Note: Descriptions are shown in the official language in which they were submitted.
W094/~973 215 0 9 21 PCT~S94/03530
NnLTIPLE-8TRATEGY CRA8H DI8~T~TN~ION ~Y~
~ACKGROUND OF THE INVENTION
The present invention relates to motor vehicle crash
discrimination systems utilized for actuating or deploying a
passenger safety restraint, and more specifically to a system and
a method for actuating a passenger safety restraint which
utilizes detected occupant position to achieve improved
functionality and reliability.
Conventional vehicle crash discrimination systems
typically employ at least one acceleration sensor affixed to the
vehicle for sensing vehicle acceleration. ~he sensor's output
is supplied to a crash discrimination circuit which determines
at least one crash measure, such as a value for vehicle velocity
through integration of the sensor's output over time, for
subsequent c~rArison to a predetermined threshold value. lf the
predetermined threshold value is ~s~ed, the discrimination
circuit outputs a trigger signal which actuates or deploys a
passenger safety ~ raint, such as an air bag or passive seat
belt pretensioning mechanism.
The time at which such an accelerometer-based crash
discrimination circuit actually generates this trigger signal,
relative to the beginning of the crash, is known as the "actual
time to fire;" and a given accelerometer-based crash
discrimination circuit inherently provides a range of such actual
times to fire, as generally determined by the profile of the
crash experienced by the vehicle (sometimes referred to as "crash
type"). Specifically, in the above example, since the relative
- amount of time required in order for the velocity value
(integrated acceleration) to e~c~ the threshold value
nec~s~rily depends upon the individual values for acceleration
data generated by the sensor, and since a severe crash type is
likely to generate higher individual acceleration values than
those generated by a moderate crash type, a given accelerometer-
based crash discrimination circuit is inherently capable of
generating the trigger signal over a range of times relative to
the beginning of the crash.
W094l~973 PCT~S94/03530 -
2~92~
~.
One failing of such conventional accelerometer-based
crash discrimination systems is that they fail to account for
variations in vehicle passenger/occupant conditions (whether
static or dynamic) in determining whether to actuate the safety
restraint, particularly as these variations affect the amount of
time otherwise available for crash discrimination while still
permitting safe and complete actuation/deployment of the safety
restraint. This ~irllm amount of time for crash discrimination
analysis, as measured from the beginning of a crash, is the
"required time to fire" of the safety restraint. More
specifically, conventional accelerometer-based crash
discrimination systems are generally designed to assume a set of
"no~i n~ 1 ~1 occllr~nt conditions, such as the presence within the
vehicle of a 50th-percentile male occupant and the failure of
such an occl~pAnt to wear a seat belt, as well as a fixed required
time to fire.
The use of these assumed '~nomin~ conditions by known
crash discrimination systems tends to ensure proper actuation of
the safety restraint only to the extent that they accurately
describe the actual occupant conditions at the time at which
severe vehicle acceleration (deceleration) is detected by the
accelerometer. Correlatively, the use of this single set of
ACsllmrtions~ with its attendant required time to fire, inherently
causes unnec~ccary~ ill-timed, or perhaps even undesired
actuation of the safety restraint where the assumed conditions
are not otherwise met by the occllpAnt at the time the
accelerometer indicates severe vehicle acceleration, as when
there is no occllp~nt present within the vehicle; or when the
occllp~nt is not a 50th-percentile male; or in marginal crash
situations where a seat belt otherwise provides sufficient safety
protection for the occupant; or in crash situations where the
occllr~nt is improperly positioned relative to the safety
restraint such that actuation of the safety restraint could
itself injure the occllp~nt. Moreover, where the vehicle occupant
to be protected is a front-seat passenger rather than the
vehicle's driver, many additional occupant condition scenarios
are raised, such as that of a child moving around in the seat at
W094/~973 2 ~ ~ 0 9 21 PCT~S94/03530
the start of a crash; or a child moving into the front passenger
seat from a rear seat as a crash begins; or a rear-facing infant
seat positioned only a few inches away from the point of
deployment of the safety restraint; or an adult bending over to
pick something up off the vehicle floor as a crash begins; or a
passenger holding a heavy object near the deployment point; or
a parent holding a child on her lap. Finally, to the extent that
actual occllpA~t conditions indicate a longer required time to
fire, such prior art crash discrimination systems fail to utilize
that additional time for increased decisional reliability, let
alone the additional acceleration information generated during
that additional time.
Another known vehicle crash discrimination system
disclosed in U. S. Patent No. 5,118,134 to Mattes et al utilizes
both ~PncpA vehicle acceleration and the occupant's transitory
displacement from a nominal seating position in determining
whether to actuate a safety restraint. A further ~h~iment uses
sensed transitory occl~p~nt velocity, as measured by the relative
change in detected occupant displacement over time, as a third
trigger criterion. The relative occupant displacement and/or
transitory occupant velocity is measured using ultrasonic, light
or microwave signals as transmitted between fixed transmitters
and receivers mounted either longitudinally or transversely of
the vehicle, with the latter configuration providing an
indication of occllrAnt displacement from his nominal position as
he "breaks" each one of several planes defined by the tra~cAl~sprs
within the passenger compartment. In the preferred embodiment,
the system comrAres the present-sensed vehicle acceleration to
a first threshold value, the relative displacement of the
occupant from his nominal position to a second threshold value,
and the relative velocity of the occupant to a third threshold
value. The safety restraint is actuated when the first threshold
value and either one of the second or third threshold values are
simultaneously P~sPeAed.
