Abstract:
Method for generating an activating algorithm for rollover detection for safety-related devices in automotive vehicles Here, the safety devices in question are mainly roll bars, side airbags, and seat belt tensioners.  
     A known safety system comprises a gyrometer (angular rate or gyro sensor), which measures the rotational velocity of the rolling motion, and acceleration meters, with the electronic arrangement processing the signals coming from the gyrometer and the acceleration sensors in order to control the activation of the safety device. Here, the sensor signals are evaluated by integration for a specified period of time. In order to avoid an overflow of the integration, the ratio of the transverse acceleration to the vertical acceleration is additionally calculated, and if a specified threshold value is exceeded, integration is released. The disadvantage of this safety system is above all that, in order to avoid an overflow of the integration, further means are required in addition to the angular rate sensor, namely acceleration sensors; these only meet the purpose to be able to evaluate the angular rate sensor signals, but entail high manufacturing costs for the total system.  
     According to the invention, a theoretical characteristic rollover curve, adapted to the respective vehicle, is assumed which is approximated by means of low pass filter functions to specific cutoff frequencies and trigger thresholds respectively adapted to the rollover scenarios to be detected. The sensor signals generated by the angular rate sensor sensing the rotational velocity of the rolling motion are processed and evaluated by these low pass filter functions in order to activate a safety device, if necessary.

Description:
BACKGROUND  
         [0001]    1. Field of the Invention  
           [0002]    The invention concerns a method for generating an activating algorithm processing the sensor signal of an angular rate sensor provided within the safety system of a motor vehicle, by means of which an activation decision for activating at least one safety device of the safety system is taken in relation to the sensor signal, and with the sensor signal representing a measure for the rotational velocity of the rolling motion occurring when a rollover is imminent. Furthermore this invention also concerns a safety system for motor vehicles with at least one safety device, which safety system utilizes this activating algorithm. Here, in connection with rollover events, the safety devices in question are mainly roll bars, seat-belt tensioners, and side airbags.  
           [0003]    2. Description of the Related Technology  
           [0004]    From EP 0 430 813 B1 a safety system for motor vehicles is known which features an electronic arrangement for controlling at least one safety device in the event of a motor vehicle rolling over. The safety system comprises a gyrometer (angular rate or gyro sensor), which measures the rotational velocity of the rolling motion, and acceleration meters, with the electronic arrangement processing the signals coming from the gyrometer and the acceleration sensors in order to control the activation of the safety device. Here, the sensor signals are evaluated by integration for a specified period of time. In order to avoid an overflow of the integration, the ratio of the transverse acceleration to the vertical acceleration is additionally calculated, and if a specified threshold value is exceeded, integration is released.  
           [0005]    The disadvantage of the activating algorithm used in this safety system is above all that, in order to avoid an overflow of the integration, further signals are required in addition to the signals of the angular rate sensor, namely acceleration sensor signals; these only meet the purpose to be able to evaluate the angular rate sensor signals, but entail high manufacturing costs for the total system.  
         SUMMARY OF THE INVENTION  
         [0006]    The object of the present invention is to provide a method for generating an activating algorithm processing the sensor signal of an angular rate sensor provided within the safety system of a motor vehicle, by means of which an activation decision for activating at least one safety device of the safety system is taken in relation to the sensor signal, and with the sensor signal representing a measure for the rotational velocity of the rolling motion occurring when a rollover is imminent, and which does not feature the above-mentioned disadvantages, that is, it does not require signals from further expensive acceleration sensors for evaluating the angular rate sensor signals.  
           [0007]    According to the present invention, this object is achieved according to the following steps:  
           [0008]    a) Generation of the following theoretical characteristic rollover curve:  
           α th (ω)=−(α tip /ω lim )ω+α tip ,ω≧0   (1)  
           [0009]     where ω corresponds to the initial rotational velocity of a rolling motion of the vehicle, and α th (ω) represents the inclination angle of the vehicle, the constants α tip  and ω lim  are determined in relation to the actual vehicle and state the static tip angle of the vehicle, which—if exceeded—causes the vehicle to tip over, or the rotational velocity range, at which with ω≧ω lim  a rollover of the vehicle will occur, and the range B th  which with ω-α-combinations with α≧α th (ω) (α&gt;0, ω&gt;0) represents the associated rollover risk range where a positive activation decision is expected, and  
           [0010]    b) Generation of the activation algorithm by approximating the characteristic rollover curve ( 1 ) in the first quadrant with at least two low pass filter functions (Y 1,n , n=1,2, . . . ; Y 2,n , n=1,2, . . . ) having at least one activation threshold (S 1 ,S 2 ), by the limit frequencies (f g1 ,f g1 ) of the two low pass filter functions (Y 1,n , n=1,2, . . . ; Y 2,n , n=1,2, . . . ) and the activation thresholds (S 1 ,S 2 ) being determined such that almost all ω-α-combinations of range B 1,2  with  
           α= Y   1,n (ω)&gt; S   1   , α=Y   2,n (ω)&gt; S   2  and ω≧0   (2)  
           [0011]    are contained in range B th .  
           [0012]    Due to the fact that with the method according to the invention an activating algorithm is generated which with low pass filter functions evaluates the sensor signals generated by the angular rate sensor, the disadvantages occurring when integrators are used will be removed in a surprisingly simple fashion as the measures required to avoid an overflow—in particular, the additional sensors specified in the state of the art—are now no longer required.  
