Triggering process for passive safety devices in vehicles

A process for triggering a passive safety device for vehicle occupants inside a vehicle, in particular airbags, pretensioning systems, buckle switches, and roll-over bars, where--by means of electric sensors, an evaluation circuit evaluating the acceleration signals of these sensors, and triggering agents--the safety devices are triggered if the acceleration signals indicate a vehicle condition which may be potentially hazardous for the vehicle occupants. According to the invention, sensor signal characteristics will be generated from quantified sensor signals by means of an evaluation function; these sensor signal characteristics will then be differentiated and fed into an amount calculation function. The up-integrated values of these amounts will then be compared to a trigger threshold so that safety devices can be triggered, if necessary. The process according to the invention allows vehicle crash events to be fully classified whilst at the same time being easy to implement in terms of actual hardware and software requirements.

BACKGROUND OF THE INVENTION 
The invention concerns a process for triggering a passive safety device for 
vehicle occupants inside a vehicle where--by means of electric sensors 
that detect a critical vehicle condition, an evaluation circuit, and 
triggering agents for the safety device--an activation of these triggering 
agents is effected in relation to the acceleration signals supplied by the 
sensors. 
Passive safety devices for motor vehicles, such, as, e.g., airbag systems, 
pretensioning systems, or roll-over bars, serve to protect vehicle 
passengers from injuries in the event of a vehicle collision (crash) 
occurring. 
Known triggering processes of such safety devices will feed the 
acceleration signals, which are generated either by a single or even by 
two acceleration sensors, into an integration device in order to compare 
then the integration value with a crash threshold, and subsequently 
trigger the passive safety device if necessary. 
Before acceleration signals are integrated these will usually be amplified, 
filtered, and fed to an unsymmetrical limiter as known from DE 38 16 587 
A1. By means of a differential circuit a reference value will be 
subtracted from any signal generated in this way; and only then will it be 
fed into an integrator. Further processing of the integrated acceleration 
signal is effected by means of analog technology. 
In addition to the analog processing of acceleration signals, their digital 
processing is also known, for example from DE 37 17 427. There, the 
acceleration signals of two sensors will be fed into a sample and hold 
circuit after amplification and filtering; the output signals of such a 
sample and hold circuit are digitized by means of a post-connected A/D 
converter. These digitized sensor signals are then processed by a 
microprocessor. 
Such digital processing is also known from DE 30 01 780 C2 where the 
acceleration signals are converted by means of an 8 bit analog/digital 
converter and processed by an 8 bit processor. 
The cost and effort entailed by such 8 bit processing is not inconsiderable 
as it involves a very high memory storage and calculation requirement. 
Finally, from DE 41 17 811 C2, a process for evaluating sensor signals is 
known where these signals are first digitized as acceleration signals 
after analog processing. These digitized acceleration signals will be 
entered over a predefined time period in succeeding time intervals and 
stored within a shift register. The difference calculated from the current 
acceleration value and the previous acceleration value lying in the past 
by the said predefined time period will then be fed into an integrator in 
order to calculate the differential velocity whose value is used as a 
trigger criterion. However, in order to implement storage and difference 
calculation an 8 bit resolution will be required here also. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a process of the type described 
above which requires only a narrow bit width for processing the 
acceleration signals and which can therefore be implemented with low 
software and hardware requirements, and still feature a 100% certainty 
with respect to crash detection. 
According to the invention the sensor signals supplied by the acceleration 
sensors will be quantified; next, sensor signal characteristics will be 
generated by means of an evaluation function. These sensor signal 
characteristics will be differentiated and their amounts then 
up-integrated. Finally, the up-integrated values will be compared to a 
trigger threshold and the safety device triggered, if necessary. With the 
process according to this invention, the increase values of the sensor 
signals will be detected, processed, and evaluated in each time interval 
of a specified time pattern. 