While the system disclosed in U. S.
Patent No. 5,118,134 to Mattes et al improves reliability over
conventional accelerometer-based crash discrimination system
W094/~973 ~ 9 2 i PCT~S94/03530 -
through its use of displacement of an occllr~nt from his nominal
position and, perhaps, of transitory occupant velocity
information derived from such occupant displacement, the system
remains relatively rigid due to its reliance upon but a single
set of decisional criteria (the predetermined threshold values
for vehicle acceleration, occupant displacement from nominal and
transitory occupant velocity), as well as the use in the
preferred disclosed embodiment of relatively low-resolution,
noncontinuous occllpAnt position information obtained with the
primary "break-the-plane" transducer configuration. Stated
another way, while the arrangement of Mattes et al attempts to
accommodate gross displacement of the occupant from his nominal
seating position by making such displacement an additional
trigger criterion, the system does not otherwise accQm~odate
various deviations from assumed nominal conditions, including
volitional occ~pAnt movement, which affect the manner in which
other trigger criteria are best utilized for crash discrimination
analysis.
SUMMARY OF THE lNv~NllON
It is an object of the present invention to provide a
system and method for vehicle crash discrimination which uses
data representative of actual oc~lr~nt conditions to optimize its
crash discrimination analysis, thereby achieving increased
efficiency and reliability in controlling actuation of a vehicle
safety restraint such as an air bag.
It is another object of the present invention to
provide a system and method for vehicle crash discriminàtion
which features multiple crash discrimination strategies to
optimize safety restraint efficiency and reliability.
It is another object of the present invention to
provide a system and method for vehicle crash discrimination
which utilizes multiple crash discrimination strategies, each of
which provides a different range of actual times to fire.
A further object of the present invention is to
provide a system and method for vehicle crash discrimination
featuring multiple crash discrimination strategies, at least one
W0941~973 21~ O g 2 i PCT~S94103530
~ _5_
of which uses the detected distance from occupant to fixed
vehicle interior structure in determining an actual time to fire.
It is another object of the present invention to
provide a system and method for vehicle crash discrimination
5 which uses occltpAnt position information to select a preferred
one of a plurality of predetermined crash discrimination
strategies to achieve increased efficiency and reliability in
actuating a safety restraint.
It is another object of the present invention to
provide a system and method for discriminating vehicle crashes
which adjusts the decisional criteria used for determining an
actual time to fire based on the detected distance between the
occ~lr~nt and a potential impact point within the vehicle, or
based on occ~rAnt condition data (itself derived from detected
distance).
It is another object of the present invention to
provide a system and method for discriminating vehicle crashes
which determines the distance between a vehicle occupant and a
potential impact point within the vehicle, and utilizes this
information both for selecting the optimal discrimination
strategy and as an additional criterion used by the selected
strategy in determining an actual time to fire.
It is yet another object of the present invention to
provide a system and method for discriminating vehicle crashes
which utilizes an optical low-threshold acceleration sensor to
cAl;hrate an optical occupant-position sensing means, to
discriminate irrelevant occnpAnt movement from movement caused
by crash situations, and to generate an output signal
representative of vehicle acceleration.
Under the present invention, a system for actuating a
vehicle safety restraint comprises means for detecting a distance
between a vehicle occupant and a fixed structure within the
vehicle; means responsive to the detecting means for generating
occ~-p~nt condition data representative of transitory occupant
position, transitory occupant velocity and/or transitory occupant
acceleration; and means for receiving information representative
of instantaneous vehicle acceleration. The present system
W094/~973 ~ 9 21 PCT~S94/03530
further comprises processor means responsive to the detected
distance and the received vehicle acceleration information for
determining a first actual time to fire with which to control
actuation of the safety restraint. Specifically, the processor
means continuously generates occupant condition data based on the
detected distance, with the occupant condition data being
representative of at least one of the group consisting of
transitory o~-cl~pAnt position, transitory occupant velocity and
transitory occupant acceleration. The processor means further
selects one of a plurality of crash discrimination strategies for
use in a crash discrimination analysis based on the generated
occl~Ant condition data, with each of the crash discrimination
strategies using received vehicle acceleration information to
provide a range of actual times to fire, and with the range of
actual times to fire provided by one of the strategies being
different from the range of actual times to fire provided by
another of the strategies. The proc~or means uses the selected
strategy to determine the first actual time to fire needed for
col.LLolling actuation of the restraint. Finally, the present
system includes means responsive to the processor means for
actuating the safety restraint at the thus-determined first
actual time to fire.
