Device for triggering a passive safety system

A device for triggering a passive safety system in a vehicle upon detection of an impact. At least two acceleration sensors, the sensitivity axes of which are aligned for detecting an angle of a frontal impact, are each assigned to a signal channel which, in series with the respective impact sensor, comprises an evaluation circuit, particularly an integrator circuit for its output signals, and a threshold value circuit. During the formation of the speed integral, the physical signal course and the course of the signal edges is evaluated by several logic units in a logical unit (LOG) in order to obtain factors which influence the integration constant of integrators (by multiplication and reduction) to enlarge the area that can be evaluated.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to a device for triggering a passive safety system 
which is installed in a vehicle and is triggered by an impact. The device 
has at least two acceleration sensors, the sensitivity axes of which are 
aligned for detecting the angle of a frontal impact. Each sensor is 
coupled in series with a signal channel, which comprises an evaluation 
circuit, particularly an integrator circuit for its output signals and a 
threshold value circuit. 
German Patent 38 16 587 discloses a device of this type, which evaluates 
the signals of two acceleration sensors with cos .phi.- characteristics, 
mounted at an angle of +.phi. and -.phi. symmetrically with respect to the 
driving direction in the vehicle in its frontal area. The evaluation is 
performed such that collisions are detected which have a specific angle 
(angle .phi.) to the driving direction. 
It is an object of the present invention to provide a reliable triggering 
device in a passive safety system which has a high adaptability to any 
vehicle type, particularly an expandable triggering logic which permits 
detection and evaluation of more characteristics than previously possible. 
The principal advantages of the invention are that both the physical 
orientation of the signal relative to at least two aligned acceleration 
sensors, and the temporal development of the impact are included in the 
evaluation of a frontal impact, including an impact obliquely from the 
front within a given angle range. Thus, the triggering reliability of the 
detector according to the invention at a desired point in time is 
increased as well as the reliability in identifying only those very 
special types of impacts, for which triggering of the passive protection 
system is appropriate. 
The invention also has the advantage that certain additional physical 
phenomena are taken into account in the evaluation of the triggering 
logic, which can thus identify and distinguish other disturbance factors, 
such as: 
vehicle chassis structure (weak, flexible); 
breaking struts and columns in the vehicle; 
crumbling sheet metal of the vehicle body; 
knocking of the linkage on the vehicle; 
components that are intentionally or unintentionally movable in the case of 
an impact, such as bumpers, steering columns, engine block, etc. 
Cases that are particularly critical among those mentioned, as additional 
acceleration causes, may lead to a faulty triggering of a safety system 
and thus to injuries of occupants. 
The present invention also incorporate the improvements in the Applicant's 
German Patents 37 33 837 filed on the same date as the German Patent 
Document DE-PS 38 16 587, describing the spherical-symmetrical 
characteristics of at least two (preferably four) acceleration sensors 
oriented symmetrically to the longitudinal axis of the vehicle and in a 
plane, and the German Patent 38 16 588, filed on the same date, which 
discloses a triggering device with variable thresholds and a control 
device for the lowering and raising of this threshold; the principles 
disclosed in these patent documents are also in the evaluation logic of 
the present invention. The resulting important advantage is that the 
impact history, or time sequence, of the collision can be taken into 
account in that individual factors are linked with one another; as a 
result the integration constants can be changed. 
Another particular advantage of this arrangement is that, by means of these 
individual (correction) factors, the sensitivity of the sensors can be 
utilized almost completely (100%) over a wider angle range-here toward 
180.degree.. In other words, the triggering logic according to the 
invention can be utilized not only in a frontal impact direction, 
precisely against the driving direction, in a lateral impact, precisely 
90.degree. with respect to the driving direction; and at an angle of + or 
-45.degree. to the driving direction, but also at all intermediate angles. 
By adjustment of several thresholds (-i.sub.2), it is thus possible to 
evaluate and recognize reliably, in the oblique impact area between 
45.degree. and 90.degree. relative to the driving direction, the crash 
history by way of the physical signal course, with the angle recognition 
in the triggering logic. 
Crash signal evaluation in the triggering logic according to the invention 
is divided into several subparts which combine to influence the physcial 
signal evaluation. The process includes an assessment of the "crash 
history" as well as of the momentary crash sequence. The instantaneous 
triggering time, which is a function of the forward-shifting of the 
driver's and front passenger's head, is determined by means of speed 
integrals and path integrals, as well as thresholds and reset conditions, 
so that a reliable triggering signal is emitted by the circuit. 