The process according to this invention allows a low cost technical circuit 
implementation. In particular, following quantification, digital 
processing of the sensor signals is an option here as, for example, when 
two sensors complete with two thresholds are used for quantification, a 
maximum of 4 bits only need to be processed together. This low bit width 
is made possible by the large input quantification so that the trigger 
threshold can also be set by digital means. In addition, implementation of 
the process steps following quantification may also be effected by means 
of an existing processor or an additional mini-processor (4 bit). 
Preferably, with this process according to the invention, addition of the 
quantified sensor signals can be used as an evaluation function so that, 
for example, when two sensors complete with two thresholds respectively 
are used, there is a very simple process allowing all crash types to be 
classified at 100%. If, however, in this embodiment of the invention the 
sensitivity axes of two acceleration sensors are installed at an angle of 
+45.degree. or -45.degree. against the longitudinal axis of the vehicle in 
the direction of travel, then all direction information supplied by these 
acceleration sensors will be lost. 
In another advantageous application of the invention, this direction 
information will not be lost if--instead of using addition as an 
evaluation function--an evaluation matrix is provided such that each 
quantified sensor value can be allocated a sensor signal characteristic 
from the evaluation matrix. 
This effects an additional evaluation of the quantified sensor signals in 
relation to the direction information which will cause a significant 
comparative improvement in ignition behavior relative to the process where 
addition is used as an evaluation function. Advantageously, the matrix 
values can be selected in relation to the vehicle signature and thus be 
made consistent with the relevant vehicle by means of the crash data. 
The process according to the invention becomes particularly advantageous if 
the quantification of sensor signals is effected by means of two threshold 
values. These will be selected such that a positive or negative 
acceleration is detected; therefore, the information types "no 
acceleration", "positive acceleration"; and "negative acceleration" are 
available as quantified sensor values. 
Additionally, in some cases the use of two positive thresholds will cause 
the process according to the invention to be improved with regard to its 
trigger behavior over time. These thresholds will be defined such that the 
information types "no acceleration", "low positive acceleration", and 
"high positive acceleration" are applied. 
In a further preferred embodiment of the invention the quantified sensor 
values of two sensors will be subjected to an equivalence (identity) 
function as a further evaluation function, with equivalence (identity) 
being present if the sensor signals of the two sensors simultaneously 
indicate positive acceleration. If such an equivalence (identity) function 
supplies a positive result for sensor values that succeed each other in 
time, a linearly increasing crash signal will be generated. In addition, 
for any first-time occurrence of a positive result of this equivalence 
(identity) function an increasing crash threshold will be generated, with 
triggering being effected when the crash signal value reaches this crash 
threshold. If such an equivalence (identity) function is used the crash 
signal will be controlled such that it starts with relatively small values 
and then rises relatively sharply in line with the specified time pattern. 
This will cause an excellent time behavior, that is, it will lead to a 
very fast ignition of the safety devices in the event of a vehicle crash 
hazardous to vehicle occupants. 
If a crash threshold with an exponential course is preferably selected, 
then this has the advantage that the process according to the invention 
can cause the safety devices to be triggered at the start of a crash event 
only. 
For implementing the process according to the invention, a device according 
to claims 9 to 14 will be stated. According to these Claims, comparators 
are used for quantifying the sensor signals; the output values of these 
comparators are preferably fed to D flip flops for intermediate storage. 
Furthermore, in another advantageous embodiment two acceleration sensors 
are used such that their sensitivity axes are located at an angle of 
+45.degree. or -45.degree. against the longitudinal axis of the vehicle in 
the direction of travel. In such an embodiment a 3.times.3 matrix will be 
preferred for use as an evaluation matrix. 
Implementation of the equivalence (identity) function as an evaluation 
function is effected by means of a comparator, with a counter unit being 
post-connected to this comparator for implementing the crash signal. 