In accordance with the present invention, a method for
actuating a vehicle occupant safety restraint comprises the steps
of detecting a distance between a vehicle occupant and a fixed
structure within the vehicle; generating occupant condition data
based on the detected distance, where the generated occupant
condition data is one of the group consisting of transitory
occllrAnt position, transitory occllr~nt velocity and transitory
occupant acceleration; receiving information representative of
instantaneous vehicle acceleration; and selecting one of a
plurality of crash discrimination strategies for use in a crash
discrimination analysis based on generated occupant condition
data, wherein each strategy uses received vehicle acceleration
information to provide a range of actual times to fire, with the
range of actual times to fire provided by one of the strategies
being different from the range of actual times to fire provided
W094/~973 PCT~S94/03530
9 2 ~
by another of the strategies. The present method further
comprises the steps of determining an actual time to fire in
accordance with the selected strategy; and actuating the safety
restraint at that actual time to fire. Through its selection of
crash discrimination strategy based upon data representative of
actual o~ nt conditions--whether the data is representative
of a static occl~Ant condition such as transitory occupant
position, or a dynamic occupant condition such as transitory
ocrl~rAnt velocity or transitory occ~rAnt acceleration--the
present method correlatively adjusts the time period allotted for
such crash discrimination analysis to provide additional time for
discrimination analysis only when actual occupant conditions
indicate that such additional time is available, and to use less
time when actual occ~r~nt conditions indicate that a trigger
decision is needed in a shorter time period after the
commencement of a collision.
More specifically, under the present invention, the
individual crash discrimination strategies utilize either
uniquely-different parameter-based algorithms; identical
parameter-based algorithms employing one or more dissimilar
critical thresholds; or both. Thus, in one disclosed embodiment,
the multiple strategies are defined using a single parameter-
based algorithm employing at least one critical threshold which
varies as a function of detected occl~rAnt distance. And, under
the present invention, the detected occ~r~nt distance and/or the
occupant condition data generated therefrom (i.e., transitory
occ~pAnt position, velocity and/or acceleration) may be further
used as decisional parameters in one or more crash discrimination
strategies.
Accordingly, the present method may further include the
steps of comparing the detected occupant distance to a first
predetermined threshold value in at least one of the crash
discrimination strategies, and determining an actual time to fire
in accordance with that strategy only when and if the detected
distance exceeds the first threshold value. Or the present
method may include the steps of comparing generated data
representative of transitory occupant velocity to a second
W094/~973 21~ Q 9 21 PCT~S94/03530
predetermined threshold in~accordance with one or more crash
discrimination strategies, and determining an actual time to fire
in accordance with that strategy only when and if the transitory
oc~llp~nt velocity exceeds the second threshold value. Or the
present method may include the steps of comparing generated data
representative of transitory occupant acceleration to a third
predetermined threshold in accordance with one or more crash
discrimination strategies, and determining an actual time to fire
in accordance with that strategy only when and if the transitory
occl~r~nt acceleration the transitory occllp~nt acceleration
P~c~e~c the third threshold value. Finally, as noted above, the
present method may include the additional steps of adjusting the
second and third threshold values to which the data
representative of transitory occl~r~nt velocity and transitory
occl~p~nt acceleration are respectively compared based on the
detected distance between the occupant and fixed vehicle
structures, in real time. As noted above, the transitory
oc~lpAnt velocity and/or the transitory occupant acceleration are
~hP~cPlves dynamic occupant conditions and, hence, may further
be used as criteria for selecting the crash discrimination
strategy which provides the optimal protection for the occupant.
In aGcordance with the present invention, the
generation of occupant condition data from detected distance
increases the overall efficiency and reliability of the system
by customizing the discrimination analysis in real time to match
actual conditions of a vehicle occupant. Thus, the present
invention contemplates relatively high-speed or essentially
"continuous" analysis of actual occupant conditions, as
exemplified by transitory relative occl~pAnt position within the
vehicle, so that the optimal crash discrimination strategy is
selected and, hence, will be employed at the time of the vehicle
collision to provide m~imllm protection for vehicle occupants.
Specifically, the distance between the occupant and fixed vehicle
structure is detected by transmitting a beam of light at a
designated area within the vehicle potentially occupied by a
person, measuring a relative intensity level, or average of two
scattering angles of at least a portion of the light beam which
W094/~973 ~ 1 5 ~ 9 ~ 1 PCT~S94/03530
is reflectively scattered by a surface within the designated
area, and determining the distance between the scattering surface
and a fixed structure within the vehicle based on the measured
intensity level. In a first ~ho~ nt, the distance is detected
by measuring the intensity level of the reflectively scattered
light beam received at two different locations separated by a
predetermined distance, and determining the distance between the
scattering surface and the fixed structure based on a ratio of
the intensity levels measured at the two different locations.
In another embodiment, the distance between the
scattering surface and the fixed structure is detected by
transmitting the beam of light from a first location within the
vehicle. A detector having a predetermined angle of light
detection is positioned at a second location within the vehicle.
The first and second locations are separated by a predetermined
distance. The reflectively scattered light beam is focused by
a lens to form a spot within the light detection area of the
detector, wherein the location of the spot is indicative of the
angle from which the light is received. The location of the spot
within the light detection area is determined using a
photosensitive device with a set of outputs that indicate spot
position. The distance between the scattering surface and the
fixed structure is then determined by the angle from which the
light is received.
A further embodiment of the present invention utilizes
an optical low-threshold safing sensor to provide calibration of
the system, ~icc~rn irrelevant occ~lp~nt movement, and generate
data representative of vehicle acceleration. At least a portion
of the transmitted light beam is directed at a first end of an
inertial sensing mass located within the safing sensor. The
first end comprises a material having known reflectivity. The
inertial sensing mass moves from a first position to a second
position within the sensor in response to an acceleration force.
