Abstract:
A sensor system for impact detection is situated in the front region of the vehicle. The sensor system is able to detect kinematic variables in both the longitudinal and vertical directions of the vehicle. The sensor system is suited in particular for truck underride crashes.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a sensor system for impact detection. 
   BACKGROUND INFORMATION 
   The use of external sensors in a restraint system for impact detection has been described in German Patent Publication No. 196 09 290. 
   Upfront sensors currently in use are acceleration sensors installed in the front deformation zone of the vehicle, i.e., on the radiator crossmember, which detect only in the longitudinal direction of the vehicle. It is possible for the acceleration sensors to be able to detect in the Y direction as well, for example for detecting the crash direction. The upfront sensors are basically used for improved detection of frontal problem crashes such as oblique impacts, truck underride crashes, and impacts on soft obstructions, for example, collisions with large animals such as moose, horses, or cattle. 
   In truck underride crashes, which carry a high risk of injuries and are centrally detectable much too late, and in which the upfront sensors are actually intended to enable timely deployment, it happens in currently used upfront sensors and sensor configurations, i.e., sensor systems, that the less mechanically stable radiator crossmember is bent upward or downward, depending on the height of the impact object, before the impact is detected. As used here, “impact object” refers to the rear part of a truck, i.e., the truck trailer underride protection, the truck trailer longitudinal chassis beam, the truck trailer hitch, or the bottom edge of the flatbed truck. The impact vehicle longitudinal chassis beams enter under these objects. This is why these crashes are so hazardous and are centrally detectable so late. 
   The upfront sensors which are sensitive only in the X direction are disoriented by the impact and, depending on the impact combination, are able to detect only a larger or smaller portion of the deceleration component in the X direction. Unfortunately, there have been several cases in truck underride crashes in which the occupant protection system did not deploy, or deployed too late, because of disoriented upfront sensors and the occupants were injured. 
   SUMMARY OF THE INVENTION 
   The sensor system for impact detection according to the present invention has the advantage over the related art that a sensor system for front end impact detection is provided which has a sensor system that is able to detect kinematic variables in both the longitudinal direction and the vertical, i.e., Z direction of the vehicle. This is particularly advantageous for truck underride crashes, in which such external sensors, generally referred to as upfront sensors, are intended to allow timely deployment of restraining means. In particular, it may happen that the parts of the chassis on which the upfront sensors are mounted are bent during the crash, so that the upfront sensors are no longer oriented in the longitudinal direction of the vehicle. Rather, it is expected that the upfront sensors then become oriented upward or downward approximately in the vertical direction. 
   Therefore, the present invention provides for the use of sensors which detect kinematic variables in the vertical direction of the vehicle as well, so that it is then possible to detect kinematic variables in the longitudinal direction of the vehicle even if there is bending. Upfront sensors which are sensitive only in the longitudinal direction, and thus the X direction, of the vehicle become disoriented by such an impact, and, depending on the impact combination, are able to detect only a larger or smaller portion of the X component of the deceleration. The simplest embodiment, therefore, is to provide acceleration sensors in the X and Z directions as upfront sensors. However, it is also possible to use acceleration sensors situated at an angle to the X and Z directions so that the crash direction may also be detected by, for example, multiple such obliquely situated acceleration sensors. An additional Y sensor may also be used here for detecting the crash direction as well as for plausibility checking. 
   It is particularly advantageous to provide acceleration sensors to detect the kinematic variables, and thus in this case, the acceleration in both the longitudinal and vertical directions of the vehicle. As described above, the acceleration sensors may be oriented directly in the longitudinal or the vertical direction of the vehicle, and also at an angle thereto, for example at 45°. Other sensors which are able to detect such kinematic variables in an impact may also be used here. 
   The first and second acceleration sensors are advantageously mounted in a common housing. This economizes on cable length and simplifies installation of the sensor system. Alternatively, however, the acceleration sensors may also be mounted in separate housings. This may result in simplification. 
   The sensor-system is connected to a control unit for restraint systems so that, based on the signals from the first and second acceleration sensors, the control unit is able to detect which sensor is oriented in the longitudinal or in the vertical direction of the vehicle, or at an angle thereto. The control unit detects this by virtue of which sensor sends the signal having the higher absolute value. In an impact, a longitudinal component of the vehicle sends a stronger signal than does a vertical component of the vehicle. As a result, in such an impact the sensor oriented most closely to the longitudinal direction of the vehicle sends the stronger signal, even when the radiator is bent. The sensor system may be situated on the upper crossmember of the radiator. It may be provided that pairs of such first and second acceleration sensors are situated on both the left and right side of the radiator crossmember, or that only a single pair is centrally situated on the radiator crossmember. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a block diagram of the sensor system according to an embodiment of the present invention. 
       FIG. 2  shows an alternative configuration of the acceleration sensors according to an embodiment of the present invention. 
       FIG. 3  shows a rotation of the sensors during a crash. 
       FIG. 4  shows a schematic illustration of the installation site for the upfront sensors. 
       FIG. 5  shows another schematic illustration of the installation site for the sensors. 
       FIG. 6  shows a model of the deformation zone and the installation site for the upfront sensors. 
   

   DETAILED DESCRIPTION 
   According to the present invention, a sensor system is situated in the front of the vehicle and is configured in such a way that the kinematic variables may be detected in both the longitudinal and vertical directions of the vehicle. For this reason there is an upfront sensor which is provided with acceleration sensors generally having two channels, thus, in the X and Z directions. The sensor system may also be configured in such a way that also the accelerations in the transverse direction of the vehicle and/or other kinematic variables are detectable. The crash direction may also be easily identified in this manner. 