Implementation of the associated crash threshold requires a timing 
generator, a shift register operated as a counter unit, and an adding 
stage post-connected to this shift register, with the adding stage 
providing the crash threshold, the content of the shift register in the 
adding stage being added up to result in a start value, and the shift 
register being post-connected to the comparator such that it starts 
counting as soon as there is an equivalence (identity) of quantified 
sensor signals and the shift pulse is generated by the timing generator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows an airbag control unit for motor vehicles complete with 
function blocks evaluation unit 1, power unit 2, and a diagnosis computer 
3. The acceleration signals supplied by two acceleration sensors S1 and S2 
are fed into evaluation unit 1 for evaluation; based on these sensor 
signals, evaluation unit 1 will determine the vehicle state. If these 
acceleration signals indicate an impending vehicle crash, ignition 
commands will be passed via line 1a to power unit 2. If it receives 
ignition commands, this power unit will generate ignition signals for the 
trigger agents of airbags 2b, pretensioning system 2a, and buckle switch 
2c. The diagnosis computer 3 monitors and checks the functionality of the 
entire system. 
According to FIG. 3 the sensors S1 and S2 are offset against each other by 
90.degree., and, respectively, by 45.degree. against the direction of 
travel P in vehicle F, so that the sensor signals also provide information 
with regard to the direction of impact. 
A hardware implementation of evaluation unit 1 according to FIG. 1 is shown 
in FIG. 2 and comprises a quantification unit 4 and an evaluation circuit 
5. 
For quantifying the sensor signals the acceleration signal of sensor S1 
will be fed respectively into two comparators K11 and K12, and the sensor 
signals of sensor S2 into two further comparators K21 and K22. A positive 
and a negative threshold s1n, s1p or s2n, s2p are used as thresholds for 
quantification: 
sensor S1:s1p and s1n where s1p&gt;s1n, 
sensor S2: s2p and s2n where s2p&gt;s2n. 
The output of quantification unit 4 thus has 4 lines 4a that are applied to 
the input of an intermediate storage device 6 designed with D flip flops. 
On each of these lines the information types "no acceleration", "positive 
acceleration", or "negative acceleration" are available for each sensor S1 
or S2. Thus, on 4 lines, there are only 6 different types of information 
that are buffered by means of intermediate storage device 6 at constant 
time periods defined by a clock pulse signal clk. To this end, the clock 
pulse signal clk generated by a clock pulse generator 16 is fed into this 
intermediate storage device 6 via a line 16a, so that the sensor values 
are applied at its output until the next clock pulse occurs and are thus 
available at the same time, via a line 6a, at the input of a 
post-connected adding stage 7. In this adding stage 7, the quantified 
sensor signals are added up such that their sum, for each clock pulse, is 
available at the output of the adding stage 7 as a 3 bit vector, which sum 
is then fed via a line 7a to post-connected processing units. 
This addition represents an evaluation function which is applied to the 
quantified sensor signals in order to generate with each clock pulse a 
sensor signal characteristic, that is, the sum. By way of example, the 
truth table of such an evaluation function for the two sensors S1 and S2 
is to be shown below, with the sensitivity axes of these two sensors being 
arranged according to FIG. 3. Thus sensor S1--viewed in the direction of 
vehicle travel--can be designated as a left-hand sensor, and the sensor S2 
can be designated as a right-hand sensor. 
______________________________________ 
output adding 
left-hand sensor S1 
right-hand sensor S2 
stage 7 
s1p s1n s2p s2n vector V dec 
______________________________________ 
1 0 0 0 0 (0,0,0) 0 
2 1 0 0 0 (0,0,1) +1 
3 0 1 0 0 (1,0,1) -1 
4 0 0 1 0 (0,0,1) +1 
5 1 0 1 0 (0,1,0) +2 
6 0 1 1 0 (0,0,0) 0 
7 0 0 0 1 (1,0,1) -1 
8 1 0 0 1 (0,0,0) 0 
9 0 1 0 1 (1,1,0) -2 
______________________________________ 
In the columns "left-hand sensor" and "right-hand sensor" this truth table 
contains the values generated by quantification unit 4. Here, the value 
"0" indicates that the relevant threshold value was not reached, whilst 
the value "1" indicates that the relevant threshold has been reached. 