Movement of the inertial sensing mass from the first position to
the second position is detected based on a measured intensity
level of the light reflectively scattered by the first end of the
inertial sensing mass. Detection of the inertial sensing mass
W094/~973 PCT~S94/03530 -
21~Q~21
--10--
movement generates information representative of instantaneous
vehicle acceleration.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of motor vehicle
crash discrimination system having an occ~ nt position detector
in accordance with the present invention;
FIG. 2 is a schematic illustration of a first
embodiment for detecting the occupant position;
FIGS. 3a, 3b and 3c are schematic illustrations of a
second embodiment for detecting the occupant position;
FIGS. 4a, 4b and 4c are schematic illustrations of a
third embodiment for detecting the occupant position;
FIG. 5 is a schematic illustration of a fourth
embodiment for detecting the occupant position based on the
second and third embodiments shown in FIGS. 3a-3c and
FIGS. 4a-4c;
FIGS. 6a and 6b illustrate plots of occupant position
data over time for irrelevant occ~rAnt movement and for occupant
movement responsive to a vehicle crash, respectively;
FIG. 7 is a s~h~m~tic illustration of a further
embodiment of the vehicle crash discrimination system having an
optical low threshold safing sensor;
FIG. 8 is a plot of Strategy versus Time illustrating
the range of actual times to fire provided by exemplary discrete
crash discrimination strategies R, S, T, X and Y, as might be
obt~;nP~ where each strategy employs uniquely-different
parameter-based algorithms in determining an actual time to fire;
and
FIG. 9 is a plot of Strategy versus Time illustrating
the ranges of actual times to fire provided by exemplary crash
discrimination strategy Z, which employs a critical decisional
threshold which varies as a function of the detected distance
between the occ~ nt and a fixed structure within the vehicle.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S~
Referring to FIG. 1, there is shown a vehicle crash
basic occl-r~nt condition discrimination system 10 in accordance
with the present invention which senses various occupant
-
W094/~973 21~ O 9~1 PCT~S941Q3530
--11--
conditions and thereafter selects the optimal one of a plurality
of predetermined crash discrimination "strategies" for use in
triggering a vehicle occupant safety restraint, such as an air
bag 38, based upon sPn~ oc~pAnt conditions. Specifically, the
system 10 comprises an active infrared position detector 12
comprising a ~o~ tor 14 connected to an optical transmitter 16,
and an optical receiver 18 connected to a synchronous
demodulator 20. The demodulator 20 generates an output 22-
indicative of the distance between an oc~-pAnt 24 and a potential
impact point within the vehicle. The output 22 is supplied to
a signal processor/discrimination unit 26 for storage in a
memory 36, and for subsequent use as a basis for selecting the
t~mrorally most appropriate or "optimal" one of a plurality of
predetermined crash discrimination strategies. The output 22
preferably further forms the basis for at least one decisional
criterion or "parameter" used by at least one of the available
crash discrimination strategies.
Specifically, in response to analysis of the detected
distance between the occupant and a fixed interior structure of
the vehicle, the processor/discrimination unit 26 generates
occllp~nt condition data, such as transitory values for occupant
position and occllrAnt velocity, with which to further select the
optimal crash discrimination strategy to be used in controlling
deployment of the air bag 38, as communicated to the safety
restraints via at least one ouL~uL line 28; and/or to control
activation of an audible or visual warning device(s) 40 via at
least one output line 30 for alerting the vehicle occupant 24 to
a potentially hazardous seating condition. The infrared position
detector 12 and the signal processor 26 receive power from a
vehicle battery 32.
The system 10 is fixedly mounted on and/or in the
vehicle steering column or dashboard. Thus, in a crash, the
fixedly-mounted portions of the present system 10 will experience
essentially the same decelerations as a conventional
accelerometer. However, an occupant's motion or reaction to a
crash will be somewhat different from the motions of the
structures upon which the accelerometer is mounted, since the
WO9~/~973 ~ 9 2 ~ PCT~S94/03530
-12-
vehicle occupants are not rigidly affixed to any cabin structure.
Accordingly, the pattern of relative motions of the mounting
structures and the vehicle occupant(s) is used by the present
system and method as a primary input for selecting the optimal
one of the available predetermined crash discrimination
strategies providing the decisional criteria with which to
analyze a crash, and as a secondary input to at least one of the
strategies as a crash discrimination criterion (or to form the
basis from which another criterion is derived).
Accordingly, under the present invention, the system 10
measures the distance of the occupants relative to the fixed
structure within the vehicle and generates transitory values for
occllpAnt position and velocity therefrom. As will be described
more fully hereinbelow, advanced signal processing techniques
performed in the processor/discrimination unit 26 will allow
identification of those situations where deployment of a safety
restraint is required. Through analysis of dynamic occupant
conditions such as transitory occupant velocity (as generated
from changes in ~he detected distance to the oc~Ant over time),
the system 10 is further able to recognize or identify occupant
motion characteristic of seat belt usage and to distinguish this
type of motion from occupant motion where no seat belt is being
used. Such occllpAnt motion recognition/identification also
enables the present system 10 to distinguish "irrelevant" or
otherwise inconsequential occupant motions such as a hand or arm
moving through the incident beam.
The reaction of the vehicle as derived from
accelerometer data preferably still forms the basis for at least
one decisional criterion found in each of the available crash
discrimination strategies. However, as noted above, the detected
occllrAnt distance and/or the occupant condition data generated
therefrom are preferably also used as decisional criterion in one
or more of the available crash discrimination strategies.
In operation, a narrow infrared beam 34 is directed
horizontally at the expected position of the driver or passenger.