           [0013]    The method according to the invention uses for the first time a theoretical rollover characteristic as a characteristic curve model for generating the activating algorithm in accordance with the invention, which is designated as equation (1) in claim  1  and whose ω-α-graph is shown in FIG. 1, with |ω| representing the rotational velocity value of the rolling motion occurring in the x direction of the vehicle if a vehicle rollover is imminent and |α| representing the inclination angle value in the y direction of the vehicle. The ω-α graph subdivides the first quadrant into two areas which on the one hand concern vehicle conditions with ω-α-combinations that are to lead to the activation of a safety device, i.e. fire scenarios, and, on the other hand, no-fire scenarios whose ω-α-combinations are not to lead to the activation of the safety device. The ω lim ,0-combination or 0,α tip -combination represents a limit condition of a vehicle with a rotational velocity ω lim  in x direction and an inclination angle of 0° or with a rotational velocity 0 and an inclination angle (static tip angle) α tip  that leads to a rollover. These parameters are vehicle specific and, therefore, need to be determined for each vehicle type.  
           [0014]    Also, in addition to the rollover characteristic curve  1 , FIG. 1 shows three rollover scenarios with the curves  2 ,  3 , and  4 . Curve  2  shows the course of a rollover starting with a high initial velocity, whilst with curve  3  the vehicle is driven onto a screwramp with subsequent rollover. With curve  4  a quasi-static rollover is shown where the vehicle reaches the static tip angle with an angular velocity of almost zero and then rolls over.  
           [0015]    The low pass filter functions can be generated as digital filters of the 1st magnitude by means of a computer where the filter algorithm consists of linear difference equations with constant coefficients, and where recursive as well as non-recursive difference equations can be used.  
           [0016]    A filter algorithm for the first and second low pass filter function Y 1,n , n=1,2, . . . and Y 2,n , n=1,2, . . . of a recursive filter of the first magnitude here takes on the following form:  
             Y   1,n   =d   1   Y   1,n−1   +c   1   X   n−1   , n= 1,2 . . . or  
             Y   2,n   =d   2   Y   2,n−1   +c   2   X   n−1   , n= 1,2 . . .  
           [0017]    with X n  representing the digitized input sequence of the rotational velocity ω, and Y 1,n  or Y 2,n  representing the corresponding output sequence, that is the inclination angle α in binary representation. The coefficients of the filter algorithm are determined in accordance with method step (b) by approximation and defining the limit frequencies and the trigger thresholds such that condition (2) is met.  
           [0018]    The cutoff frequency (=limit frequency) is defined respectively according to the initial rotational velocity, so that an initially high rotational velocity corresponding to a high initial rotation energy leads to a high cutoff frequency with an appropriately adapted trigger threshold, that is, to a trigger threshold which is also high, whilst for a low initial rotational velocity, which corresponds to a low initial rotation energy, a low cutoff frequency with an appropriately adapted trigger threshold, that is, a trigger threshold which is also low, is defined. The values of the cutoff frequency, as well as the relevant trigger threshold, depend on the respective vehicle type as well as on the fitted safety device in the vehicle (roll bar, seat-belt tensioner, side airbag) to be triggered in the event of a crash, and therefore need to be specifically adapted to each application case in order to ensure an optimum and safe trigger behavior.  
           [0019]    For the approximation of a characteristic rollover curve in accordance with equation (1), a step function ω(t) will preferably be processed as the input sequence for the low pass filter functions; and the resulting ω-α-graph is compared with the graph of the rollover characteristic, and, if necessary, an adaptation of limit frequencies and threshold values is effected.  
           [0020]    In addition, the activating algorithm is tested by means of sensor signatures obtained from earlier vehicle tests, i.e. real sensor signatures, and/or such sensor signatures simulated within the framework of a suitable simulation environment. Using these simulation results, the trigger characteristic in the ω-α-graph is evaluated, and, if necessary, an adaptation of the limit frequencies and the associated trigger thresholds is effected.  
           [0021]    Using such a method in accordance with the invention to generate an activating algorithm, the trigger behavior can be adapted individually to each vehicle type without having first to carry out costly drive tests.  
           [0022]    In a further advantageous embodiment of the method according to the invention, additional signals of further sensors are processed by the activating algorithm, hereinafter designated as extended activating algorithm, with these sensors detecting the vehicle-condition-specific parameters indicating stability, in particular vertical acceleration, lateral acceleration, and inclination angle. Using these additional data, the trigger threshold values can be adapted dynamically to the respective vehicle condition. Thus, for example, the initial value of the inclination angle of the vehicle, or its stability due to the acceleration value in z direction can be taken into account for the activation decision. This is to achieve, in relation to the detected vehicle specific parameters, an even better differentiation according to fire scenarios—i.e. vehicle conditions that lead to a safety device being activated—and no-fire-scenarios.  
           [0023]    The activating algorithm generated by the method according to the invention can be used to advantage within a safety system for motor vehicles. Here, this activating algorithm is implemented in the control unit for the safety system, which features an angular rate sensor for detecting the rotational velocity of the rolling motion of the vehicle, and at least one safety device. The activating algorithm generated according to the invention can be implemented in analog fashion, that is, with the corresponding analog filters, or by means of software using a processor in the control unit of the safety system.&lt;&lt; 
           [0024]    The limit frequencies and the trigger thresholds are defined such that the low pass filter function for the high rotation velocities features the higher cutoff frequency and a correspondingly higher trigger threshold whilst the low pass filter function for the lower rotation velocities also requires a correspondingly lower cutoff frequency as well as a lower trigger threshold. Relevant cutoff frequency values for slow or fast vehicle rollovers are stated in the claims  9  and  10 .  
