Abstract:
A method for checking a sensor signal suitable for actuating a passenger protection arrangement of a vehicle. The method includes a step of carrying out a comparison between the sensor signal and at least one reference signal, repeatedly within a predetermined time interval, in order to obtain a plurality of comparison results, and a step of evaluating the sensor signal based on the plurality of comparison results, in order to detect a fault in the sensor signal.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method for checking a sensor signal that is suitable for actuating a passenger protection arrangement of a vehicle, a method for actuating a passenger protection arrangement of a vehicle, a corresponding device as well as a corresponding computer program product. 
       BACKGROUND INFORMATION 
       [0002]    German document DE 43 02 399 C2 discusses a method for checking an electronic device, which includes at least two acceleration-sensitive sensor systems. In this instance, output signals of the two sensor systems are integrated within a time window if the output signals exceed a minimum acceleration value. 
       SUMMARY OF THE INVENTION 
       [0003]    With this as background, the present invention introduces a method for checking a sensor signal that is suitable for actuating a passenger protection arrangement of a vehicle, a method for actuating a passenger protection arrangement of a vehicle, furthermore a device which uses at least one of these methods and finally a corresponding computer program product according to the main claims. Advantageous refinements are derived from the respective dependent claims and the following description. 
         [0004]    The present invention is based on the realization that current methods for checking the plausibility of a sensor signal do not detect certain faults of a sensor. The detection reliability is able to be improved by comparing a sensor signal not only once with a reference signal or in each case once with a plurality of reference signals but, within a time cycle, a plurality of times with one or more reference signals. In this way, a faulty sensor signal may reliably be detected. 
         [0005]    The present invention creates a method for detecting a suitable sensor signal for actuating a passenger protection arrangement of a vehicle, which includes the following steps:
       Carrying out a comparison between the sensor signal and at least one reference signal several times within a predetermined time interval, so as to obtain a plurality of comparison results; and   Evaluating the sensor signal based on the plurality of comparison results, in order to detect a fault in the sensor signal.       
 
         [0008]    The passenger protection arrangement may be an air bag, which is able to be activated in the case of a collision of the vehicle, in order to protect a passenger of the vehicle from injuries. Sensors may be situated in the vehicle so that they are able to detect collisions. The sensors may, for instance, be acceleration sensors, acoustic sensors or distance sensors. The sensor signal and the reference signal may be provided by different sensors situated in the vehicle. The sensor signal may be continually analyzed, in order to detect a collision of the vehicle For this purpose, the sensor signal may be compared to one or more threshold values. If a corresponding analysis of the sensor signal reveals that a collision of the vehicle is present or is directly ahead, provided the sensor signal has been evaluated as fault-free, the passenger protection arrangement may be actuated based on the sensor signal, that is, activated for example. The reference signal may also be suitable for detecting the collision. In the case of the fault-free functioning of a sensor providing the sensor signal and in the case of the sensor providing the reference signal, the sensor signal and the reference signal may have the same or a similar curve. 
         [0009]    For example, the sensor signal and the reference signal may be offset in time with respect to each other or may have a different signal strength. Before the comparison, the sensor signal and the reference signal may be normalized and, in addition or alternatively, be delayed in time for their agreement in time. By the comparison of the sensor signal to the reference signal, a deviation may be determined between a value of the sensor signal and a value of the reference signal. 
         [0010]    If the deviation is within a predetermined range, such a comparison result may give the information that the sensor signal is fault-free, at least with respect to the time of the comparison. If the deviation is outside the predetermined range, such a comparison result may give the information that the sensor signal is faulty, at least with respect to the time of the comparison. By carrying out the majority of comparisons within the predetermined time interval, a majority of pointers come about as to whether the sensor signal is fault-free or faulty, and with that, whether the sensor providing the sensor signal is fault-free or faulty. 
         [0011]    According to one exemplary embodiment, the comparison may be carried out cyclically within the predetermined time interval in the step of carrying out. Cyclically may mean that between two successive comparisons there are equal time spans in each case. Because of the cyclical carrying out, comparison results are continually generated which are able to be evaluated. 