   In a normal crash, i.e., one in which the radiator crossmember is not bent upward or downward before deployment, the acceleration sensor in the upfront sensor, and thus in the sensor system, which is sensitive in the X direction detects the problem crash. This is an example in which the strongest acceleration signal in the X direction is used in the deployment algorithm for integration. Although the sensors in the sensor system which are sensitive in the Z direction detect the Z components of the acceleration, which are present in every crash, these components are much smaller than the X components of the acceleration and have only secondary relevance for specifying the time of deployment. The sensors which are sensitive in the Z direction could be used for plausibility checking. Furthermore, the information about the Z direction may also be advantageously used for impact detection or impact discrimination. 
   If radiator crossmembers are deformed before the deployment, which may occur in severe problem crashes in which the upfront sensors which are sensitive only in the X direction have already failed multiple times, the X sensors no longer detect the X components of the acceleration, or detect these components only partially, because these sensors are now oriented more or less in the direction of the Z axis. If the radiator crossmember and thus the upfront sensors are rotated upward, the original X sensors detect in the Z direction, and the Z sensors provided according to the present invention detect in the X direction. For a downward rotation, the original X sensors detect in the Z direction, and the original Z sensors detect in the X direction. Corresponding equivalents, in which the Z sensors are oriented in the Z direction and/or the X sensors are oriented in the X direction from the outset, may be implemented as well. 
     FIG. 3  shows exemplary sequences in the case of rotation of the sensor system. System  30  is still correctly oriented, and the acceleration sensors detect in the X and Z directions. System  31  has now been rotated upward, so that the original X sensor detects in the Z direction and the original Z sensor detects in the X direction. System  32  has been rotated downward, and here the original Z sensor detects in the X direction and the original X sensor detects in the Z direction. These are ideal cases; in the normal case the sensors are situated at an angle to the coordinate system, even with a rotation, so that this must be taken into account in the evaluation. 
   A bent radiator crossmember, and thus a rotation of the sensor system, is recognized by the fact that in a crash the original Z sensors detect the signal having the higher absolute value, and the original X sensors detect the signal having the lower absolute value. It is thus recognized that an impact has occurred, which for an occupant protection system having exclusively central detection represents a problem crash. In these cases, an algorithm for forming the deployment decision may either be set to a default parameter setting, or the Z signals are used for specifying the time of deployment. 
   Consequently, a crash may be satisfactorily detected even by rotated sensor systems and actually disoriented sensors, and protection may thus be provided for the occupants. This represents a significant improvement in occupant safety. 
     FIG. 1  shows in a block diagram one example embodiment of the system according to the present invention. A sensor  10  oriented in the Z direction as an acceleration sensor is connected to a first data input of a sensor signal processor  12 . An acceleration sensor  11  oriented in the X direction is connected to a second data input of sensor data processor  12 . Sensor data processor  12  is connected via a unidirectionally or bidirectionally configured data transmission line to a control unit  13  for restraint systems. Control unit  13  is in turn connected to restraining means  14  such as airbags, seat belt tensioners, or roll bars. 
   Upfront sensors  10  and  11  for sensor data evaluation unit  12 , which also has a transmission component for transmitting the previously digitized and processed data to control unit  13 , are used for impact detection. Alternatively, it is also possible to orient sensors in the Y direction for better detection of the crash direction. Control unit  13  evaluates the signals, and as a function of these signals influences the deployment algorithm and thus the decision to deploy restraining means  14 , and also evaluates other appropriate data such as occupant detection and additional sensor data from other sensors situated, for example, in control unit  13  itself, for example for plausibility checking of the signals from sensors  10  and  11 . Sensors  10  and  11  as well as sensor data evaluation unit  12  may be mounted in a common housing. However, sensors  10  and  11  may be situated in separate housings with separate sensor data evaluation units. The data transmission here is strictly unidirectional from sensor data evaluation unit  12  to control unit  13 . This simplifies the design and thus saves on costs. Alternatively, this connection may have a bidirectional design, or may be joined to a bus connection. 
     FIG. 2  shows that sensors  10  and  11  may each be simulated by obliquely situated sensors  20  and  21 . This enables improved detection of the crash direction. If both sensors  10  and  11  were replaced by such sensors  20  and  21 , four sensors would be present. 
     FIG. 4  shows exemplary installation sites for the sensor system according to the present invention. Here the installation sites for the sensor system according to the present invention are illustrated on a radiator crossmember  41  of a vehicle  40 , in the front region of the vehicle. The sensor system is situated either centrally at location  43  or on both left and right sides at locations  42  and  44 . Regardless of where it is installed, the sensor system according to the present invention is then connected to a centrally situated control unit  45 . 
     FIG. 5  shows in an additional schematic illustration the installation site for the sensor system according to the present invention. Sensor system  51  is installed in vehicle  50  very high up on the radiator crossmember. 
     FIG. 6  shows in a schematic illustration the location of inventive sensor system  61  in a vehicle  60  in relation to the crash zone. In a vehicle, a distinction is made between a deformation zone  62 , which is deformed at low speeds, and a deformation zone  63 , which is deformed only at high speeds, between the impact object and the vehicle. Sensor system  61  according to the present invention is situated in the transition zone between the deformation zone for low speeds and the deformation zone for high speeds. This is very advantageous for the operating mode of the sensor system. A typical acceleration sensor has a measuring range of ±220 g and a sensitivity of 9 mV per g. The acceleration sensor has self-testing capabilities and is easily mounted in a plastic housing.