At least a portion of the light energy scattered by the
occll~Ant's clothing is detected by receiver 18, which is located
-
W094/~973 PCT~S94/03530
~1~092~
away from the beam axis so that the receiver 18 can detect
differences in reflected light intensity and angle associated
with oc~lrAnt absence, presence and forward motion. The infrared
beam 34 is distinguished from ambient light of the same
wavelength by modulating the signal 34. ~ modulation frequency
of about 10 Khz or higher provides acceptable modulation since
a minimum of 10 Khz is well within the range of most existing
electronic and optical systems, and is fast enough to monitor
passenger movement in real time. Determination of the
instantaneous distance of the occ~lrAnt from the transmitter 16
is based on the relative intensity of the light scattered by the
occupant as measured by a detector or detectors, with
measurements based on relative intensity or the angle from which
the light is received.
Referring to FIG. 2, a first ~ho~ nt 100 of a
transducer for detecting the relative distance of an occupant
employs the principle that the intensity of scattered light is
inversely proportional to the square of the distance r from
scattering surface to the receiver 18. In the first
e~hoA;ment 100, the receiver 18 comprises a pair of photodiode
detectors 102 and 104 situated a known distance apart and placed
at different distances from the point where the incident light
is reflectively scattered. The receiver 18 is preferably
positioned relative to the transmitter 16 so as to produce a
relatively small angle ~ between the transmitted beam 34 and the
portion of the reflected beam impinging upon the receiver 18.
In order to insure that the two photodiode detectors 102 and 104
are sensing light scattered from the same area, a beam
splitter 108 will be used to direct half of the reflectively
scattered light to one photodiode, and half to the other. The
use of a beam splitter also serves to eliminate any angular
variations within the plane of incidence. This helps to insure
that the difference in distance is the only factor that affects
the relative intensities of the light received by the
photodiodes.
The structure of receiver 18 further comprises light
passages 110 and 112 having light absorbing walls 114 for
W094/~973 ~ 9 21 PCT~S94/03530 -
-14-
coupling the beam splitter 108 with detectors 102 and 104. The
light absorbing walls 114 may further include baffling to further
reduce light reflected to the detectors 102 and 104. The
incident light beam 34 can be generated by a light emitting diode
or semiconductor laser 116 located within the transmitter 16,
with the generated light being subsequently collimated by a
lens 118 to produce a light beam 34 that maintains a constant
diameter of approximately one inch over a distance of 6 to 30
inches. The collimated beam 34 is then scattered in all
directions by a reflecting surface 120, i.e., the vehicle
occupant 24 if present.
Suppose that the distance between detectors 102
and 104 is L, and the distance from the point of reflective
scattering to the closest photodiode 102 is x. Under the
principle of 1/r2, the intensity of the scattered light at the
closer detector 102 is p~ O~UL Lional to l/X2~ and the intensity of
the scattered light at the other detector 104 is proportional
to 1/(x+L) 2. If the field of view is the same for both
detectors, then:
Il (x+L) 2 _ x = . L
I2 x2 (I2)
Thus, the ratio of the intensities sensed by the two photo-
diodes 102 and 104 serves as a measure of the distance x to the
vehicle occupant.
It is noted that the l/r2 relationship holds true only
for light that is randomly scattered from an object. The
intensity of light that is spPc~ rly reflected does not diminish
as a function of distance in the same way as scattered light.
Fortunately, the specularly reflected light can be screened out
by using polarizers. Since specularly reflected light tends to
retain the polarization of the incident light, the incident light
can be polarized in a particular direction, e.g., vertical, and
the reflectively scattered light can be polarized in the
complementary direction (horizontal). Because the reflectively
scattered light is randomly polarized, polarization of the
W094/~973 215 0 9 21 PCT~S94/03530
-15-
scattered light should permit about half of the light intensity
to reach the detectors 102 and 104.
Referring to FIGS. 3a-c, there is shown a second
embodiment 200 for determining the position of an occupant based
on triangulation of the received light intensity. Elements
previously described have like reference numbers. More
specifically, the collimated beam 34 which is scattered in all
directions by the reflecting surface 120, i.e., the occupant, is
focused by an imaging lens 202 to form a relatively small
spot 204 on a Bi-cell detector 206. As shown in FIG. 3b, the
Bi-cell detector 206 comprises a pair of adjacent photodiode
detectors 208 and 210. Since the lens 202 aperture selects the
fraction of the scattered light that reaches the detector 206,
the spot 204 on the detector moves when the angle x between the
axis of beam 34 and the axis of the reflectively scattered light
reaching the detector changes, as shown in FIG. 3c.
The direction of the reflected rays reaching the
photodiode detectors 208 and 210 is determined by the positions
of the center of the imaging lens 2 02 and the point where the
reflecting surface 120 cuts the incident beam 32. Thus, the
particular angle ~ at which light is received at the
photodiodes 208 and 210 depends only on the distance x to the
reflecting surface. This angle is determined by tan ~ = b/x,
where x is the distance from the source to the reflecting
surface, and b is a predetermined lateral separation of the
transmitter and the detector. As the angle x varies, the
relative amounts of radiant flux received by the two diodes 208
and 210 also varies. The diodes 208 and 210 generate respective
current outputs I~ and I2 proportional to the relative amounts of
light received by the diodes. Signal processing of the detector
ouL~uL currents preferably includes the step of calculating the
amplitude-independent ratio of currents to correct for reflection
variation at the scattering surface 120. The ratio of the
relative intensities determines the location of the spot 204 to
provide a good measure of the angle and, hence, of the distance
x to the reflecting surface 120.