         [0012]    The comparison may alternatingly be carried out using a first reference signal and at least one second reference signal. If the sensor signal is compared to a plurality of reference signals, such as three reference signals, the sensor signal may be compared first to the first reference signal, then to the second reference signal, then to a further reference signal and subsequently, starting over again, again to the first reference signal. In this context, a time interval between comparisons to the first and the second reference signal may be the same as, or different from a time interval between comparisons to the second and the further reference signal. 
         [0013]    According to one specific embodiment, the method may include a step of checking as to whether a value of the sensor signal lies within a predetermined value range. The step of carrying out may be performed if the value of the sensor signal lies within the predetermined value range. For instance, the value of the sensor signal may lie within the predetermined value range if the sensor signal exceeds a predetermined threshold value. This may be about a starting threshold for an algorithm for actuating the passenger protection arrangement. In this way it is not necessary to carry out continually the steps for checking the sensor signals. Instead, the sensor signal is only checked if an event is detected, for example, or predicted, on the basis of which the triggering of the passenger protection arrangement appears to be required. 
         [0014]    According to one specific embodiment, the sensor signal is able to be evaluated as being faulty if a predetermined number of the plurality of comparison results indicate a minimum deviation between the one sensor signal and the at least one reference signal. In this way, the evaluation of the sensor signal depends not only on one decision, but is ensured via a plurality of decisions. A sensor signal may be evaluated as being fault-free, for example, if the majority or a certain proportion of the comparison results point out that the sensor signal is fault-free. The other way round, the sensor signal may be evaluated as being faulty if the majority or a certain proportion of the comparison results point out that the sensor signal is faulty. 
         [0015]    In this instance, the sensor signal and the at least one reference signal may represent signals of sensors that are situated at different positions in the vehicle. The minimum deviation is able to be a function of the positions of the sensors. A value of the minimum deviation may be fixedly specified. Alternatively, a collision may be classified with respect to a collision type or collision severity, and as a function of the classification, a suitable minimum deviation may be selected. If the sensor signal is compared to different reference signals, for each of the reference signals its own minimum deviation is able to be defined 
         [0016]    Also, sensor signals and the at least one reference signal may represent signals of sensors which are situated in the vehicle, and the minimum deviation being a function of measuring tolerances of the sensors. In this way, it may be avoided that the evaluation of the sensor signals leads to a false result based on measuring tolerances. The lower the measuring tolerances, the lower the minimum deviation may be selected. 
         [0017]    The present invention further creates a method for actuating a passenger protection arrangement of a vehicle, which has the following steps:
       Receiving a sensor signal via an interface to a sensor;   Receiving at least one reference signal via an interface to at least one reference sensor;   Checking the sensor signal using a method according to one specific embodiment of the present invention; and   Actuating the passenger protection arrangement based on the sensor signal if no fault is detected when the sensor signal is checked.       
 
         [0022]    Consequently, the approach according to the present invention may advantageously be used in connection with known algorithms for actuating passenger protection arrangement. 
         [0023]    The present invention further creates a device that is developed to carry out or implement the steps of the method according to the present invention in corresponding pieces of equipment. This embodiment variant of the present invention in the form of a device may also be used quickly and efficiently to achieve the object on which the present invention is based. 
         [0024]    In the case at hand, by a device one may understand an electrical device which processes sensor signals and outputs control signals as a function thereof. The device may be configured as a control unit. The device may have an interface developed as hardware and/or software. In a hardware implementation, the interfaces may be part of a so-called system ASIC, for instance, which contains various functionalities of the device. However, it is also possible for the interfaces to represent discrete, integrated switching circuits on their own or to be at least partially made up of discrete components. In a software design, the interfaces may be software modules which are present on a microcontroller in addition to other software modules, for example. 
         [0025]    Advantageous is also a computer program product having program code that may be stored on a machine-readable carrier such as a semiconductor memory, a hard-disk memory or an optical memory, which is used to implement the method according to one of the specific embodiments described above when the program is executed on a device that corresponds to a computer. 
         [0026]    In the following text, the present invention will be explained in greater detail with reference to the attached drawings and by way of example. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  shows a block diagram of an exemplary embodiment of the present invention. 
           [0028]      FIG. 2  shows a flow chart of an exemplary embodiment of the present invention. 