           [0025]    Thus, in accordance with a particularly preferred embodiment, a first low pass filter function features a high cutoff frequency of less than 7 Hz and a correspondingly high trigger threshold value in order to detect a fast rollover with a high initial rotation energy, whilst the second low pass filter function features a cutoff frequency of less than 3 Hz with a correspondingly adapted trigger threshold value in order to detect a rollover with lower rotation energy. In the event of fast rollovers in particular, this provides for a fast activation of the safety device. Preferably, this embodiment can be provided with a third low pass filter function, by means of which slow rollovers are detected and which thus features a cutoff frequency of less than 0.5 Hz with an appropriately adapted trigger threshold value. If three low pass filter functions are used, it is possible to achieve an optimum differentiation according to rollover scenarios, and, also according to so-called no-fire scenarios, i.e. vehicle conditions that are not to lead to a safety device being activated.  
           [0026]    Furthermore, in an advantageous embodiment the signals generated by the angular rate sensor can first be fed into a high pass filter before being processed by the low pass filter functions. In advantageous fashion, this measure reduces the zero point imprecision of the angular rate sensor so that, in particular if several low pass filter functions are used, even rollover events with very low angular rates can be detected.  
           [0027]    In a further preferred embodiment of the safety system, the extended activating algorithm is implemented in its control system in order to evaluate vehicle-specific parameters in addition to the angular rate. Preferably, using an acceleration sensor, the vertical acceleration of a motor vehicle is detected and compared with at least one adaptation threshold; and, if this adaptation threshold is exceeded, or if the actual value falls below this threshold, the trigger threshold values will be increased or decreased. Thus, the signal of such an acceleration sensor is not required for the evaluation of the angular rate sensor signal—as provided for by the state of the art—but for the dynamic adaptation of the trigger thresholds as this signal provides additional information regarding the stability of the vehicle and thus carries out some kind of a plausibility check, for example with regard to a high initial rotational velocity value. That is, that for a high value of the z acceleration signal the trigger thresholds can be set higher in spite of a high initial rotational velocity, whilst a low signal indicates a low driving stability of the vehicle and thus requires that a low trigger threshold is set. In advantageous fashion, this achieves a faster activation in the event of slow rollovers, and, at the same time, in the event of extreme situations hardly ever occurring in normal driving conditions, such as e.g. in extremely steep turns, prevents such activation.  
           [0028]    Instead of such an acceleration sensor, it is also possible to use an inclination sensor. The adaptation of the trigger thresholds is effected such that, for a large inclination angle, a low trigger threshold is set, as the driving stability will then be low; however, for a lower inclination angle, a higher trigger threshold is to be provided. In addition, the inclination sensor provides the advantage that the sign of the inclination angle can be stated. This allows the thresholds to be adapted asymmetrically, that is, if the angular rate and the inclination angle have the same sign, then a lower trigger threshold value is set, whilst if the signs are different a high trigger threshold value is set.  
           [0029]    As further vehicle specific parameters, in another preferred embodiment of the safety system according to the invention, the vertical acceleration as well as the lateral acceleration can be detected, with a dynamic adaptation of the trigger threshold values being effected by means of the quotient from lateral acceleration and vertical acceleration, on the one hand, by setting a low trigger threshold if a high value of this quotient indicates an instable vehicle condition, and, on the other hand, direct and immediate activation of the safety device if the value of this quotient exceeds a predefined fixed quotient threshold. With this type of embodiment, an improved differentiation according to fire scenarios and no-fire scenarios can be achieved.  
           [0030]    In a further preferred embodiment, instead of an acceleration transducer for detecting the lateral acceleration, an inclination sensor can be used to measure the inclination angle, with the dynamic trigger threshold values being set by means of the vehicle condition characterizing the vertical acceleration and the rotational velocity. In particular, the sensor values of the inclination sensor can be used to compare the measured values with a tip angle corresponding to the static tip angle of the motor vehicle, in order to trigger directly the safety device if the static tip angle is exceeded. This ensures that if such a rollover scenario occurs, i.e. in the event of a static rollover, the safety device is always activated.  
           [0031]    Furthermore, in another advantageous embodiment, the plausibility of the inclination angle can be evaluated by means of the vehicle condition characterizing the vertical acceleration and the rotational velocity, so that, for a plausible inclination angle value, this is set as the actual current value of the inclination angle, with this value that is evaluated as being plausible being compared at the same time with a tip threshold value corresponding to the static tip angle of the motor vehicle and the safety device being activated if the tip threshold value exceeds the amount of this value. The plausibility check is advantageous therefore as it allows driving situations that represent no-fire scenarios, such as when driving through a steep turn, to be easily detected, whilst at the same time for extremely slow rollovers—so-called quasi-static rollovers—where trigger threshold values are not exceeded—activation is effected if the tip threshold value is exceeded.  
           [0032]    However, if there is no plausible inclination angle value, the change in the inclination angle which occurs during motor vehicle operation is determined by means of an integration of the rotational velocity, and then added to the start angle; the sum is then set as the current inclination angle.  
