Abstract:
The invention proposes a method of, and an arrangement for, detecting a pedestrian impact, wherein at least three acceleration sensors ( 10, 12, 13 ) are provided, these each being fitted on the inside of the bumper cladding ( 15 ) and each generating a signal. The pedestrian impact is detected in dependence on a time delay between at least two of the three signals. The location of impact is established with reference to the at least one time delay.

Description:
BACKGROUND INFORMATION 
       [0001]    The use of acceleration sensors to detect a pedestrian impact is described in German Patent Application No. DE 10348386. 
       SUMMARY OF THE INVENTION 
       [0002]    The apparatus and method according to the present invention for detecting a pedestrian impact have, in contrast thereto, the advantage that a configuration of at least three acceleration sensors, which are mounted on the inner side of the bumper cladding, is used. Preferably, an acceleration sensor is disposed respectively to the right and to the left, and the third acceleration sensor is disposed in the middle. By evaluating a time offset of the signals occurring from the three acceleration sensors, it is advantageously possible to detect the pedestrian impact itself, and also the impact location, in simple fashion. An evaluation circuit that is disposed in a control unit, for example in an airbag control unit, is used to evaluate these acceleration signals; some of the evaluation can also be carried out in the acceleration sensors themselves. 
         [0003]    The method and apparatus according to the present invention are characterized by their robustness. In addition, impacting objects of more than negligible width, for example a shopping cart, can be recognized if the threshold of all three sensors is exceeded practically simultaneously or within a very small, possibly velocity-dependent time interval. 
         [0004]    With the present invention, it is possible reliably to distinguish triggering from non-triggering cases. 
         [0005]    An underlying idea of the present invention is to ascertain the impact location using the at least three sensors. This is based on the fact that the propagation speed of deformation sound and solid-borne sound in the plastic of the bumper cladding is relatively slow. As a result, an acceleration sensor that is located farther away from the impact location will generate the signal later than will a sensor that is mounted in the vicinity of the impact location. 
         [0006]    Because of the proximity of at least one of the acceleration sensors to the impact location, penetration of the impacting object into the vehicle can also be recorded. An average distance of 20-30 cm from the acceleration sensor to the impact location has proven particularly advantageous. 
         [0007]    It is particularly advantageous that the respective signals of the acceleration sensors can be generated when the signal exceeds noise thresholds that are predefined or are determined adaptively, for example as a function of speed. Such noise thresholds are, for example, between 3 and 5 G. 
         [0008]    Alternatively, however, it is possible for the signals also to be generated when the signal exhibits certain signal features, i.e. shapes. This can be determined, for example, as a function of a maximum or minimum or other conspicuous signal shapes, or a specific magnitude, such as the first or second integral quotient or the differential quotient of the acceleration signal. 
         [0009]    It is additionally advantageous that a counter is provided which ascertains the at least one time offset. This counter can be a timer module that is disposed in the control unit, or it is implemented as software in a microcontroller in the control unit. The microcontroller is then the evaluation circuit. 
         [0010]    Advantageously, the time offset is determined from the first two signals that occur, i.e. the two acceleration sensors that are located closest to the impact location; and the third acceleration sensor is used, with its signal, for plausibilization. The apparatus and method according to the present invention thereby become particularly robust. 
         [0011]    It is additionally advantageous that the signals are weighted after their occurrence. This takes into account the fact that the sensor that generates the signal first, i.e. is closest to the impact location, generates the signal that is most important for analyzing the impact and the impacting object. As a result, the analysis is decisively improved and weaker signals do not have such a great effect on the analysis. 
         [0012]    Advantageously, however, the signals can also be summed or integrated over time. “Integration” here means a kind of integration that is possible in terms of calculation technology. On the basis of the first integral or its first sum, a mass determination or estimate of the impacting object can be carried out via the pulse set. This modifies the second integral or a doubly summed sum, and this second sum or the second integral can then advantageously be used to determine the penetration depth of the impacting object into the vehicle. By way of the penetration depth, it is possible to achieve good discrimination of objects that are otherwise difficult to distinguish, e.g. soft and heavy ones (such as a human being) from hard and light ones. The reason is that at a given speed, a heavy object penetrates farther into the bumper than a light one. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  shows an assemblage in accordance with the apparatus according to the present invention. 
           [0014]      FIG. 2  is a first block diagram. 
           [0015]      FIG. 3  is an acceleration/time diagram. 
           [0016]      FIG. 4  is a second block diagram. 
           [0017]      FIG. 5  is a flow chart. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Acceleration sensors for detecting a pedestrian impact have already been proposed. The problem arises here of robustly separating triggering from non-triggering cases. What is necessary here in particular is impact offset detection, since the bumper&#39;s rigidity changes along the transverse direction of the vehicle, and the sensor signals from one and the same impacting object at the same speed depends on the offset. This problem is solved by the apparatus and method according to the present invention by using at least three acceleration sensors that are disposed on the bumper cladding. In this context, the time offset of the signals of the acceleration sensors is evaluated. 