           [0029]      FIG. 3  shows signal curves according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    In the subsequent description of exemplary embodiments of the present invention, the same or similar reference numerals are used for the elements that are shown in the various figures and act similarly; a repeated description of these elements has been dispensed with. 
         [0031]      FIG. 1  shows a schematic representation of a vehicle  100  having a device according to an exemplary embodiment of the present invention. In vehicle  100 , a sensor  102 , two reference sensors  104 ,  106  and a device  108 , for actuating passenger protection arrangement  110 , are situated. Sensor  102  is configured to provide a signal to the device  108 . Corresponding to this, reference sensors  104 ,  106  are developed for each to provide a reference sensor signal to device  108 . To do this, sensors  102 ,  104 ,  106  are connected to device  108  via suitable interfaces. Sensors  102 ,  104 ,  106  are each developed to detect a collision of vehicle  100  with an object. Sensors  102 ,  104 ,  106  may also be developed to recognize another state of the vehicle that is dangerous for the passengers, such as a rollover. Device  108  is developed in order, based on at least one of the signals of sensors  102 ,  104 ,  106 , to detect the collision or an equivalent other dangerous state of the vehicle, and responding to this, to activate the passenger protection arrangement. Passenger protection arrangement  110  may be an air bag of vehicle  100 , for example. Corresponding to this, device  108  may be an air bag control unit. 
         [0032]    According to this exemplary embodiment, device  108  is developed in order, based on the signal of sensor  102 , to detect a collision of vehicle  100 . Responding to the detection of the collision, device  108  is developed to check a signal curve of the signal of sensor  102  or individual values of the signal of sensor  102  for their correctness. To do this, device  108  is configured to compare the signal of sensor  102  to the signals of reference sensors  104 ,  106 . Corresponding comparisons are carried out within a predetermined time span after the detection of the collision. In this context, the signal of sensor  102  is compared continually and several times to the signals of reference sensors  104 ,  106 . The comparisons may be carried out according to a predetermined sequence pattern, for example cyclically. Device  108  is developed so as to activate passenger protection arrangement  110  only if the comparisons reveal that the signal of sensor  102  is plausible. Furthermore, device  108  is developed so as not to activate passenger protection arrangement  110  if the comparisons reveal that the signal of sensor  102  is not plausible. 
         [0033]    Sensors  102 ,  104 ,  106  are able to be situated at different positions in vehicle  100 . Sensors  102 ,  104 ,  106  are able to be based on the same, or on different sensor principles. Sensors  102 ,  104 ,  106  are shown in exemplary fashion. Additional reference sensors may also be used, whose signals are received by device  108  and are used to check the sensor signal of sensor  102 . According to one exemplary embodiment, for the certain triggering of air bag control units  110  in a vehicle  100 , the triggering of an air bag control unit  110  is always tied to a main sensor  102 , which generates the determining signal, and is additionally tied to a plausibility sensor  104 ,  106 , which has to be enabled. In general, the function of a sensor  102  in the system is ensured by comparing the amplitude of the output values to fixedly set thresholds. For this, for example, upon switching on, an offset regulation in a corridor about the null position may be carried out, or the signal amplitude may be held longer than one second at the measuring range stop. 
         [0034]    For the reliable detection of faults of sensor  102 , a fault detection is carried out by a plausibility check. For the fault detection, the plausibility check of the measured value of a sensor, let us say sensor  104  or sensor  106 , for example, is broadened to include the measured value of two or more sensors, such as sensors  104 ,  106 , and optionally additional sensors not shown in  FIG. 1 . According to this exemplary embodiment, the signals output by sensor  102  are compared cyclically to the signals of redundancy sensors  104 ,  106  that are present in the system. 
         [0035]    In particular, an output value of sensor  102  is compared to a redundancy sensor  104 ,  106 , that is located in the system, if sensor  102 , or rather the signal output by sensor  102 , reaches a certain value. Such a certain value, for instance, may be an algorithm starting threshold. If this comparison, within a specified time cycle, repeatedly reveals large deviations, sensor  102  is graded as faulty, so as to initiate appropriate measures in the system. The appropriate measures may include, for instance, switching off sensor  102  or components for actuating air bag  110 . The admissible deviations come about according to this exemplary embodiment from the placing of sensors  102 ,  104 ,  106  in vehicle  100  and their measuring tolerances. 