           [0033]    Finally, in dependence of the preset current inclination angle value, the trigger threshold values can be adapted to the vehicle condition characterized by this inclination angle. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0034]    Embodiments of safety systems with an activating algorithm, which is generated by the method according to the invention, are described below in detail and illustrated by the figures.  
         [0035]    The figures below show:  
         [0036]    [0036]FIG. 1: c) ω-α-graph of equation (1) as the theoretical characteristic rollover curve,  
         [0037]    [0037]FIG. 2: a block diagram of a safety system with an activating algorithm generated according to the invention, which features an angular rate sensor and three low pass filter functions for the evaluation of the sensor signals,  
         [0038]    [0038]FIG. 3: a flow chart for the software implementation of the safety system according to FIG. 1,  
         [0039]    [0039]FIG. 4: an ω-α-diagram of the activating algorithm implemented in the safety system according to FIG. 2 complete with the activation behavior of the individual activation branches,  
         [0040]    [0040]FIG. 5: a safety system according to FIG. 1 with an additional acceleration transducer in z direction or an additional inclination sensor,  
         [0041]    [0041]FIG. 6: an embodiment modified in accordance with FIG. 5,  
         [0042]    [0042]FIG. 7: a flow chart for the software implementation of the embodiment according to FIG. 5,  
         [0043]    [0043]FIG. 8: a block diagram according to FIG. 1 with two additional acceleration transducers in z and y direction,  
         [0044]    [0044]FIG. 9: a block diagram according to FIG. 1 with an additional inclination sensor in y direction and an additional acceleration transducer in z direction,  
         [0045]    [0045]FIG. 10: a block diagram of an embodiment according to FIG. 8 where with regard to the sensor values of the inclination sensor a plausibility check is carried out, and  
         [0046]    [0046]FIG. 11: a flow chart for the evaluation of the plausibility of the α value generated by an inclination sensor. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0047]    In the figures, the same function blocks or parts with the same action are indicated by the same reference marks. The circuit block diagrams are to be understood such that the function blocks shown can be implemented with analog components or, with regard to their function, also by means of software using a processor.  
         [0048]    The description of FIG. 1 was already given in the introductory description and is therefore not to be repeated here.  
         [0049]    As a first embodiment of the safety system according to the invention, FIG. 2 shows an arrangement comprising an angular rate sensor or gyrosensor  1 , which generates a signal that is proportionate to the angular velocity ω x  (angular rate) around the longitudinal axis (x axis) of a vehicle; this signal is fed to a high pass filter HP, which can be used optionally, and to the low pass filters TP 1 , TP 2 , and TP 3  of the 1st magnitude, to which the filtered signals of the high pass filter HP are passed directly for evaluation.  
         [0050]    The output signals of the low pass filters TP 1 , TP 2 , or TP 3  are respectively fed to the non-inverting inputs of the comparators K 1 , K 2 , or K 3  that compare the filtered signals with the trigger threshold values S 1 , S 2 , or S 3  applied to the inverting inputs of the comparators K 1 , K 2 , or K 3 , with these triggger threshold values being generated by the threshold value generating units SW i , i=1, 2, 3.  
         [0051]    As soon as one of the filtered signals on the comparators K 1 , K 2 , or K 3  exceeds one of the trigger threshold values S i , with i=1, 2, 3, the H signal generated by the respective comparator K i —or by several comparators—is fed via an OR gate  2  to an ignition stage  3  for triggering a safety device not shown here.  
         [0052]    The units shown in FIG. 2—with the exception of angular rate sensor  1  and ignition stage  3 —are implemented by an activating algorithm according to the invention, using a microprocessor in the control unit of the safety system, and with the activating algorithm having the corresponding low pass filter functions Y 1,n , Y 2,n , Y 3,n  n=1,2, . . . . The three low pass filters TP 1 , TP 2 , and TP 3  are known low pass filters implemented as digital filters, for example as IIR filter of the 1st magnitude, that differ from one another in relation to the various different cutoff frequency values ƒ gi , i=1, 2, 3 and trigger threshold values S i , i=1, 2, 3. The cutoff frequencies ƒ gi  and trigger thresholds S i  are determined such that the resulting characteristic trigger curve approximates the theoretical characteristic rollover curve in accordance with equation (1), whose parameters ω lim  und α tip  are defined on a vehicle-specific basis. FIG. 4 shows the characteristic trigger curve as an ω-α-graph  1  of the implemented activating algorithm as well as the activation behavior of the three individual branches in form of the ω-α-graphs  2 ,  3 , and  4 , with even the theoretical characteristic rollover curve shown in FIG. 1 having been entered as an ω-α- graph  5 .  
         [0053]    The fire-range that is, the range where a triggering of the safety device is desired, is defined by those ω-α-combinations, to which—with the resulting characteristic triggering curve  1  as a function α(ω)—the following applies: α≧α(ω). The range of those ω-α-combinations with α&lt;α(ω) represents the no-fire range, where the safety device is not to trigger.  
