Dual, independent sensor vehicle impact detectin system

A vehicle impact detection system (10) for controlling the actuation of an occupant safety restraint device includes a dual, independent sensor arrangement (12) having a vibratory sensor (24) affixed to an outer surface (16) of the vehicle for continuously generating an output signal (14) representative of the condition of the outer surface, and a processor (22) for performing signal processing on the output signal (14) to predict the time at which a second crush sensor (26) will produce an output signal (18). The system (10) allows a single point outer surface sensor to reliably predict severe impacts within a few milliseconds of initial impact, and therefore is particularly suited for controlling the actuation of a safety restraint device in response to side impacts.

BACKGROUND OF THE INVENTION 
The present invention relates generally to a vehicle crash discrimination 
system for controlling deployment of a passenger safety restraint device, 
such as an air bag. 
Conventional vehicle crash discrimination systems are primarily designed to 
protect vehicle occupants from frontal collisions. Frontal collision 
detection systems tend to employ sensors which use an inertial sensing 
mass to detect deceleration of the vehicle. Because of the distance 
between the vehicle occupants and frontal impact points on the vehicle, 
conventional inertial sensors provide satisfactory results when a 
deployment decision can be made at least 30-40 milliseconds after the 
initial impact. 
However, conventional crash discrimination systems are simply inadequate 
when deployment decisions must be made within a few milliseconds, such as 
in side impacts. To accommodate this severely restricted decisional time 
period, known side impact detection systems rely on one of three sensor 
arrangements: a contact switch or crush sensor, a pressure transducer, or 
a modified silicon (inertial mass) accelerometer. Examples of such sensor 
arrangements can be found in U.S. Pat. No. 4,995,639 to Breed, U.S. Pat. 
No. 4,966,388 to Warner et al, U.S. Pat. No. 5,202,831 to Blackburn et 
al., U.S. Pat. No. 5,277,441 to Sinnhuber, and U.S. Pat. No. 5,231,253 to 
Breed et al. 
While each one of these known sensor arrangements are more suitable than a 
modified conventional frontal crash discrimination system for side impact 
situations, each known arrangement suffers from inherent drawbacks. For 
example, contact switches only provide a one bit binary output (i.e., "on" 
or "off") which are typically based on the exceeding of a certain 
threshold of force. These thresholds must be carefully adjusted to allow 
the system to differentiate severe crashes from situations like door 
slams, opening of the door into a pole, etc. Pressure transducers only 
provide an output which is responsive to total force across the entire 
surface without being able to distinguish or isolate the force at 
different locations on the surface. Silicon accelerometers are only able 
to typically provide a very limited number of data samples within the 
allowed decision period, and therefore do not provide enough information 
to make reliable decisions. Furthermore, none of these known arrangements 
are suitable for reliably predicting the occurrence of a severe surface 
impact so that the safety restraint device can be actuated as early as 
possible. 
One significant solution to the above-noted deficiencies with the prior art 
is disclosed in a commonly assigned, copending U.S. patent application, 
Ser. No. 08/207,279, filed on Mar. 7, 1994, entitled "Vehicle Impact 
Detection System," wherein a vehicle impact system is formed by affixing 
an array of sensors to an outer surface of the vehicle. The sensor array 
continuously provides a two dimensional output representative of the 
condition of the outer surface to a processor circuit tracking and 
analysis via advance array signal processing. 
While this arrangement successfully overcomes the problems of the prior art 
side impact detection systems, servicing of the multiple surface sensor 
array will typically involve replacement of the entire affected outer 
surface area of the vehicle. Thus, the cost, time, and complexity of 
servicing of the impact detection system could be undesirably high. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to provide a vehicle 
impact detection system which can reliably predict the need to deploy an 
occupant safety restraint within a few milliseconds of an initial vehicle 
impact. 
Another object of the present invention is to provide a vehicle impact 
detection system for controlling actuation of an occupant safety restraint 
device which can reliably predict and differentiate severe vehicle side 
impacts from minor side impacts. 
A further object of the present invention is to provide a vehicle impact 
detection system which utilizes a single point outer surface sensor which 
can reliably facilitate prediction of severe impacts within a few 
milliseconds of the initial contact. 
Yet another object of the present invention is to provide a vehicle impact 
detection system which can reliably predict and differentiate severe 
vehicle side impacts from minor side impacts, and which is arranged so as 
to reduce the cost and complexity of servicing. 
In accordance with the present invention, a system for controlling 
actuation of a vehicle occupant safety restraint device in response to an 
impact with an outer surface of the vehicle comprises a first sensor means 
affixed to the outer surface of the vehicle for generating a continuous 
first output signal representative of a condition of the outer surface, a 
second sensor means affixed to an inner surface of the vehicle for 
producing a second output signal if the outer surface has been deformed to 
be in contact with the second sensor means, and a processor means for 
monitoring the first output signal. The processor means comprises means 
for performing signal analysis on the continuous first output signal to 
determine whether the first output signal is indicative of an impact of 
sufficient severity to require actuation of the safety restraint device, 
and prediction means responsive to the signal analysis means to generate a 
third output signal at a calculated time t. The occupant safety restraint 
device is actuated in response to the second and third output signal being 
coexistent, i.e., generated at substantially the same time. 