_
W094/~973 PCT~S94/03530
2~5~921
-16-
Referring to FIGS. 4a-c, there is shown a third
embodiment 300 for determining the position of an occupant which
employs triangulation of the received light intensity similar to
embodiment 200, but which replaces the Bi-cell detector 206 with
5a position sensitive detector (PSD) 302. The PSD 302, as shown
in FIG. 4b, is a distributed photosensitive device for which the
contrast ratio (I~-I2)/(I~I2) in output currents I~ and I2 from
the top and bottom ends 304 and 306 provides a linear measure of
the spot's vertical position. As shown in FIG. 4c, when the
angle x varies, the position at which the reflected light is
imaged will vary across the PSD 302. The ratio of the two
current outputs I~ and I2 varies as the center of light intensity
moves across the PSD 302 and, therefore, provides a measure of
the angle . The distance x to the occupant 24 can then be
determined in a like manner as embodiment 200, described
hereinabove.
As shown in FIG. S, a second receiver 308 having a
Bi-cell detector or PSD 310, and a imaging lens 312, can be
located on the opposite side of the collimated incident beam 34
20from the first Bi-cell detector 206, or PSD 302. The arrangement
shown in FIG. 5 can provide a more accurate detection of the
occll~Ant's position because the use of the additional
receiver 308 located on the opposite side of the incident beam 34
compensates for shifts in the scattering angle caused by
variations in reflectivity across the incident beam. More
specifically, variations in reflectivity of the reflecting
surface shift the center of the reflectively scattered light beam
from the geometric center of the light beam. The shift in the
center point can change the angle of the received light beam.
The use of two separate receivers located on opposite sides of
the incident beam allows the system 10 to make an accurate
determination of distance despite any shifts in the center of the
reflectively scattered light beam.
In accordance with the present invention, the present
system 10 uses the occupant distance information provided by the
optical position detector 12 in several ways: for selecting the
optimal crash discrimination strategy, as a decisional criterion
W094/~973 2 ~ 5 Q 9 21 PCT~S94/03530
within one or more strategies, and/or for adjusting other
decisional criteria (e.g., thresholds) used to evaluate other
- decisional parameters in one or more strategies. Specifically,
the occl~pAnt distance information provided by optical position
detector 12 can be stored and subsequently tracked relative to
the fixed vehicle interior structure by the signal processor 26
to generate data which approximates such actual occupant
conditions as occupant presence, occupant velocity (change in
occl~pAnt distance over a period of time), occupant acceleration
(change in occupant velocity over a period of time), and various
occ~pAnt seating conditions, e.g., distance from potential
impacts points such as the steering wheel or dashboard, occupant
in a potentially dangerous position relative to the potential
impact points, and ocr~pAnt use of a seat belt. For example, the
latter determination seat-belt use can be reliably predicted
under the present invention based on the pattern of occupant
motion, i.e., analysis of the transitory occupant position and
velocity.
Also, since the processor 26 stores and tracks the
position information with respect to time, irrelevant occupant
movements, such as hand waving, arm movement, etc., can be
differentiated from movement caused by a crash situation. This
is illustrated in FIG. 6a, which shows a plot of occupant
position-versus-time data representative of an arm waving, and
FIG. 6b, which shows a plot of data representing an occupant
during a crash situation. m erefore, with the present invention,
the vehicle crash discrimination system lO is designed to provide
high frequency measurements of the position of the driver and/or
passengers relative to potential impact points such as the
steering wheel and dashboard, and to process that information so
as to optimize the safety restraint deployment decision. The
system can therefore refrain from deploying an air bag when an
ocrllpAnt is too close, where the explosive force with which an
air bag is inflated might otherwise do substantial harm. Thus,
the present invention can prevent injuries by refraining from
deploying the air bag. The further alternative of adjusting the
resulting air bag inflation profile, for example, upon or
PCT~S94/03530 -
W094/~973 ~ 1 5 ~ 9 ~ I
-18-
subsequent to deter~i~ ~f an actual time to fire using the
multiple strategy system and method of the present invention, is
taught in co-pending U. S. Patent Application No. 08/182,281
filed January 14, 1994, and entitled "Variable Inflation System
For Vehicle Safety Restraint.
The system lO also measures the actual transitory
position, velocity, and acceleration of the occupants relative
to the potential impact points within the vehicle, and, using
these measurements in conjunction with advanced signal processing
te~hn;ques, the present invention greatly increases the amount
of information useful in the deployment decision. The present
invention also significantly improves the crash discrimination
analysis by supplying vehicle oc~lrAnt position information which
can be used in real time to adjust decisional criteria through
continuous selection of the optimal crash discrimination strategy
in real time, with their differing ranges of actual times to
fire. The on-going ability to switch between available
discrimination strategies in response to changing occupant
conditions allows the present system lO to transitorily customize
the decisional criteria used for triggering deployment of the air
bag 38 and, hence, maximize occupant protection notwithstanding
those changing conditions.