         [0054]    The first triggering branch with the first low pass filter TP 1  and the associated trigger threshold S 1  corresponds to the ω-α-graph  2 , with f g1 =4.5 Hz being defined as cutoff frequency and S 1 =2 (=189°/s. ?) as the trigger threshold. This branch is used for fast triggering at a high angular rate ω x , namely for values greater than 250°/s, which, however, hardly occur in typical rollover scenarios. Curve  2  also shows that the lower threshold value, up to which there will be no triggering, is relatively high—namely at an angular rate of the vehicle around its x axis of approx. 200°/s. The other two triggering branches are adapted to rollover scenarios with an angular rate of 250°/s maximum, which occur more frequently relative to the above-mentioned situations. The curve  4  of the third triggering branch which corresponds to the third low pass filter TP 3  with associated threshold value circuit SW 3 , with the lowest cutoff frequency ƒ g3  of 0.06 Hz and a triggering threshold value S 3  of 0.22 (=17°/s?), triggers in the event of slow rollovers, with even the lower limit below which there will be no triggering having a low value, namely a vehicle angular rate value of approx. 20°/s . The curve  2  covers the intermediate range and thus includes typical rollover scenarios. The associated cutoff frequency ƒ g2  is 0.5 Hz, the associated trigger threshold value S 2  is 0.9 (=57°/s?). The specified values represent values that have already been optimized and which were determined by means of simulated sensor signatures, or the use of real crash data, and finally by concrete driving and crash trials. The aim is to define these parameters such that the greatest possible sensitivity with regard to all fire scenarios is achieved, whilst at the same time ensuring that there will be no triggering in no-fire scenarios.  
         [0055]    If you consider the triggering behavior of the overall system by means of curve  1 , it can be seen that the lower limit of ω x , where there will no longer be any triggering, corresponds to the limit of the third triggering branch (in line with curve  4  from FIG. 4). In addition, for an angular rate above 450°/s the trigger angle α increases linearly. This is caused by the limited measurement range of the angular rate sensor  1 .  
         [0056]    The embodiment described in FIG. 2, for a rollover detection by means of the activating algorithm according to the invention, requires three low pass filter functions; however, in response to the actual trigger behavior requirements, it is possible to extend this activating algorithm to more than three low pass filter functions; in this case it is possible to select smaller spacings in between the cutoff frequencies.  
         [0057]    As already described above, the high pass filter shown in FIG. 2 can be used optionally—irrespective of how many low pass filter functions have been selected. The purpose of this high pass filter function is to eliminate a low frequency drift of the angular rate sensor signal, caused e.g. by temperature fluctuations, and thus to stabilize the angular rate sensor signal. If necessary, it may be possible to do without this high pass filter function, if the temperature fluctuations only cause a minor drift.  
         [0058]    The processing steps to be executed by a microprocessor in the case of a software implementation are detailed in the flow chart of FIG. 3. According to this flow chart, following start-up (step S 1 ) the angular rate sensor signals are first digitized as ω x -values (step S 2 ). Next, in step S 3 , the filter values ωFil 1   out , ωFil 2   out , and ωFil 3   out  of the filters TP 1 , TP 2 , and TP 3  are calculated and then a comparison with the trigger threshold values S 1 , S 2 , and S 3  will be carried out (step S 4 ). If one of these trigger threshold values S 1 , S 2 , or S 3  is exceeded, a safety device will be triggered in step S 5 , e.g. a seat-belt tensioner, a side airbag, or a rollover bar. If all filtered ω x -values remain below these trigger threshold values, the method recommences with step S 2 .  
         [0059]    An improvement of the trigger behavior is achieved by an embodiment according to FIG. 5, in contrast to an embodiment according to FIG. 2, using an additional acceleration sensor  4  in z direction whose signals are processed as a z -values by a low pass filter function that is shown as low pass filter TP az1  in FIG. 5. This additional information by the acceleration sensor  4  is used, on the one hand, to carry out a dynamic adaptation of the trigger threshold values S i  (i=1, 2, 3) such that triggering will be faster for fast rollovers and earlier for slow rollovers, and, on the other hand, activation is prevented in the event of extreme situations hardly ever occurring in normal driving conditions, such as e.g. in extremely steep turns. In this regard, the acceleration signal a z  supplies additional information on the stability of the vehicle. For an a z  value of at least 1 g (=gravitational acceleration), a stable vehicle condition can be assumed. In such a case, the a z  values are processed by the low pass filter function and are used to adapt the trigger threshold values S i (α) (i=1, 2, 3) to this vehicle condition by increasing the trigger threshold values. But in reverse, if the a z  value is very low a less stable driving condition of the vehicle must be assumed, with the consequence that the trigger threshold values are lowered. Therefore, the trigger threshold values S i (α) represent a function f 1 (z1Fil out ) of the filtered acceleration signal a z  which thus supplies a redundant information in addition to the information from the ω x  values with regard to the actual vehicle position.  
         [0060]    With this dynamic threshold value adaptation, extreme situations can be reliably detected even with regard to the actual vehicle position. On the one hand, such a situation is driving through a steep turn, and, on the other hand, driving along a screw ramp with subsequent rollover. The first-mentioned situation represents a no fire scenario, the last-mentioned situation is a fire scenario. Detection and correct interpretation of these situations is made more difficult by the fact that the initial behavior of the a z  measured value is identical for the two situations, namely, a fast increase to a high value a z  with a z   &gt; 1 .  Then the a z -measured value drops down to a low value with a z &lt;&lt;1 at the screw ramp, as the vehicle passes into a weightless condition or a lateral condition similar to weightlessness, whilst in another case the a z  measured value remains on a positive g value with a z &gt;1, which is almost constant whilst driving into a steep turn. The dynamic adaptation is now effected by adapting the threshold values to the a z -value, that is, for a high a z  value the threshold values will be increased, and for a decreasing a z  value the threshold values will be decreased. This ensures that, when driving through the steep turn, there will be no triggering.  