Thus, "0" signifies that there is neither a positive nor a negative 
acceleration whilst a "11" indicates a positive or negative acceleration. 
In the column "output adding stage 7", located next to the above-described 
columns, the results of the addition are entered as a 3 bit vector V. 
Finally, the last column is provided for the relevant decimal value. 
As can be seen from this truth table, the evaluation function is defined 
such that the direction information contained in the sensor signals is 
essentially lost. Thus the sensor signals received in the event of a 
vehicle crash involving a front left or front right impact are evaluated 
as (+1) (see lines 2 and 4) whilst for a corresponding crash involving a 
left rear or a right rear impact the evaluation is (-1) (see lines 3 and 
7). 
According to lines 5 and 9, a crash in the direction of travel or against 
the direction of travel will be evaluated by (+2 or -2). 
In all other cases--that is, when the specified thresholds are not 
reached,--a 0 vector is output by adding stage 7 in the event of a vehicle 
crash involving an impact from right or left (compare line 6 or line 8). 
These vectors V output by adding stage 7 will be fed via the line 7a into a 
comparator 8, a register 9, and a function unit 10 which calculates the 
difference and its amount from the vector V currently fed in and a vector 
V.sub.0 generated during the preceding clock pulse. This vector V.sub.0 is 
stored in register 9 and will be fed to function unit 10, via a line 9a, 
in accordance with the clock pulse. 
The operation carried out in function unit 10 corresponds to a 
differentiation followed by subsequent addition of the sum of quantified 
sensor values; thus the amount of the increase of successive sum values is 
applied at line 10a which leads to an integrator 13. 
In this integrator 13, the increase values calculated in successive clock 
pulses will be added up and then form a crash signal P which is compared 
to a trigger threshold K2 in a post-connected comparator 14. If this 
trigger threshold K2 is reached by crash signal P, the safety devices will 
be triggered. 
As only positive values are fed to integrator 13, the integrator content 
would always continue to increase monotonously; this would cause 
undesirable results to appear. Therefore, this integrator 13 must be reset 
at specified points in time; this is effected by means of the 
above-mentioned comparator 8, a counter 11, and a further comparator 12. 
Initially, this integrator 13 is to be reset whenever there is no trigger 
event within a predefined time period. To this end, the counter value 
generated by counter 11 will be compared, by means of comparator 12, with 
a time constant T.sub.R provided by a register RAM 15. If the counter 
value fed to comparator 12 via a line 11a exceeds this time constant 
T.sub.R, a reset impulse will be fed to integrator 13 via a line 12a. 
The reset input of counter 11 is connected with the output of comparator 8 
which comparator, via a line 8a, feeds its output signals also to an AND 
gate 25 that simultaneously receives clock pulse signal clk. The clock 
pulse signal clk will thus be released for the integrator 13 only if there 
is an output signal provided by comparator 8. 
An output signal will be generated by comparator 8 if a vector generated by 
the adding stage 7 exceeds a counting threshold K1. This counting 
threshold K1 is provided--via a line 10a--by the register RAM 15. 
By way of example, the truth table of such a comparator 8 is to be shown 
below. 
______________________________________ 
output 
vector V 
comparator 8 
______________________________________ 
(0,0,0) 
0 
(0,0,1) 
1 
(0,1,0) 
1 
(1,0,1) 
0 
(1,1,0) 
0 
______________________________________ 
This shows that comparator 8 generates an output signal only for the 
vectors (0, 0, 1) and (0, 1, 0); that is, only if a crash involving a 
front left or front right impact or a frontal impact in the direction of 
travel is to be expected. In such a case counter 11 will be reset to "0" 
and also causes integrator 13 to be reset if the crash signal P generated 
by integrator 13 does not reach the trigger threshold K2 within the time 
constant T.sub.R. This trigger threshold K2 is also stored in register RAM 
15. 