Further, by selecting between the different available
crash discrimination strategies, each with their individualized
decisional criteria and available range of actual times to fire,
the crash discrimination analysis is effectively adjusted in
light of actual occl~pAnt conditions to improve the efficiency of
the discrimination analysis and the reliability of any necessary
actuation of the safety restraint. The effect of strategy
selection on actual times to fire under each of the two
"approaches" for providing multiple crash discrimination
strategies is shown in FIGS. 8 and 9, respectively.
Specifically, FIG. 8 is a plot of Strategy versus Time
illustrating the range of actual times to fire provided by
exemplary discrete crash discrimination strategies R, S, T, X
and Z, as might be obtained where each strategy employs a
uniquely-different parameter-based algorithm in determining an
~ W094/~973 PCT~S94/03530
21~0~21
--19--
actual time to fire. That each -given parameter-based crash
discrimination strategy inherently provides a range of actual
times to fire may be seen from the following simplified example:
assuming a crash discrimination strategy which determines a need
to actuate an air bag at an actual time to fire TTF, if a
velocity term derived from vehicle acceleration data exceeds a
fixed 14 mph threshold value, the actual time to fire TTF~
nonetheless remains dependent upon the amount of time it takes
for the velocity term to ~ceP~ the 14 mph threshold. Since the
velocity (integrated acceleration) term will accumulate faster
in a relatively severe crash, with its higher individual
transitory acceleration values, the actual time to fire TTF~ in
a relatively severe crash will occur at an earlier absolute time,
as measured from the beginning of the crash. In contrast, in a
relatively moderate (but still significant) crash, the velocity
term will accumulate more slowly, with its relatively lower
individual values for transitory vehicle acceleration, with the
resulting actual time to fire TTF~ occurring at a later absolute
time relative to the beginning of the crash. Stated another way,
an acceleration-based crash discrimination algorithm typically
provides a range for actual times to fire, with any given set of
acceleration data (which may itself loosely be said to define a
crash type) resulting in generation of a trigger signal at an
actual time to fire within that provided range of actual times
to fire.
FIG. 9 is a plot of Strategy versus Time illustrating
the ranges of actual times to fire provided by exemplary crash
discrimination strategy Z, which employs a critical decisional
threshold which varies as a function of the detected distance
between the occupant and a fixed structure within the vehicle.
The resultant "band" shown in FIG. 9 may be appreciated as an
infinite number of discrete strategies located between two
constructive "boundary" strategies Z~ and Z2~ each providing their
corresponding range of actual times to fire.
The above concepts may be further understood in light
of the following examples: in a first exemplary situation,
wherein a vehicle occupant wearing a seat belt experiences a
W094/~973 PCT~S94/03530 -
2150~21
-20-
marginally-low-velocity crash, occupant position and occupant
motion is analyzed in real time to conclude that the occupant is
indeed wearing a seat belt. Since the seat belt prevents the
oc~lp~nt from striking any interior structures within the vehicle
with injury-causing force, deployment of the air bag in this
situation is unnec~sA~y and undesired. Accordingly, as the
degree of confidence in the determination of seat-belt usage
increases (e.g., given an essentially static occupant condition),
the selected strategy will have an increasingly high range of
actual times to fire, to the point that an actual time to fire
with which to deploy the air bag will not be determined, from a
practical perspective. Stated another way, the selected crash
discrimination strategy would likely feature heightened threshold
values when the system 10 detects an occupant condition
indicative of seat-belt usage, thereby providing a range of
relatively longer (up to infinity) actual times to fire. This,
in ~ollL.~st with prior art systems, which typically do not
receive any information concerning the actual motion of the
occltpAnt (or lack thereof), whereupon the system must make a
"worst-case" assumption, i.e., no seat belt usage, and deploy the
air bag.
In a second situation, a driver has assumed a position
within the vehicle which is closer to the steering wheel than the
"norinAl position" which would be assumed by a 50th-percentile
male occltp~nt but is otherwise outside the air bag's inflation
zone. The resulting required time to fire--the amount of time
available within which to trigger deployment of the air bag
before the driver enters the inflation zone--is less than the
"nominal" required time to fire for such a 50th-percentile male
occ~tpAnt sitting in the nominal position. By measuring the
actual distance to the driver and generating occupant condition
data therefrom, the present invention selects the crash
discrimination strategy which provides a range of actual times
to fire likely to result in earlier deployment of the air bag
and, hence, prevent the driver from hitting the steering wheel
and/or prevent injury to the driver which might otherwise occur
when inflating the air bag. Stated another way, the selected
~ W094/~973 21 S 0 9 21 PCT~S94/03530
-21-
crash discrimination strategy would likely feature reduced
threshold values when the system lo detects an occ~lpAnt condition
wherein the driver is sitting closer than the otherwise-assumed
nominal or "average" distance from the steering wheel, thereby
providing a range of relatively shorter actual times to fire.
In a third situation, a driver is sitting at a
somewhat-greater-than-average distance from the steering wheel.
Since the driver can then move a greater distance in response to
a vehicle collision before striking any potential impact point
within the vehicle, with the attendant increase in the amount of
time between the commencement of a crash and any such impact, the
required time to fire is correlatively lengthened, thereby
providing additional time and data for use in crash
discrimination analysis. The ability to analyze more information
over a longer period of time in turn provides a more reliable
discrimination analysis. Accordingly, under the present
invention, where an increased distance is detected between the
driver and the potential impact point within the vehicle, the
resulting occ~lr~nt condition data generated from the detected
distance is used to select the crash discrimination strategy
which provides a range of actual times to fire likely to result
in later deployment of the air bag, p~rh~pc through use of a more
"statistically robust" but time-consuming crash discrimination
algorithm. Stated another way, the selected crash discrimination
strategy would likely feature increased threshold values relative
to those employed when the driver is seated the otherwise-assumed
nominal or "average" distance from the steering wheel, thereby
providing a range of relatively longer actual times to fire.