         [0061]    The safety system according to FIG. 6 shows a possible implementation of the dynamic threshold adaptation, with this safety system—in comparison with the system according to FIG. 5—featuring three low pass filters TP azi , i=1,2,3 respectively preconnected to a threshold value circuit SW i , i=1,2,3, instead of a low pass filter TP az1  preconnected to the threshold value circuits SW i , i=1,2,3. Here, a comparator K 5 , K 6  or K 7  with a respective threshold value circuit SW 5 , SW 6  or SW 7  is provided respectively in between a threshold value circuit SW i , i=1,2,3 and a low pass filter TP azi , i=1,2,3 .  
         [0062]    The algorithm to be implemented in the event of a software implementation of the safety system features—as an extended activating algorithm and in accordance with these three low pass filters TP azi , i=1,2,3 the comparators, and the threshold value circuits SW 5 , SW 6 , and SW 7 —low pass filter functions and respectively assigned threshold values S i , i=5,6,7.  
         [0063]    The cutoff frequencies of the low pass filters TP azi , i=1,2,3 as well as the threshold values S i , i=5,6,7 of the comparators K 1 , i=5,6,7 are different and determined such that in a downward sequence the first low pass filter TP az1  features the highest cutoff frequency and the third low pass filter TP az3  the lowest cutoff frequency. For the threshold values S i , i=5,6,7 of the threshold value circuit SW 5 , SW 6 , SW 7  the same holds mutatis mutandis. If the output signal of a preconnected low pass filter TP azi  i=1,2,3 is lower than one of the threshold values S i , i=5,6,7, then the trigger threshold S i (a z ) i=1,2,3 of the respective post-connected threshold value circuit SW i  i=1,2,3 is decreased by a predefined stage; if the output signal of the respective low pass filter exceeds the threshold value again, then the trigger threshold will also be increased.  
         [0064]    In order to increase the reliability of an activation in the event of a slow rollover, i.e. a so-called static rollover, it is possible to post-connect an additional low pass filter TP az,stat —shown in FIGS. 5 and 6 as an option (together with a comparator K 4  and a threshold value circuit SW 4 )—to the acceleration sensor  4  or to implement the same in the extended activating algorithm as a further low pass filter function. With the low pass filter TP az,stat , the vibrations will initially be filtered from the acceleration signal a z  and fed to a comparator K 4  at its inverting input. A threshold value circuit SW 4  generates a trigger threshold value S 4  corresponding to the static tip angle of the vehicle, which, when the actual filtered a z -value drops below the trigger threshold value S 4 , via a connection to OR gate  2  causes a safety device to be activated by ignition stage  3 . This drop below the trigger threshold value is interpreted as the transition from a stable vehicle position, where the acceleration sensor  4  indicates a value around 1 g, into an unstable vehicle position marked by a low a z  value of the acceleration sensor  4 . For the associated trigger threshold value S 4 , a correspondingly low value will therefore be selected, 0.5 g for example.  
         [0065]    For the software implementation of the extended activating algorithm generated for the safety system according to FIG. 5, FIG. 7 shows a flow chart which essentially corresponds to that from FIG. 3. The differences are only in that, additionally, in step S 2  the a z  values are also digitized, in a step S 4  the corresponding filter values z 1 Fil out  are generated, and in relation to these filter values, trigger threshold values S i (a z ), (i=1, 2, 3) are set as a function f i (z1Fil out ) . The remaining steps S 6  and S 7  correspond to those from FIG. 3.  
         [0066]    In addition to the implementation of the tip angle detection by means of the low pass filter TP az,stat , of comparator K 4  and the associated threshold value circuit SW 4 , in step S 4  the filter values z 2 Fil out  of filter TP az,stat  are calculated, in order to carry out—subsequent to step S 6 , if the trigger threshold values S i (a z ) (i=1, 2, 3) are not exceeded—a comparison of the filter values z 2 Fil out  with the trigger threshold value S 4  corresponding to the static tip angle (step S 7 ).  
         [0067]    Instead of the acceleration transducer  4  in the safety systems according to the FIGS. 5 and 6, an inclination sensor  5  can be used as shown by a connection line (drawn as a broken line) to the low pass filters TP α1 , TP α,stat  in FIG. 5, or to the low pass filters TP αi , i=5,6,7 in FIG. 6. Correspondingly, as already described above, when the α-values have been filtered by a low pass filter TP α1  or TP αi , i=5,6,7 these values are used for the dynamic adaptation of the trigger threshold values S i (α) (i=1, 2, 3). The advantage of this measure is that these α values provide additional information on the stability of the vehicle. It is assumed here that for appropriately large a values there is only a low driving stability, that is, the trigger threshold values need to be lowered, so that even for low ω x  values activation takes place. As the inclination sensor  5  also supplies the sign of the tip angle, the trigger threshold values can be adapted asymmetrically, that is, if the ω x  values of the angular rate and the α values have the same sign, then a lower trigger threshold value is set, whilst if the signs are different a high trigger threshold value is set.  