In all other cases of crash events no output signal is generated so that 
the increase values determined by these vectors V are not up-integrated 
within integrator 13 as the clock signal clk does not reach the integrator 
13. 
The two constants K1 and T.sub.R must have been made consistent with each 
other and will be determined by means of the crash data existing for each 
vehicle type. Here, these constants must be selected such that a trigger 
event is forced to occur whenever this is required, i.e., erroneous 
trigger events must not occur. The process implemented by the circuit 
layout according to FIG. 2 meets these conditions using appropriately 
selected constants K1 and T.sub.R, and in this way classifies all crash 
events fully (100%), with ignition delay times remaining within acceptable 
limits. As the point in time at which the safety devices are triggered 
must occur within a specified time period following detection of a 
dangerous crash situation by the sensors, the ignition delay time 
indicates that time interval which exceeds the aforesaid specified time 
period. 
Instead of a hardware implementation of the process according to the 
invention, the evaluation of the sensor signals can also be carried out by 
means of a simple 4 bit processor. Evaluation unit 1 according to FIG. 4 
thus comprises a quantification unit 4 and a microprocessor .mu.P. The 
other function units correspond to those shown in FIG. 1. 
A software implementation provided for such a microprocessor .mu.P is shown 
by the program flow chart according to FIG. 5. Following the start of the 
program, the program variables P, V.sub.0, and T are initialized in step 
1. Here, P represents the value of the up-integrated values of the 
increase amounts, V.sub.0 is the vector from a preceding clock pulse, 
belonging to a vector V, and T indicates the clock pulse. 
If it is known in step 2 that the airbag is operational, the sum of the 
quantified sensor signals sensL and sensR is calculated as vector V. 
Subsequently, in step 4, this vector V is compared with counting threshold 
K1 whose signification has already been described in connection with FIG. 
2. If vector V exceeds this constant K1, then the absolute amount of the 
difference between this vector V and the vector V.sub.0 that was 
calculated during the preceding clock pulse will be calculated and 
up-integrated according to the formula stated, that is, it will be added 
to the preceding integrator value P. At the same time, clock pulse T will 
also be set to "0". In any other case, this step 5 will be skipped, and 
immediately followed by step 6 where the clock pulse will be compared with 
time constant T.sub.R whose signification has also been described already 
in connection with FIG. 2. If the clock pulse T reaches this threshold, 
integrator value P will then be reset in step 7. In any other case, step 7 
will be skipped. 
If the clock pulse has not reached this time constant T.sub.R, the 
integrator value P will be compared with a trigger threshold K2 in step 8; 
and, if necessary, the safety devices within the vehicle will be triggered 
(compare step 9). If trigger threshold K2 has not yet been reached, clock 
pulse T will be set to T+1, and the current vector V will become vector 
V.sub.0 (compare step 10) before restarting again at step 3. 
The process according to the invention described by means of FIGS. 2 and 5 
is very simple and reliable with regard to the classification behavior. An 
improvement of the behavior over time will be achieved by means of such an 
evaluation of the quantified sensor signals that is based on the 
evaluation of the direction information when using two sensors S1 and S2 
arranged within a vehicle according to FIG. 2. FIG. 6 illustrates a 
hardware implementation of such an evaluation, with only a section of the 
circuit layout according to FIG. 2 being shown. Instead of the adding 
stage 7 known from FIG. 2, a parameter matrix is connected in this FIG. 6 
as a RAM matrix 71 between the intermediate storage device 6 and function 
unit 10 whose functions have already been described in connection with 
FIG. 2. FIGS. 7a and 7b, respectively, show an associated evaluation 
matrix. 
According to the embodiment shown in FIG. 7a, the quantified sensor values 
of sensors S1 and S2 are each allocated a parameter gi (i=0 . . . 8). 
Here, the quantified sensor values 0, 1, and -1 represent the information 
"no acceleration", "positive acceleration", or "negative acceleration". 