FIG. 7 shows a further embodiment of the passenger
condition discrimination system 10 of the present invention
incorporating a supplemental optical, low-threshold safing
sensor 400. The safing sensor 400 comprises a housing 402 having
a cylindrical passage 404 formed therein, and a magnetic sensing
mass 402 in the passage 404 which is magnetically biased by a
magnetically permeable element 408 to an initial position against
a stop element 410 located at a first end within the passage 404.
The sensing mass 406 is displaced in response to acceleration of
W094/~973 ~ PCT~S94/03530
the housing 402 from the initial position to a second position
within the passage when such acceleration overcomes the magnetic
bias on the sensing mass. Damping means such as an electrically
conductive ring 412, for example a copper tube, encompasses the
passage 404 to provide magnetic damping for the sensing mass 406
during the displacement of the magnetic sensing mass within the
passage 404. The magnetic sensing mass 406 of safing sensor 400
functions in a manner similar to the magnetically-damped,
testable accelerometer as taught in commonly assigned U. S.
Patent No. 4,077,091 to Behr.
As shown in FIG. 7, a portion of the collimated
incident beam 34 is supplied by suitable optical coupling
structure such as a beam splitter 414 and mirror 416, or
alternatively a fiber optic cable, to a second end of the
passage 404. The collimated incident beam is horizontally
redirected down the passage 404 where the beam is reflectively
scattered by a scattering surface 418 of known reflectivity,
e.g., cloth, affixed to an end face of the sensing mass 406. A
receiver 420 comprising an infrared detector 422 and synchronous
demodulator 424 is positioned relative to second end of the
passage 404 so as to receive at least a portion of the
reflectivity scattered light. The distance d of the sensing
mass 406 relative to the fixed incident light source can be
calculated by detecting the intensity of the scattered light as
described her~;nAhove with respect to FIGS. 2-4. The data
obt~;n~ by the synchronous demodulator 424 is provided as 2n
output 426 to the signal processor/discrimination unit 26 for
storage and/or analysis.
The safing sensor 400 of the present invention
provides several advantageous functions for the present vehicle
crash discrimination system 10. First, the safing sensor 400
provides a way of calibrating the system 10. The intensity of
the light scattered by the sensing mass 406 while at the initial
position will be substantially constant, thereby allowing
corrections or adjustments to the transmission of the incident
light beam 34. Further, since the scattering surface 418 affixed
to the end of the sensing mass 406 has a known reflectivity, the
=~
~ W094/~973 215 ~ g 21 PCT~S94/03530
-23-
system 10 will be able to detect a condition where an occupant
is providing a low reflection of the incident beam 34, such as
an occ~lp~nt wearing a material of low reflectivity like black
velvet, based on a comparison of the respective outputs 22
and 426. Thus, the system 10 can make appropriate corrections
for the occllrAnt's low reflectivity.
Second, the safing sensor 400 supplements the signal
processor/discrimination unit 26 in discerning irrelevant
occupant movement, such as a hand-waving in front of the
receiver 18. The signal processor 26 may detect movement of the
occllr~nt because of the data generated by receiver 18. However,
if the sensing mass 406 in the safing sensor 400 does not move,
the signal procPC~or 26 can assume that the oc~lpAnt movement was
not in response to vehicle acceleration.
Third, the safing sensor 400 provides additional data
for use in the discrimination analysis since the data generated
at o~L~uL 426 in response to the movement of the sensing mass 406
can be differentiated twice with respect to time to determine
vehicle acceleration. Vehicle acceleration data can then be
utilized with the occupant condition/position data in the
selected strategy's parameter-based algorithm to provide more
reliable crash discrimination and safety restraint actuation.
Preferably, the distance measurement of the sensing
mass 406 movement should be based on how a frictionless sensing
mass would react to vehicle acceleration. However, as described
her~;nAhove, the safing sensor 400 employs both biasing and
damping of the sensing mass 406 to permit the sensor 400 to be
unaffected by conditions such as very-low-threshold crashes and
rough-road conditions. The biasing and damping of the sensing
mass 406 provides inexact motion measurement data for signal
proc~Ccor unit 26. The effects of the biasing and damping on the
sensing mass movement are well understood, and, therefore, in the
present invention, the signal processor unit 26 preferably
modifies the data from output 426 with a factor which effectively
"undamps" the data before use in the discrimination analysis.
Thus, a movement measurement based on a "frictionless" sensing
mass is obtainable with the above-described safing sensor 400.
W094/23973 PCT~S94/03530 ~
2 ~ 2 ~
-24-
While the preferred embodiments have been described
using an active infrared position detector 12, it will be
appreciated that an acceptable alternative active or passive
sensing arrangement utilizing ultrasonic sensors or microwave
sensors could be employed. It will be further understood that
the foregoing description of the preferred embodiment of the
present invention is for illustrative purposes only, and that the
various structural and operational features herein disclosed are
susceptible to a number of modifications without departing from
the scope of the subjoined claims.