         [0068]    The dynamic adaptation of the trigger threshold values S 1  (i=1, 2, 3) can also be carried out, in accordance with FIG. 8, by means of the transverse and vertical acceleration values of the vehicle. Here, the DC capable acceleration sensor  4  in z direction and the DC capable acceleration sensor  6  in y direction are preferably used, both being respectively post-connected by a low pass filter TP az  or TP ay , implemented as filter functions in the processor of the control unit. Both acceleration values processed by the filter functions, that is the filtered a z  and a y  values are fed to the threshold value circuits SW i  (i=1, 2, 3) for the dynamic adaptation of the trigger threshold values S i (a z ,a y ) (i=1, 2, 3), that is, they are set in relation to the filter function values zFil out , and yFil out , i=1, 2, 3 . From these filtered acceleration values, it is possible to determine additionally the value and direction of acceleration, and thus the inclination angle, for the corresponding adaptation of the trigger threshold values, as already described and shown above.  
         [0069]    Furthermore, if DC capable acceleration sensors are used, it is possible to evaluate the stability of the current vehicle condition by means of the lateral acceleration/vertical acceleration ratio; this is done, for example, by decreasing the trigger threshold values S i (a z ,a y ) (i=1, 2, 3) if this ratio has a high value thus indicating an unstable vehicle condition. Furthermore, the sign of the lateral acceleration can be used to make the trigger threshold values dependent on the sign of the rotation direction of the vehicle rollover such that if the signs are equal a lower trigger threshold value is set than for different signs.  
         [0070]    Finally, a function—shown in a circuit arrangement  11 —can be used to calculate the ratio of the a y /a z -value amounts (as filter values) from lateral to vertical acceleration and used directly via a comparator K 4  and by means of a threshold value circuit SW 4  to generate a fixed trigger threshold value S 4  for the activation of a safety device. As this ratio states the inclination angle of the vehicle, the trigger threshold value S 4  can be set in line with the static tip angle α tip  of the vehicle.  
         [0071]    The flow chart for the software implementation of the safety system according to FIG. 8, corresponds essentially to the embodiments described above and is not to be shown here.  
         [0072]    The embodiment of a safety system according to FIG. 9 represents a combination of the two alternatives shown in FIG. 5, where in addition to an angular rate sensor  1  an acceleration sensor  7  in z direction and an inclination sensor  8  in y direction are provided. The dynamic adaptation of the trigger threshold values S i (α;a z ) is effected in relation to the α-values of the inclination sensor  8  and the a z -values of the acceleration sensor  7 , filtered by means of an appropriate low pass filter function, by increasing the trigger threshold values in the event of high a z -values, taking into account the direction information of the α-value, and, in a reverse case, by decreasing the trigger threshold values, that is for low a z -values.  
         [0073]    In order to implement a static trigger branch, the filtered α-values will not only be fed to the threshold value circuits SW i (i=1, 2, 3) but their values are also applied to the non-inverting input of a further comparator K 4 , with a threshold value circuit SW 4  being connected to its inverting input. This threshold value circuit SW 4  generates a trigger threshold value S 4 (ω,a z ) in relation to the applied filtered ω x -values of the filter TP 3  and the a z -values, which trigger threshold value is large for large a z -values as such a z -values indicate a stable vehicle condition. If the ω x -values also increase, then the trigger threshold value can be increased even further, so that there will not even be an activation as such a situation also indicates a stable vehicle condition, e.g. a steep turn. For low a z -values and, at the same time, high ω x -values the trigger threshold value S 4 (ω,a z ) is decreased, however.  
         [0074]    The final embodiment according to FIG. 10 differs from the embodiment described last above essentially in that, additionally, the change of the inclination angle Δα int =∫ω x dt during vehicle operation is calculated from the ω x -values by integration using an integrator circuit  12 , from which change—together with the start angle α start , representing the value at the start of the vehicle operation or the value set at the start of the activating algorithm routine—the current inclination angle α curr  is determined, which is then set in turn for the next routine as start angle α start .  
         [0075]    In relation to the start angle α start  (and the direction of inclination can also be taken into account here) there will be a dynamic adaptation of the trigger threshold values S i (α), with these angle values α start  being fed to the threshold value circuits SW i (i=1, 2, 3) by an angle measurement unit  13 .  
         [0076]    Furthermore, a plausibility unit  11  is provided which checks the α-values generated by the inclination sensor  5  for plausibility by means of the ω x -values supplied by the angular rate sensor  1  and the a z -values supplied by acceleration sensor  4 . The advantage of these measures is that, on the one hand, no-fire scenarios can be determined more easily, and, on the other hand, more precise information on the current inclination angle can be generated. Due to the plausibility check, an “incorrect” α-value of the inclination sensor can be detected so that an activation of the safety device in spite of a no-fire event can be excluded with a large degree of probability.  
         [0077]    The risk of an “incorrect” α-value being indicated is based on the physical principle of standard inclination sensors. Thus, there are sensors that indicate the level of a liquid and, for this reason, indicate correspondingly slowly, or for short and sharp acceleration events in their sensitivity direction, lead to a “spillover”, i.e. the value indicated will be too large. If an acceleration sensor in y direction is used as an inclination sensor, the problem is that, if a filter is used to smooth the sensor signals, the system consisting of sensor and filter responds too slowly in the case of fast events. The aim, therefore, needs to be the elimination of the vibrations laid over the actual useful signal.  
         [0078]    Initially, the angle measurement unit  13  will define the current inclination angle α curr , obtaining at vehicle start up, as the start angle α start . Starting from this start angle α start  the current angle α curr  is calculated by the integration of the ω x  value using the integrator unit  12  and the addition of the start angle α start  in accordance with α start +Δα int .  