         [0036]      FIG. 2  shows a flow chart of a method for actuating a passenger protection arrangement of a vehicle according to one exemplary embodiment of the present invention. The method is able to be carried out by device  108  shown in  FIG. 1 , for example. 
         [0037]    In a step  210 , a sensor signal is received via an interface. This may be about the sensor signal of sensor  102  shown in  FIG. 1 . In a step  212 , additional reference sensor signals are received via one or more additional interfaces. This may be about the reference sensor signals of sensors  104 ,  106  shown in  FIG. 1 . 
         [0038]    In a step  214 , the sensor signal received may be checked based on the reference sensor signals. Step  214  may be carried out continually or in response to the detection of a collision. The detection of a collision may take place based on the sensor signal received or based on further data. For example, the detection may take place based on a comparison of the sensor signal to a specified threshold. In step  214 , the sensor signal received may continually be compared within a predetermined time span to the reference sensor signals. The predetermined time span may be started at the point in time of the detection of the collision. During the predetermined time span, steps  210 ,  212  may be carried out continually, so that current values of the sensor signals and the reference sensor signals are continually available. Each comparison is able to supply a comparison result. 
         [0039]    The comparison results may be continually evaluated or may be stored and evaluated after expiration of the predetermined time span, for example. The sensor signal received is evaluated based on an evaluation of the comparison results. The valuation may reveal that the sensor signal received is plausible, and is consequently suitable for actuating the passenger protection arrangement. The valuation may also reveal that the sensor signal received is not plausible, and is consequently not suitable for actuating the passenger protection arrangement. If the valuation reveals that the sensor signal received is plausible, and if the collision is graded so that the triggering of the passenger protection arrangement is meaningful, then the passenger protection arrangement are actuated in a step  216 , that is, triggered, for example. 
         [0040]      FIG. 3  shows a sequence of a valuation of a sensor signal  302 , according to an exemplary embodiment of the present invention. Besides sensor signal  302 , a first reference signal  304  and a second reference signal  306  are shown. Signals  302 ,  304 ,  306  are plotted in a graph, time t being plotted on the abscissa and amplitude A of signals  302 ,  304 ,  306  being plotted on the ordinate. The curves of signals  302 ,  304 ,  306  are shown in exemplary fashion and purely schematically. Signals  302 ,  304 ,  306  are able to be generated by sensors  102 ,  104 ,  106  shown in  FIG. 1 , for example. At a time t1, sensor signal  302  crosses triggering threshold  320 . A time window is started at the crossing of triggering threshold  320 , which extends from time t1 to time t6. During the time window, sensor signal  302  is compared cyclically to reference signals  304 ,  306 . 
         [0041]    According to this exemplary embodiment, sensor signal  302  is compared at time t2 to first reference sensor signal  304 , at time t3 to second reference sensor signal  306 , at time t4 again to first reference sensor signal  304  and at time t5 again to second reference sensor signal  306 . The distances between times t1, t2, t3, t4, t5 may be equal. From the comparisons to times t2, t3, t4, t5 there is revealed in each case a distance between a value of sensor signal  302  and a value of reference signal  304 ,  306 , to which sensor signal  302  was compared at the respective time t2, t3, t4, t5. If a distance, that comes about from a comparison, is less than a specified minimum distance, sensor signal  302  is assumed to be fault-free with respect to time t2, t3, t4, t5, at which the comparison was carried out. If the distance, that comes about from the comparison, is greater than the specified minimum distance, sensor signal  302  is assumed to be faulty with respect to time t2, t3, t4, t5, at which the comparison was carried out. From the distances revealed by the comparisons to times t2, t3, t4, t5 and the comparison results revealed from this, it is determined whether sensor signal  302  is plausible. If sensor signal  302  is valued as being plausible, actuation of a passenger protection arrangement is able to take place, based on sensor signal  302 , at time t6, for instance, that is, after the expiration of the time window. 
         [0042]    The exemplary embodiments described and shown in the figures have been selected merely as examples. Different exemplary embodiments are combinable with one another, either completely or with regard to individual features. An exemplary embodiment may also be supplemented by features from another exemplary embodiment. Furthermore, method steps according to the present invention may be carried out repeatedly and also performed in a sequence other than the one described.