The several mutually independent subparts into which the crash signal 
assessment is divided are as follows: 
considering the impact angle; 
considering the channel with respect to the threshold (single channel); 
considering the channel with respect to the threshold and a positive g-edge 
(single channel); 
considering the channel with respect to the threshold and a positive g-edge 
(dual channel); 
considering the channel with respect to a positive and negative g-edge 
(single channel); 
recognition of preceding-sign change (single channel); and 
recognition of reduced acceleration signal. 
The crash direction is determined in a variable sliding time interval t, 
which becomes active when a crash is detected at an angle between 
-45.degree. and +45.degree. is measured, and remains active until either 
an angle outside the measuring range is determined or a period equal to 
2.times.t has transpired. 
The calculated values are each set back after a fulfilling of the criteria. 
Only the angle determined from the relationship of the g-signals (that is, 
acceleration measurements expressed in gravitational equivalents; 1 g=9.8 
meters/sec.sup.2) between the two sensors ml (left) and mO (right) is 
determined and used for the evaluation. Angle determination is performed 
clockwise starting from ml (right-hand system). 
##EQU1## 
For the angle &gt;45.degree., the reciprocal value of the relationship from 
(1) is determined. 
##EQU2## 
This results in a value range of: 
EQU 0.degree. to 45.degree.: tan .alpha.=0-1 (1) 
EQU 45.degree. to 90.degree.:1/ tan .alpha.=1-0 (2) 
This result is used for calculation of the integration variables. 
During the calculation, the braking deceleration is taken into account in 
order to suppress an early change of the integration variables. 
The result of considering the angle with its evaluation is to increase the 
sensor sensitivity to approximately 100% in the case of frontal impacts 
which, because of the sensor arrangement, would therefore be recognized 
only with approximately 70% of the signal amplitude. 
Other objects, advantages and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
In order to be able to maintain the 100% sensitivity of the sensor 
arrangement according to the invention, the following integration factors 
("IF") are introduced: 
______________________________________ 
IF 1 integration factor of the angle 
determination 
IF 2 integration factor of the positive edge 
evaluation with the coupling of two channels 
(threshold) 
IF 3 integration factor of the counter of the 
exceeding of the threshold 
IF 4.0/if 4.1 
integration factor of the positive edge 
evaluation with decoupling of both 
channels (threshold) 
Reduce 1 reduction of the integration factors by 
zero crossing 
Reduce 2 reduction of the integration factors by 
signal decay 
integ 0, integ 1 
integration factors which finally affect 
the V-integration of the individual 
channels (m0, m1). 
______________________________________ 
These factors are reflected in the drawings. FIG. 1 shows two sensors, mO 
and ml, to which channels 0 and 1 are assigned on the right and left sides 
respectively. The acceleration sensors are followed in series by 
amplifiers OA and filters FL as well as threshold value elements SW. The 
signals from channel 0 and channel 1 are logically combined and evaluated 
in the logic circuit LOG, which has two outputs 0 and 1 connected 
respectively with band pass filters BF and threshold value elements for 
the threshold value a2. The outputs of the respective band pass filters 
and the associated threshold value elements for a2 are fed to respective 
integrators S1 and their associated filters F1, correcting elements K1, 
signal comparators for i1 and i2 as well as the OR-circuit for possible 
triggering at the end, as shown in FIG. 1 on the right. 
FIG. 2 shows the details of the evaluation logic LOG from FIG. 1. On the 
left, the signals mO and ml come from the sensors, and the outputs LOG 0 
and 1 are shown on the right. Reference number 3 in FIG. 2 designates an 
angle evaluation in the system of coordinates according to FIG. 5 with an 
additional time evaluation; reference number 4 is an acceleration 
evaluation minus a given deceleration time, while reference number 5 
indicates a counter which detects the number of decelerations which has 
occurred. Logic units 3 to 5 of the logic circuit are used to obtain the 
integration factors IF 1 to IF 3 respectively which are then multiplied in 
a multiplier 6. A control element 7 can also add an additional value in a 
summation point 8. The logical derivation of the integration factors IF 
4.0 and IF 4.1 for the positive edge evaluation with the decoupling of 
both channels (thresholds) takes place in logical unit 9. In logic units 
10, 11 and 12, duplication factors are obtained for the physical signal 
evaluation. In this case, the logical unit 10 takes the acceleration g 
into account over a given time. 
In logical unit 11, for obtaining the reduction factor Reduce 1, the zero 
crossing of the acceleration signals is weighted in relation to a specific 
time period, and in logical unit 12, a signal reduction takes place 
between the time t and t+1 by signal decay. 
The reduction of the individual factors takes place in the differential 
element 13 which, in turn, is connected with an integration elements 14 
and 15. In addition, a reset 16 is shown in FIG. 2 on the right, which is 
connected with outputs of logical units 10 and 11 for the resetting of the 
counter 5 and of the angle evaluation element 3. 