         [0079]    With increasing time duration, however, the current inclination angle α curr  calculated by means of integration will deviate more and more from the actual inclination angle due to fault tolerances. Therefore, using plausibility unit  11 , a plausibility check of the sensor values will be carried out and the current actual inclination angle α curr  correspondingly determined in relation to the result of the check carried out by the angle measurement unit  13 .  
         [0080]    The conditions under which an α-value is evaluated as being plausible are to be described by means of the flow chart in accordance with FIG. 11. Initially, the ω x  value must remain underneath a specified threshold S ω  in order to exclude the “incorrect” values occurring due to the inertia of the liquid existing in an inclination sensor or the inertia of the system “acceleration sensor in y direction and filter” (step S 1 ).  
         [0081]    According to step S 2  the change speed of the ω x -value must not exceed a specified threshold S dω . If this threshold is exceeded, this means that forces act on the liquid existing in an inclination sensor that may lead to an “incorrect” α-value.  
         [0082]    According to step S 3  the a z -values filtered with a long term filter (that is, a large time constant) must only be within a value range around the value 1 g, which range is specified by an upper threshold S no  and a lower threshold S nu , for example between 0.7 g and 1.3 g. Only in this case will there be a stable vehicle condition such that the inclination sensor is also able to supply a “correct” value. The condition according to step S 4  is used to check whether the vehicle is being driven across a bumpy track. To this end, the a z  values are filtered with a short term filter (that is, a small time constant) and the amount of these filtered values compared with a threshold S m . If this threshold is exceeded, this means that there is a bumpy track such that the inclination sensor could supply “incorrect” values.  
         [0083]    In step S 5 , it is additionally checked whether the speed of change of the α-value, which is measured on a threshold S dα , is not too high, as in such a case forces act on the vehicle that cause the inclination sensor liquid to wobble; with the consequence that “incorrect” values are generated.  
         [0084]    Finally, it will be checked whether the α-value is consistent with the a z -value measured by the acceleration sensor in z direction, as the last-mentioned value must approximately correspond to cos α.  
         [0085]    If all conditions mentioned in steps S 1  to S 6  are met, then the relevant α-value will be evaluated to be plausible (step S 7 ). However, if one of these conditions is not met, then the α-value will be evaluated as being not plausible (step S 8 ).  
         [0086]    An α-value that has been evaluated as plausible will be set as the current value α curr  and as the start angle α start =α curr . When the extended activating algorithm has been run through, α start  defines the start angle “old” according to α start,old =α start . If an α-value is detected as not being plausible, then the current angle α curr  is yielded by α start,old +Δα int  and the start angle “new” as α start =α curr . Before a new routine is started, α start,old =α start  is again reset.  
         [0087]    If the α-value most recently detected as being plausible lies too far back in time, then the increased trigger threshold values S i (α), i=1,2,3 can either be reset in several stages to their basic values, or reset immediately to these basic values.  
         [0088]    In order to detect driving situations where an activation is not desired, the function branch built up with the comparators K 5 , K 6 , and K 7 , the NAND gate  10 , and the AND gate  7  is used to detect a steep turn. The comparators K 5 , K 6 , and K 7  are respectively assigned to a threshold value circuit SW i (for i=5, 6, 7) generating a threshold value S i , with the ω x -value generated by the angular rate sensor  1  being fed—for comparison with the threshold value S 5 —to the comparator K 5 , and the a z —value generated by the acceleration sensor  4  in z direction to the comparator K 6 , and the α-value generated by the inclination sensor  5  to the comparator K 7 . If the threshold values S i (i=5, 6) are exceeded by the respective measured values, whilst at the same time the actual α-value drops below the threshold value S 7 , a logical L value is applied at the output of the NAND gate  10 , which blocks the AND gate  7  such that an H signal applied at the other input of this AND gate  7  does not cause—via the OR gate  8 —the ignition agent  3  of a safety device to be activated.  
         [0089]    Activation is to be prevented in all cases where, for example, the vehicle drives through a steep turn, as otherwise the high ω x  value which occurs during such an event would cause the safety device to be activated. The threshold value S 5  is set such that the ω x -value which occurs when driving through a steep turn is exceeded. In addition, an a z -value occurs in such a driving situation which is significantly above the value of 1 g, which is why the corresponding threshold value S 6  is set to approx. 1 g. When driving through the steep turn, due to the superelevation of the road surface and the centrifugal acceleration occurring with the use of a liquid inclination sensor, however, the α-value will deviate only a little from 0°, that is, it will remain below a specific value. Therefore, the α-value will be fed to the inverting input, and the threshold value S 7  to the non-inverting input of comparator K 7 .  
         [0090]    If very slow rollovers occur where the trigger threshold values S 1 (α) (for i=1, 2, 3) are not exceeded, then—for activating the safety device—the α-value amount which occurs will be compared by means of a comparator K 4  with a trigger threshold value S 4  corresponding to the static tip angle of the vehicle and generated by a threshold value circuit SW 4 . If this trigger threshold value S 4  is exceeded, an activation will be effected only if the corresponding α-value has been evaluated as plausible by the plausibility unit  11 , so that in consequence a H signal is applied at both inputs of the AND gate  9 , thus activating the ignition stage  3 .