Thus the gi values are applied as 3 bit vectors V at the output of RAM 
matrix 71; these 3 bit vectors V will then be processed in a fashion 
corresponding to that used for the vectors V according to FIG. 2. It has 
been found here that an accuracy of 3 bit for a gi value is sufficient; 
each individual value can thus lie between -3 and 3. The optimum layout of 
RAM matrix 71 depends on the respective vehicle signature and must be made 
consistent with the relevant vehicle by means of crash data. 
A further improvement of the behavior in time of the process according to 
the invention is achieved by means of the evaluation matrix according to 
FIG. 7b, where quantification of the sensor signals is not effected by 
means of a positive and negative threshold Sn and Sp, but where both 
switching thresholds are positive and quantification is effected using a 
high and a low threshold, that is, where high or low acceleration becomes 
detectable. 
A software implementation is possible even when using such an evaluation 
matrix as an evaluation function and essentially corresponds to the 
program flow chart according to FIG. 5, the difference being that the 
vector is not calculated by adding the quantified sensor values but can be 
taken from the evaluation matrix. 
In addition to the process according to the invention which was described 
by means of the embodiments according to FIGS. 2 and 6, or FIG. 5, it is 
possible to effect an additional evaluation of the quantified sensor 
signals; this will improve ignition time behavior to such an extent that 
ignition time delays are essentially prevented. 
This additional evaluation can be implemented by means of hardware 
according to the circuit layout shown in FIG. 8, or by means of software 
according to the program flow chart shown in FIG. 9. 
FIG. 8 provides only a partial illustration of the circuit layout according 
to FIG. 2, with the function unit used for implementing the evaluation 
function being either designed as an adding stage 7 or an evaluation 
matrix 71. In this additional evaluation, a trigger threshold Z that can 
be shifted dynamically in an upward direction will be generated; this 
trigger threshold Z increases exponentially in line with the specified 
time pattern. As the threshold is low at the start, this means that this 
process can trigger only at the start of a crash event. In this way, the 
safety devices will be triggered directly as soon as a serious crash 
occurs. 
The quantified sensor values placed in intermediate storage will initially 
be fed to a comparator 17, via a line 6a; this comparator 17 is used to 
check whether the sensor values--as present and quantified in each time 
pulse--of sensors S1 and S2 are positive (that is, whether they indicate 
an impact direction against the direction of vehicle travel). If this is 
the case, a start impulse is fed via a line 17a into a counter 18 as well 
as into a function unit 21 that can be operated either as a shift register 
or as a counter. At the same time such a signal is applied to a NAND gate 
19 which, on receiving an appropriate input signal, generates a reset 
signal for counter 18 via a line 19a. 
With regard to this counter 18, such a start signal has the effect that its 
counter state is increased by "1". In the other case, that is, if both 
sensor values are not positive, the counter will be reset to "0". In this 
way, this counter 18 counts those sensor value pairs which successively 
indicate an acceleration in a positive direction, that is, which fall into 
the first quadrant. 
The counter state Z of this counter 18 now serves as a crash signal and is 
fed via a line 18a into a further comparator 23 which effects a comparison 
with the dynamic trigger threshold (R+K3). If this trigger threshold 
(R+K3) is exceeded by the crash signal Z, the trigger agents of the safety 
devices will be activated. 
This shiftable trigger threshold (R+K3) is generated within an adding stage 
22 by adding a count value R coming via a line 21a from function unit 21 
and increasing in line with the clock pulse to a start value K3 entered 
via a line 15c of a RAM register 15. 
In order to allow the trigger threshold to increase exponentially the count 
value R generated by function unit 21 must increase exponentially in line 
with the clock pulse. This is implemented in combination with a divider 
stage 20 which, via a line 15d, receives a divider factor n from RAM 
register 15 as well as, simultaneously, the clock pulse signal clk. This 
generates a clock pulse signal clk1 with a lower comparative clock 
frequency than clock pulse signal clk. By means of divider factor n the 
increase of the exponential trigger threshold can be varied and thus 
adapted to the vehicle signature. 