         [0019]      FIG. 1  depicts the disposition of the apparatus according to the present invention. An assemblage of three acceleration sensors  10 ,  12 , and  13  is provided on bumper cladding  15 , which is fabricated largely from plastic. The acceleration sensors are, for example, bolted to bumper cladding  15  via holders. A flexural member  14  of the vehicle is provided behind acceleration sensors  10 ,  12 , and  13 . The dashed lines indicate the propagation of signals. A distance L is provided between the sensors. 
         [0020]    If an impact then occurs at location A, sensor  10  is the first to supply a signal, at time t 0 . Sensor  12  then supplies a signal with a time offset Δt 12   1 =L/c, where L is the distance to sensor  10  and C is the propagation speed of solid-borne sound in the bumper. Sensor  13  supplies a signal having a time offset t 13   2 =2(L/c). 
         [0021]    If an impact occurs at impact location B, sensor  10  once again supplies the first signal and therefore the starting point t 0 . Sensor  12  supplies its signal with a time offset Δt 12   1 =(d/c)&lt;(L/c). Sensor  13  supplies the time offset Δt 13   2 =[(d+L)/c]&lt;2(L/c). Distance d is the distance from sensor  12  to impact point P. 
         [0022]    In the case of an impact at impact point C, sensor  12  now supplies the first signal and therefore the starting time t 0 . Sensor  10  supplies its signal with a time offset Δt 12   1 =[(L/d)/c], the distance from impact point C to sensor  10  being L−d. Sensor  3  in turn supplies a time offset Δt 13   2 =[(d+L)/c]. 
         [0023]    It is assumed in this context that the horizontal extension of the impacting object is negligible. These cases, and the calculation of the ratio of Δt 12   1  to Δt 13   2 , can be used in determining the offset, i.e. distance d. 
         [0024]      FIG. 2  explains, in a block diagram, how the signals and the counter coact. In block  20 , in the event of, for example, an impact at location A, acceleration sensor  10  generates its signal. This starts timer  21 . The time measures the time offset Δt 12   1  until sensor  12  generates its signal in block  22 . The timer will then also, in block  23 , continue to measure time offset Δt 13   2  until, in block  24 , acceleration sensor  13  also generates its signal. 
         [0025]      FIG. 3  visualizes this in an acceleration/time diagram. Here curve  3 . 1  represents the acceleration signal of sensor  10  in the context of an impact at impact point A. At time t 0 , signal  31  exceeds noise threshold  30 . The timer is therefore started at time t 0 . It measures the time offset Δt 1  until the signal of sensor  12 , here labeled with the reference character  32 , also exceeds noise threshold  30 . The timer continues, however, to count the time offset Δt 2  until signal  33  of sensor  13  also exceeds noise threshold  30 . Instead of the noise threshold, other signal features can also be used to measure the times. 
         [0026]      FIG. 4  shows the apparatus according to the present invention in a further block diagram. Acceleration sensors  10 ,  12 , and  13  are connected via two-wire conductors to a control unit ECU. Acceleration sensors  10 ,  12 , and  13  transfer their data as digital signals, for example using Manchester coding, to control unit ECU. It is possible for acceleration sensors  10 ,  12 , and  13  already to encompass a pre-processing function in their modules. Acceleration sensors  10 ,  12 , and  13  can already check the noise threshold themselves, or the check is handled by control unit ECU via microcontroller μC. For simplicity&#39;s sake, interface modules and other modules such as a triggering circuit controller are not depicted here in control unit ECU, since they are not essential to an understanding of the invention. Microcontroller μC evaluates the signals of acceleration sensors  10 ,  12 , and  13  in accordance with the invention, and applies control to pedestrian protection means FGS as a function thereof. Microcontroller μC utilizes a timer module  40  to ascertain the time offset. Alternatively, it is possible for the timer to be simulated by microcontroller μC using software technology. 
         [0027]    The method according to the present invention, which is executed in the apparatus according to the present invention as shown in  FIG. 4 , will be further explained with reference to  FIG. 5  and specifically to the flow chart depicted. In method step  500 , the sensor located closest to the collision point generates its signal. “Signal generation” here means that the signal is above the predetermined threshold, in this case the noise threshold. The counter is then started in method step  501 . This is implemented, in the example, by timer module  40 , which is started by microcontroller μC. As a consequence of the impact, sensors  12  and  13  also generate the second and third signal, respectively. The time offset is determined by counter  40 . Based on the time offset, it is possible to identify the impact location and the impact itself. This is carried out in method step  503 . In method step  504 , as an option (which is not necessarily the case), a determination is made here of the first integral of the acceleration signal in order additionally to estimate therefrom, via the pulse set, the mass of the impacting object; this is performed in method step  504 . The first signal to occur is preferably used as the signal. As a further option, the second integral is calculated here in method step  505  in order to determine the penetration depth of the impacting object. It is then possible on that basis to perform a characterization of the impacting object. Instead of the integrals that are obtained here via microcontroller μC, it is also possible to use other summation techniques. It is understood that the integration is meant to be one that a computer can carry out.