In further accordance with the present invention the first sensor means 
comprises a vibratory sensor, the second sensor comprises a binary crush 
sensor affixed to an inner, internal surface of a vehicle door, and the 
outer surface comprises an outer side surface of the vehicle. 
The present invention will be more fully understood upon reading the 
following detailed description of the preferred embodiment in conjunction 
with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
As shown in FIGS. 1 and 2, the vehicle impact detection system 10 of the 
present invention comprises a dual, independent sensor arrangement 12 for 
providing a continuous first output signal 14 representative of the state 
or condition of an outer vehicle surface such as the outer door skin 16, 
fenders, or other outer side surfaces of the vehicle, and a second output 
signal 18 which is produced only when a crash severe enough to crumple the 
outer door skin 16 has occurred. A control circuit 20 utilizes a processor 
22 to perform signal processing on the continuous output signal 14. As 
described hereinbelow, the processor 22 is programmed to provide an 
analysis of the sensed surface condition to distinguish deployment 
situations from nondeployment situations by evaluating vehicle outer 
surface contact to predict crash severity. 
The dual, independent sensor arrangement 12 of the present invention is 
formed by two independently operating sensor elements 24 and 26. The first 
sensor element 24 comprises a vibratory transducer connected to suitable 
processing circuitry, such as an amplifier and bandpass filter. For 
example, the vibratory transducer sensor 24 produces a continuously 
oscillating output to generate the first output signal 14. The frequency 
of the vibratory sensor output is dependent on the condition of the 
vehicle outer skin 16, and that different identifiable frequencies are 
produced in response to the different forces experienced by the outer skin 
during specific types of vehicle crash and/or impact situations. 
The second sensor element 26 comprises a binary type crush sensor switch 
which produces the second output signal 18 whenever the crush sensor 
experiences a force great enough to close an integrated switch mechanism. 
In the present invention, the crush sensor 26 produces the output signal 
18 whenever a crash has occurred which is severe enough to crush the outer 
skin 16 a predetermined distance d. The distance d is used to roughly 
discriminate between deployment and nondeployment situations. In other 
words, a vehicle crash which is severe enough to warrant deployment of an 
air bag will crush the outer skin a distance of at least d. 
In operation, the processor 22 monitors and analyzes the first output 
signal 14 to predict the type and severity of a side impact based on the 
detected frequency characteristics of signal 14. For example, the 
processor 22 could match the frequency characteristics to data 
representative of different degrees of crash type and severity located in 
look-up tables stored in a memory (not shown). If the predicted impact is 
of the type that suggests the potential need for deployment of the 
passenger safety restraint, the processor can then predict the time at 
which the crush sensor 26 should generate the output signal 18. If the 
crush sensor 26 generates the output signal 18 at the predicted time, a 
fire signal is generated to actuate deployment of the passenger safety 
restraint device. 
This operation is symbolically illustrated in FIG. 2 by processor 22 
setting a flag 28 high to produce a "1" at an input to an AND gate 30 at a 
calculated/predicted time t. If the output signal 18 appears as a "1" at 
the other AND gate 30 input at time t, then the fire signal is generated 
at the AND gate 30 output. By continuously correlating and tracking the 
vibratory sensor output 14, and matching the results against the crush 
sensor output 18, processor 22 can reliably predict deployment situations 
within a few milliseconds of the initial impact with the outer surface. 
Because system 10 can reliably predict deployment situations within a few 
milliseconds, and subsequently instantly verify the prediction with the 
crush sensor output 18, the present invention is particularly suited for 
use in controlling the actuation of an air bag in response to side 
impacts. However, one of ordinary skill in the art will readily appreciate 
that the usefulness of the present invention to predict severe surface 
impacts within a very restricted period of time is not limited solely to 
vehicle side impacts. 
Therefore, the dual, independent sensor arrangement 12 of the present 
invention advantageously utilizes the vehicle's own body structure to 
allow a single point outer sensor to effectively discriminate 
nondeployment situations, such as side impacts caused by a shopping cart, 
bicycle, etc., from severe impacts requiring deployment of the safety 
restraint without having to employ sophisticated and timely signal 
processing, or carefully tailor crush sensor thresholds, or rely on the 
ability of a processor to isolate the output of a pressure transducer. 
Further, since there is only a single point outer sensor 24, the cost and 
complexity of servicing the present invention is greatly reduced over a 
multiple sensor array system. However, since the condition of the outer 
surface of the vehicle is still being used to predict the type and 
severity of impact, a fast and reliable time-to-fire is maintained to 
permit deployment of the passenger safety restraint as early as possible. 
It will be 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, none of which departs from the 
spirit and scope of the present invention as defined in the appended 
claims.