Below, the task of function unit 21 is to be further described and 
explained. Initially, it is assumed that its register content is "0". A 
start impulse generated by comparator 17 now causes a "1" to be written at 
the bit-lowest point which from this point in time onwards will be shifted 
to the left at each clock pulse signal clk1 generated by means of divider 
stage 20, with a "1" being inserted at the same time. This continues until 
the highest-value bit position has been set. At this time there will be an 
automatic switchover from the "shift register" function to the "counting 
down" function. Now register content R will be counted down to "0". As 
soon as the highest value bit extinguishes during such a countdown (that 
is, as soon as the highest value bit position is "0"), an impulse 
generated by the comparator 17 will again be taken into account so that it 
is possible to switch over again to the "shift register" function. 
At first, in the "shift register" function, only small values R="1" and 
R="11" will be output during the initial time pulses whilst with 
progressing time pulse the values R will rapidly increase: R="111" and 
R="1111". 
However, counting down is effected on a bit by bit basis and thus 
considerably slower. The result is that a specified time period needs to 
expire before the process (that is, switchover to the "shift register" 
function) can be re-activated. 
The program flow chart shown in FIG. 9 represents the software 
implementation of this expanded evaluation process by means of a 
microprocessor. Following the start of the program, the counter function 
Z, divider function n, and register content R will be set to "0" in step 
1. In step 2 start value K3 is set whose meaning was described in 
connection with FIG. 8. 
If the safety devices are operational (compare step 3), it will be checked 
in a step 4 whether one of the sensor signals S1 or S2 is "0" and the 
highest-value bit position Bit.sub.H is set. If this is the case, the 
operating mode "shift register" will be activated according to step 5. In 
any other case, this step 5 will be skipped. 
If, according to step 6, both sensor signals S1 and S2 are positive, the 
counter function Z will subsequently be increased by "1". If this is not 
the case, the counter will be reset to "0", and only step 9 will be 
carried out. The divider will be increased from n to n+1 as often as is 
necessary to reach an upper limit (step 12). When this limit B is reached 
there will be a shift operation at register R and the divider n will be 
reset to zero (step 13). 
There will be a check in step 10 as to whether a register content (R&gt;0) 
exists in operating mode "counting down". If this is the case, register 
content R will be decreased by "1", otherwise this step 11 will be 
skipped. 
However, if the operating mode "shift register" exists according to step 12 
and the counter n has reached a threshold B, then the divider n will be 
reset to "0" and the register content R will be increased by "1, whilst at 
the same time another "1" value is inserted (compare step no. 13). 
Threshold B will be selected such that the value in register R changes 
exponentially over time in an adapted fashion relative to the vehicle 
type. If the highest-value bit position is set (Bit.sub.H =1), the 
operating mode "counting down" will be set according to step 15, in any 
other case step 15 will be skipped in order to proceed with the next step 
16. 
If, however, the operating mode "shift register" (compare step 12) does not 
exist or if n&lt;B, then the sum of register content R and start value K3 is 
calculated in step 16, which sum now represents the trigger threshold, and 
compared to counter state Z. If this trigger threshold is exceeded, the 
safety devices will be triggered (compare step 17); in any other case 
there will be a return to step 3. 
The diagram according to FIG. 10 shows the operating mode of this 
evaluation process. The curves S1 and S2 indicate the course of the 
acceleration signals of sensors S1 and S2 during a crash event. At the 
start of the crash event both sensor signals simultaneously have positive 
values so that crash signal Z increases linearly, whilst at the same time 
the trigger threshold (R+K3) is generated. At the point where these two 
curves Z and (R+K3) intersect, the safety devices will trigger. 
Advantageously, this additional evaluation process can be made consistent 
with the embodiments described above such that, in addition to a 100% 
crash classification, an excellent time behavior, that is a very fast 
trigger response in the event of a crash, is achieved.