Based on the above, FIGS. 3 and 4 are clear, and a person skilled in the 
art knows their significance from the drawing. The same applies to FIG. 5. 
Method of Operation: 
Considering a channel (single channel): 
The evaluation determines whether one or both acceleration values mO or ml, 
within an undefined time, exceed a positive threshold with a certain 
frequency. If this is the case, the integration variable is multiplied by 
the factor IF 3. 
Considering a channel (single-channel correlation): 
This evaluation becomes operative when the acceleration value of a channel 
exceeds an adjustable threshold, and has at least a certain predetermined 
edge steepness. When these conditions are met, the integration variable is 
multiplied by the factors IF 4.0, IF 4.1. In this case, no time evaluation 
is taken into account. 
Considering a channel (dual channel): 
This evaluation becomes operative when both acceleration values mO, ml 
exceed an adjustable threshold, and also have at least a certain 
predetermined edge steepness. When these conditions are met, the 
integration variable is multiplied by the factor IF 2. In this case, no 
time evaluation is taken into account. 
Edge evaluation (single channel): 
This evaluation processes the acceleration values mO and ml individually 
and is used to reset the integration variables and the counters. When the 
acceleration value mO or ml has a positive or negative slope which is 
smaller than the comparative value, the integration is stopped 
(integration factor=0). At the same time, the counter for the channel 
consideration (single channel) as well as the starting point for the time 
window .DELTA.t of the angle consideration is reset. 
Recognition of preceding sign change (single channel): 
This evaluation becomes operative when over an adjustable range a preceding 
sign change occurs between two successive acceleration values, in which 
case the integration variables for the respective channel are reduced 
(Reduce 1). 
Recognition of reduced acceleration signal (single channel): 
This evaluation becomes operative when a sensed acceleration value is lower 
than the preceding value, by an adjustable factor. When such a reduction 
exists, the integration variables for the respective channel are reduced 
(Reduce 2). 
Physical signal evaluation: 
The physical evaluation consists essentially of the integration of speed 
(v) and path (s). For the further assessment of a crash, the integrals, 
after the adding of a fixed threshold, are compared with one another and 
evaluated. 
Speed integral: 
The v-integral integrates all g-values, the edges of which have a certain 
predetermined steepness in the positive as well as in the negative 
direction. The result of the integration is increased or decreased in 
value by the integration factor determined when considering the signal. 
The integral is reset when the input signals fall within a defined 
acceleration range a.sub.s. Within this range, the integration factor has 
an accelerating effect on the resetting. The speed integral has no maximal 
or minimal limit values which cause a further resetting. 
Path integral: 
The s-integral adds up all v-values which are offered during the sequence. 
The integral is reduced continuously. When the v-integral is given, a 
resetting therefore automatically takes place at any time. When the 
maximum or minimum value is reached, the integral is further reduced; when 
there is again a falling below a lower limit value, this further reduction 
is decreased again. The same protection as in the case of the physical 
signal evaluation applies to the speed integral as well as to the path 
integral. 
Triggering signal: 
The speed integral is compared with the sum which is composed of a constant 
and the evaluated path integral (=of the threshold shifting which is 
divided into small grids) and, when this sum is exceeded forms the 
triggering signal. This triggering signal is formed separately for both 
channels. However, a triggering actually occurs only when both of the two 
channels fall below or exceed maximum and minimum limit values. 
In the case of safety systems, such as passive restraint systems in 
vehicles, the application of the invention is particularly well suited for 
the triggering of a protection device, such as an air bag, a belt 
tightener, a rollover safety bar and other similar systems. For example, 
an air bag can be provided and triggered for the driver, another air bag 
can be provided and triggered for the front seat passenger if permitted by 
the evaluation, by means of the triggering logic according to the 
invention. In addition, belt tighteners or similar systems may also be 
activated for occupants in the front seats as well as in the rear seats. 
At the same time, lateral air bags may also be triggered, which are 
provided, for example, in the doors of a vehicle or at the roof on the 
interior side in the frontal area close to the windshield in order to 
offer an additional protection for the head and/or a rollover protection. 
In addition, safety systems and system components of the same or of a 
similar type for different parts of the body, for example, for protecting 
the knee or leg or for protecting the arms, or for similar purposes, may 
also be provided. 
A person skilled in the art may modify the above-mentioned embodiment 
without leaving the scope of the invention. In particular, such 
modifications also include combinations with the circuits and switching 
elements from the German Patents 37 33 837, 38 16 587 to 38 16 591. 
Although the invention has been described and illustrated in detail, it is 
to be clearly understood that the same is by way of illustration and 
example, and is not to be taken by way of limitation. The spirit and scope 
of the present invention are to be limited only by the terms of the 
appended claims.