the steering wheel and thus in order for the sensor to have the same 
orientation regard be parallel to the axis of the steering column. It has 
been noted that the mounted on an angle on the tunnel of the automobile 
also experienced earlier firing time. The study of the plots of 
acceleration data on the two particular vehicle crashes described above 
led to an understanding of this phenomenon. As shown in the FIGS. 6 
through 11, the two crashes in question were at 45 mph, 30 degree angle, 
car-to-car crash where the bullet car struck a target car at the A-Pillar. 
The vehicle of interest was the target car. Since the front of the car 
missed in this crash, the sensor closure time for the crush zone sensors 
is late. The crash therefore, must be sensed by a passenger compartment 
mounted sensor. The second crash of interest is a 9 mph frontal barrier 
which the automobile manufacturer does not want the sensor to fire. When 
any sensor is mounted parallel with the axis of the vehicle the sensor 
would fire late on the A-Pillar crash and also fire on the 9 mph crash. If 
the sensor is designed so that it misses the 9 mph crash, it is even later 
on the A-Pillar crash. And similarly, if the sensor is designed to fire on 
time for the A-Pillar crash it fires even earlier on the 9 mph crash. 
However, when the sensor is placed on a 24 degree angle, the opposite 
occurs. A sensor can easily be designed which does not fire on the 9 mph 
crash but fires in plenty of time on the A-Pillar crash. When a sensor is 
placed on a 24 degree angle as in FIGS. 10 and 11, it is sensitive to 41 
percent (SIN 24.degree.) of the vertical velocity change and loses only 9 
percent (1-COS 41) of the horizontal velocity change. In the A-Pillar 
crash, there is a substantial oscillating vertical velocity change 
component. This, when superimposed on the longitudinal velocity change, 
causes the resultant to also oscillate. The sensor then fires on one of 
the peaks of the combined velocity change oscillation. On the 9 mph crash 
on the other hand, there is no such significant vertical velocity change 
and thus placing the sensor on an angle does not increase its sensitivity 
to this crash. 
Although a passenger compartment mounted system has been described herein, 
it is obvious that many of the advantages of this invention would also 
apply to a crush zone sensor system. 
By indicating that the sensor is to be pointed downwardly, it is understood 
that it is the front, or part closest to the front of the vehicle, of the 
sensor that is meant. 
Although a system for an automobile has been described herein, it is 
obvious that the advantages of this invention would apply to the 
protection of operators and passengers of other types of vehicles, since 
by the term "vehicle" as used herein, it is intended to include trucks, 
boats, airplanes, and trains. 
Airbags are particularly effective in preventing injuries to occupants for 
frontal impacts. They are also effective for side impacts when the target 
car experiences a substantial longitudinal velocity change and the 
occupants would, therefore, be injured by striking the windshield, 
steering wheel, or instrument panel. In a recent study by a major 
automobile manufacturer it was estimated that five percent of all 
accidents where airbags could be of significant help in preventing death 
and reducing injury were side impacts typified by the 45 mph, 30 degree 
A-Pillar impact described herein. It is generally accepted among auto 
companies that it is undesirable to fire an airbag on a low speed impact 
typified by a 9 mph frontal barrier impact. Heretofore, as shown in FIGS. 
6 and 7, it has been impossible to distinguish between these two crashes 
since all crash sensors to date except those mounted on the steering wheel 
have been pointed in a horizontal direction. 
Naturally, the advantage of utilizing the vertical acceleration components 
in conjunction with the horizontal acceleration components could be 
realized through the use of two accelerometers in an appropriate 
electronic circuit. The invention described herein relates to the use of 
the vertical acceleration components present in a vehicle crash to permit 
discrimination between airbag desired and airbag not desired crashes. 
Sensors have been placed on steering columns, and thus are more sensitive 
to the vertical acceleration components. The fact that this improved the 
discrimination ability and the response time of the sensor was not known, 
and thus all other crash sensors in the vehicle have always been placed 
with their sensitive axises in the horizontal plane. 
Thus the forenoted objects and advantages of the invention are most 
effectably 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.